File organization and management com 214 pdf

Continue 1 1 UNESCO-NIGERIA TECHNICAL - VOCATIONAL EDUCATION REVITALISATION PROJECT-PHASE II NATIONAL DIPLOMA IN COMPUTER TECHNOLOGY FILE Organization AND MANAGEMENT YEAR II- SE MESTER I THEORY Version 1: December 2 2 Content Table WEEK 1 File Concepts... 6 :... 7 Binary figure... 8 Representation... 9 Transmission... 9 Storage... 9 Storage unit... 9 Abbreviation and symbol More than one bit, trit, dontcare, what? RfC on trivial Alternative Words WEEK 2 WEEK 3 Identification and File Aspects of File Systems File Names Metadata Hierarchical File Systems Means Secure Access WEEK 6 Types of File Systems Disk File Systems File Systems File Systems Transactional Systems File Systems Network File Systems Special Purpose File Systems 3 3 File Systems and Operating Systems Flat File Systems File Systems according to Unix-like Operating Systems File Systems according to Plan 9 from Bell Files under WEEK 7 File Storage Backup Files Purpose Storage Primary Storage Secondary Storage Third Storage Out Storage Features Storage Volatility Volatility UncertaintyAbility Availability Availability Performance Key Storage Technology Semiconductor Magnetic Paper Unusual Related Technology Connecting Network Connection Robotic Processing Robotic Processing File Processing Activity 4 4 Technology Execution Program interrupts secure mode and memory control mode Virtual Memory Operating Systems and UNIX Microsoft Windows Mac OS X Special File Systems Journalized File Systems Graphic User Interfaces History Mainframes Microcomputers Microsoft Windows Plan Unix and Unix-like operating systems Mac OS X Real-time Operating Systems Built-in Core Development Hobby Systems Pre-Emptification 5 5 WEEK 1 THIS WEEK SPECIFIC LEARNING OUTCOMES To understand: The concept of the file in the computing concept, field, character, and bits in relation to File 5 6 6 Concept Files In this section, we will deal with the concepts of the file and their relationship. Many operating systems view files as a set of . At a higher level where the contents of the file are viewed, these binary numbers may represent more general values or text symbols, or anything else. It's up to the program, using the file to understand the meaning and internal layout of the information in the file and present it to the user as more meaningful information (such as text, images, sounds). At any given time, the file may be in size, usually expressed by bytes, indicating how much memory is associated with the file. In most modern operating systems, the size can be any number up to the system limit. However, the total File doesn't require its its size has any real value if the data in the file does not match the data in the permanent storage pool. The information in a computer file may consist of smaller packets of information, often called records or lines, that are individually different but have some common traits. For example, a salary file may contain information about all employees of the company and their salary data; each entry in the payroll file concerns only one employee, and all records have a common trait to be associated with wages. It's very similar to placing all the salary information in a specific closet in an office that doesn't have a computer. A text file may contain lines of text corresponding to printed lines on a piece of paper. In addition, the file may contain an arbitrary binary image (BLOB) or may contain a complete one. The way information is grouped into a file depends entirely on the person projected by the file. This has led to a plethora of more or less standardized file structures for every conceivable purpose, from the simplest to the most complex. Most computer files are used by computer programs. These programs create, modify, and delete files for their own use as needed. Programmers, creating programs, decide what files are needed, how they should be used and their names. 6 7 7 In some cases, computer programs manipulate files that are visible to the computer user. For example, in a word processing program, a user manipulates files of documents that she calls herself. The contents of the document file are designed in such a way that the text processing program understands, but the user chooses the name and location of the file, and it provides the bulk of the information (such as words and text) that will be stored in the file. Many apps pack all their data files into a single file, using internal markers to recognize the different types of information inside. Files on your computer can be created, moved, modified, grown, shortened, and deleted. In most cases, computer programs that run on the computer handle these operations, but the computer user can also manipulate the files if necessary. For example, Microsoft Word files are typically created and modified by Microsoft Word in response to user commands, but users can also move, rename, or delete those files directly using a program such as Windows Explorer. In Systems Similar to Unix, userspace processes usually don't apply to files at all; The operating system provides a level of abstraction, which means that almost all interactions with files from the user space are through hard links. Solid links allow the name to be With a file (or they may be anonymous - and therefore temporary); files have no names in the OS. For example, a user's space program can't delete a file; he can link to a file (e.g. using a rm or mv shell command or, in an anonymous case, just leaving), and if the kernel determines that there are no more existing links to the file, it can delete the file. In fact, it's really just a core that deals with files, but it serves to process all interactions between the user and the space with (virtual) files in a way that is transparent to the user's space programs. Bit: The bit is simply defined as binary digits, which with 0 to 1 s. Bit is the smallest storage unit. 7 8 8 Number of bits SI prefixes Binary prefixes Title (Symbol) Standard SI Binary Use name (symbol) Value (kb) (Kibit) 2 10 (Mbit) (Mibit) 2 20 (Gbit) gibit (Gibit) 2 30 tera (Tbit) (Tibit) 2 40 (Pbit) (Pibit) 2 50 (Ebit) (Eibit) 2 60 (sbit) zebibit (Sibit) 2 70 (Ybit) yobibit (Yibit) Bit binary figure taking the value to either 0 or 1. Binary numbers are the main unit of information storage and communication in the field of digital computing and digital information theory. Information theory also often uses a natural figure called either nit or nat. The quantum computing also uses cubes, one piece of information that is likely to be true. The bit is also a unit of measurement, an information capacity of one binary digit. It has a bit symbol, or b (see discussion below). Binary figure Claude E. Shannon first used the word bit in his 1948 work Mathematical Communication Theory. He explained its origins by John W. Tooky, who wrote Bell Labs 8 9 9 9 memo on January 9, 1947, in which he contracted binary digits to just bit. Interestingly, Vannevar Bush wrote in 1936 about bits of information that could be stored on the punches used in mechanical computers of the time. A little storage can be both on and off (0). One bit is one or zero, true or false, flag that is on or off, or in general, the amount of information needed to distinguish between two mutually exclusive equally likely states from each other. Gregory Bateson defined a bit as the difference that makes the difference. Parts of representation transfers can be implemented in many forms depending on the context. For example, in digital circuits in most computing devices, as well as , a little electrical impulse generated by an internal clock in a control unit or data register. For devices that use positive logic, the logical value of 1 (true value) is up to 5 volts, while the logical 0 (false value) is represented by 0 volts. Storage bits are manipulated into the computer's volatile memory, and can be stored permanently on a continuous basis storage device, such as a tape or disk, as well as on optical discs. It is important to distinguish between the use of a bit when discrete storage unit and the use of a bit when using a statistical unit of information. A bit, like a discrete storage device, can by definition only store 0 or 1. The statistical bit is the amount of information that can be stored in a discrete bit on average. Thus, it is the amount of information that is chosen between two equally likely outcomes. One bit corresponds about nats (ln (2)), or Hartley (magazine 10 (2)). 9 10 10 Consider, for example, a computer file with a thousand 0s and 1s that can be compressed without loss into a file of five hundred 0s and 1s (on average, on all files of this kind). The original file, although it has 1,000 bits of storage, has no more than 500 bits of information entropy, as the information is not destroyed as a result without loss of compression. A file can have no more theoretical bits of information than bits of storage. If these two ideas need to be distinguished, sometimes a bit of the name is used when discussing data storage, while Shannon is used for a statistical bit. However, most of the time, the meaning is clear out of context. The abbreviation and symbol No Uniform Agreement has been reached yet on what the official symbols of the unit for the bit and roll should be. One of the commonly cited standards, IEC 60027 of the International Electrical Commission, states that the bit should be a unit symbol for a bit of a unit (e.g. kbit for kilobit). In the same standard, o and B symbols are listed for byte. Today, the agreed ISO/IEC standard :2008 abolishes and replaces subclauses 3.8 and 3.9 IEC :2005 (those related to information theory and prefixes for binary multiples). Another widely cited relevant standard, IEEE 1541, defines b to be a unit symbol for bit and B to be that for a bye. This convention is also widely used in computing, but until now has not been considered internationally acceptable for several reasons: both of these symbols are already used for other units: b for barn and B for bel; bits are already short on binary numbers, so there's little reason to cut it further; it is customary to start the one symbol from the top letter only if the device was named after a person (see also Claude Emil Jean-Baptiste Liter); 10 11 11 instead of te, the term (one symbol: o) is used in some fields and in some French- speaking countries, which adds to the difficulty of the agreement of the international symbol; b is sometimes also used for byte, along with bits for bits. The bel unit is rarely used on its own (only as a decibel, db, which can hardly be confused with decibute), so the chances of conflict with B for byte are quite small, although both devices are very often used in the same areas (e.g. telecommunications). More than one bit of A byte is a set of bits that originally differ in size from the context, but now almost almost eight bits. Eight-china bytes, also known as octets, can represent 256 values (2 8 values, 0,255). The four-to-four number is known as , and can represent 16 values (2 4 values, 0 15). A rarely used term, crumb, can refer to two bits and can represent 4 values (22 values, 0 3). The word is a term for a slightly larger group of bits, but it doesn't have a standard size. It is the size of a single register in a computer processor. In the architecture of IA-32, better known as x86-32, 16 bits are called word (with 32 bits being a double word or dword), but other architectures have words sizes of 8, 32, 64, 80 or other. Conditions for large bits can be formed using a standard range of SI prefixes, such as kilobit(kb), (Mbit) and gigabit (Gbit). Note that there is a lot of confusion about these units and their abbreviations (see above). When a little inside a group of bits such as a honeycomb or word should be transmitted is usually determined by a number from 0 (not 1) up, corresponding to its position within the side or word. However, 0 can be either the most significant bat or the least significant bat depending on the context, so the convention used should be known. 11 12 12 Some instructions on a computer processor (such as a set of bits) work at the level of manipulating bits rather than manipulating data interpreted as a set of bits. Telecommunications or transmission speeds are usually described in terms of bits per second (bit/c), not to be confused with bod. A bit of binary figure? A number is a name used in positional notation when using the base (speak) 03:56, May 30, 2008 (UTC). It is noted that the decimal form of SI factors (10-2, 10 x4..) is used in connection with telecommunications. So we can agree that 56 per second essentially means bits per second. This thus gives us bytes per second. However, when we switch to per second, shouldn't we use a binary form of prefix, i.e. bps/1024 kilobytes per second? Beats, didn't bit also 12.5 cents? how in two bits equating a quarter? Like in shaving and haircut, two bits? if so, this should be expressed in this article, and the conclusion must be explained. Many thanks! Kingturtle 23:00, 24 April 2005 (UTC) Bit, trit, dontcare, what? Two is to a little like three is three, how five to what? I called them quintessentis, but call it a layoff. Or nibble and a little. The correct name will be a hiwari figures, so the quints are probably as correct as anything. RfC on trivial bits of Nibble: Nibble 1/2 byte. Typically, it's 4 bits, for example 0110, 13 13 Byte: This is a collection of 2 or 8 bits. For example, a number of number of bits that can be considered as a computer unit. It is a symbol. It can also be described as the smallest computer memory unit. The word byte has closely related values: a contiguous sequence of fixed number of bits (binary numbers). Using byte to mean eight bits was almost ubiquitous. A contiguous sequence of bits inside a binary computer, which includes the smallest address sub-fact of the natural size of a computer word. That is, the smallest binary data unit that can use meaningful calculations, or natural data boundaries. Decimal value SI k kilo M mega G giga T tera P peta E exa zetta Y yotta- Binary Value IEC JEDEC Ki kibi- K kilo mi mebi- M mega Gibi- G giga Tebi Pi pebi ei exbi qi zebi y yobi- a byte is the main measurement unit for storage. In many computer architectures, it's a unit of memory, most often consisting of eight bits. A byte is one of the main integrated data types in some programming languages, especially in system programming languages. 13 14 14 A byte is an orderly collection of bits, with each bit denoting one binary value of 1 or 0. The size of the bet can vary and is usually determined by the main operating system of the computer or equipment, although the 8-bit byte is the standard in modern systems. Historically, te size has been determined by the number of bits needed to represent a single character from the western set of symbols. Its size was usually determined by the number of possible characters in the supported character set and was chosen as a computer word size division. Historically, bytes have ranged from five to twelve bits. The popularity of THE IBM System/360 architecture, dating back to the 1960s, and the explosion of microcomputers based on 8-bit microprocessors in the 1980s made eight bits by far the most common size for byte. The term octet is widely used as a more precise synonym where ambiguity is undesirable (e.g. in definitions of protocols). There has been considerable confusion about the value of the metric - or SI prefixes - used with the word byte, especially with regard to prefixes such as kilograms - (K or K) and mega- (M) as shown in the prefix chart for bit and bet. Since computer memory comes in force for two rather than 10, most of the software and computer industry use binary ratings for SI-prefixed quantities, while manufacturers of computer storage devices prefer SI values. This is why the hard drive of the computer advertised with 100GB of decimal storage capacity actually contains no more than 93GB of 8-bit (power 2) address memory. Because of the confusion, the contract that determines the number of bytes must determine what prefixes mean from the point of view of the contract (i.e. alternative binary equivalents or actual decimal values, or binary score, actual values). To make the meaning of the table absolutely clear: KiB consists of 1,024 bytes. The MiB consists of 1024,1024, or 1,048,576 bytes. Bytes. the numbers in the column using 1024 raised to powers 1, 2, 3, 4 and so on are in the bytes units. 14 15 15 Alternative Words After bit, byte, and nybble, there have been some analogue attempts to build unambiguous terms for bit blocks of other sizes. All this is strictly jargon, and not very often. 2 bits: crumb, quad bike, quarter, taiste, taidbit 4 bits: nibble, nibble 5 bits: nickel, nyckle 10 bits: deck 16 bits: plate, playte, chomp, chawmp (on 32-bit machine) 18 bits: chomp, chawmp (on a 36-bit machine) 32 bits: lunch, dynner, gawble (on 32-bit machine) 48 bits: gobble, gawble (under circumstances that remain obscure) Character: Character is the smallest unit of information. It includes letters, numbers and special characters such as; The questions are -, q, %, etc. field: The field is made up of symbols, or is simply defined as a combination of characters. This is an attribute that can be assigned values. For example, name, age, gender, date of birth, etc. Record: Record is a collection of organizations and related areas. File File is a collection of organized and related records. 15 16 16 File Identification and Organization is a collection of organized and related records. Files and folders are located in the hierarchy. Files are usually available with names .5000.) In some operating systems, the name is associated with the file itself. In other files, the file is anonymous and indicates links that have names. In the latter case, the user can identify the name of the link with the file, but it is a false analogue, especially where there are multiple links to the same file. Files or links to files can be located in directories. More generally, however, the directory may contain either a list of files or a list of links to files. As part of this definition, it is important that the term file includes directories. This allows for the existence of directory hierarchies, i.e. directories containing sub- direction. The name that refers to the file in the catalog should be unique. In other words, the catalog should not have the same names. However, in some operating systems, the name may include a type specification, which means that the directory may contain an identical name for more than one type of object, such as a directory and file. In the environments in which the file is named, the file name and the path to the file directory must unequivocally identify it among all other files in the computer system. No two files can have the same name and path. If the file is anonymous, the named links to it will exist in the namespace. Any character line may or may not be a well-formed name for a file or reference depending on the context of the application. Whether the name is well formed depends on the type of computer system used. Early computers allowed only a few letters or numbers in the name of But modern computers allow long names (some up to 255) containing almost any combination of unicode letters or unicode numbers, making it easier to understand the purpose of the file at first sight. Some computer systems allow file names to contain gaps; others don't. The sensitivity of file names is determined by the file system. Unix file systems are generally case-sensitive and allow user-level applications to create files whose names differ only in the case of symbols. 16 17 17 Microsoft Windows supports several file systems, each with different case sensitivity policies. The fat shared file system can have several files whose names differ only if the user uses the disk editor to edit file names in the directory records. Custom applications, however, generally do not allow the user to create multiple files with the same name, but is different in the case. Most computers organize files in the hierarchy using folders, directories, or directories. The concept is the same regardless of the terminology used. Each folder may contain an arbitrary number of files, and may also contain other folders. These other folders are called subflanders. Subflanders can contain even more files and folders and so on, so creating a tree-like structure in which one master folder (or the root of a folder name varies from one operating system to another) can contain any number of levels of other folders and files. The folders can be called the same as the files can (except for the root folder, which often has no name). Using folders makes it easier to organize files logically. When your computer allows you to use folders, each file and folder has not only its own name, but also the path that identifies the folder or folder in which the file or folder is located. A special symbol, such as slash, is used along the way to separate file and folder names. For example, in the illustration shown in this article, the way /Payroll/Managers unequivocally identifies a file called Managers in a folder called Salary, which in turn is contained in a file called Payroll. The folder and file names are shared by slashes in this example; the top or root folder has no name, so the path starts with a slash (if the root folder had a name, it would precede this first slam). Many (but not all) computer systems use extensions in file names to help determine what they contain, also known as file type. On Windows computers, extensions consist of a period point at the end of the file name, followed by several letters to determine the file type. Expansion.txt identifies text file; a.doc extend defines any type of document or documentation Microsoft Word file format And so on. Even when extensions are used in 17 18 18 computer systems, the degree to which the computer system recognizes and century them Vary; in some systems they are necessary, while in other systems they are completely ignored if they are present. Database: It is a collection of organized and related files. For example, the institution's staff, student, and file equipment collection is called the Institution's Database. This data collection is designed to be stored in computer memory and is designed for easy access by authorized users. The data can be in the form of text, numbers, or encoded graphics. Since its first pilot introduction in the 1950s, databases have become so important in industrial societies that they can be found in almost every area of information. Government, military and industrial databases are often severely restricted, and professional databases tend to have limited interest. However, a wide range of commercial, government and non-profit databases are available to the general public and can be used by anyone who owns or has access to the equipment they need. Small databases were first developed or funded by the U.S. government for agency or professional use. In the 1960s, some databases became commercially available, but their use was sent through several so-called research centres that collected information requests and processed them in batches. Online databases are databases accessible to anyone who can link them to them using a computer. For the home user, the necessary equipment includes a computer terminal, telephone and modem, which allows the terminal and database (usually some type of search engine) to carry out intercommunal communications. Modified TVs can also be equipped to produce some specially designed databases. The user simply dials the service number, provides a password code for identification and billing, and dials in matters of the selected database on the keyboard terminal. The resulting data can be displayed either on the terminal screen or printed. The purpose of implementing the database Implementation database was caused by problems of file system 18 19 19 i. Data redundant ii. No standard iii. Lack of central control iv. Lack of Data Independence Basic Structuring Concept - Type of Essence - Type of Attribute - Type of Relationship - Group related entities - Group related entities called type of essence Problem file systems environment - Lack of data integration - Lack of central control - Inconsistency - Excess - Lack of multiple representation Chart of the usual file processing system User user environment User User N Transaction 1 Transaction N Operating System 19 20 20 Conceptual Diagram of the Centralized Database User User User Appearance External View External/Conceptual View External/Conceptual Mapping conceptual view of DBMS Conceptual/Internal View Operating System The two main operations in the database are: - - (inset, deletion and modification) - Request (to extract the necessary records that satisfy this condition) Methods of data abstraction - Classification - Aggregation - Association - Generalization 20 21 21 Database Users include - Database Administrator - End users - Application Database Organization - Physical Organization (kind of storage) - Logical organization (conceptual appearance) - Manipulation structure (external appearance) character, byte and bits in relation to file Search, reading, writing, bring, paste, delete and update operations 22 23 23 FILE PROCESSING OPERATIONS Computer file is a block of arbitrary information, or a resource for storing information that is available for a computer program and is usually based on some kind of solid storage. The file is durable in the sense that it remains available for software to use after the current program is completed. Computer files can be seen as a modern analogue of paper documents that have traditionally been stored in the files of offices and libraries that are the source of the term. File processing operations involve different activities in the file. These operations are summarized, as shown below; File Creation: The process of creating a file is called creating a file. Search: Search is a search for data in a file with a link to a special field of each record/data called a key. The key is a unique file used to identify a particular record in a file. If the record needs to be inserted into the file, it must be uniquely key. Extract/reading: This includes reading existing data from a storage form or input environment. Writing: Writing is an act of recording data on some form of storage. Removal: This means removing a record or a piece of data from a storage environment, such as a disk/tape. File Update: This is the act of changing values in one or more file records without changing the file organization. This makes the file up-to-date by adding the latest data to the file. Sorting: Sorting means regrouping the data in ascending or descending order. It involves the location of grouped data elements in a predetermined sequence to facilitate file processing. 23 24 24 Calculation: Arithmetic or logical manipulation of data in a file is called calculation. Request/interrogation of files: This is the receipt of specific data from the file according to a set of search criteria. File merging: Combining multiple sets of data files or records to create just one set, usually in an orderly sequence called file merging. Reporting: A report is a file processing operation that produces (print) of a report from a file in a given format. File Display: The contents of the data file may appear on the computer screen as a soft copy or printed on paper as a printed copy. File Storage: When you create a file, it is stored in the appropriate storage environment, such as drive, flash drive, tape, drum, etc. Data processing is widely used in business, engineering and science, and increasingly in almost all areas where computers are used. Businesses use data processing for tasks such as payroll preparation, accounting, accounting, inventory control, sales analysis, and the processing of bank and credit card statements. Engineers and scientists use data processing for a wide range of applications, including seismic data processing for oil and mineral exploration, analysis of new product samples, processing of satellite imagery, and analysis of scientific experiments. Data processing is divided into two types of processing: database processing and transaction processing. The database is a set of general records that can be searched, accessed and modified, such as bank account records, school transcripts, and income tax data. In processing databases, a computerized database of 24 25 25 is used as a central source of reference data for calculations. Transaction processing refers to interactions between two computers in which one computer initiates a transaction and the other computer provides the first data or calculations needed for that function. Most modern data uses one or more databases on one or more central sites. Transaction processing is used to access and update databases when users need to immediately view or add information; other data programs are used at regular intervals to provide summary reports on the activities and status of the database. Examples of systems that include all of these features are automated ATMs, credit sales terminals and airline booking systems. THE DATA-PROCESSING CYCLE Data Cycle is a chain of processing events in most data processing applications. It consists of data recording, transmission, reporting, storage and search. The original data is recorded for the first time in a computer-readable form. This can be achieved in several ways: manually entering information in some form of computer memory using a keyboard, using a sensor to transmit data to magnetic tape or floppy disks, by filling ovals on a computer readable paper form, or by swipes of credit card through the reader. The data is then transferred to a computer that handles data processing functions. This step involve the physical movement of recorded data to a computer or transmitting it electronically over telephone lines or over the Internet. See the store and extract information. After how Reach your computer's memory, the computer processes it. Computer operations may include access to and updating of the database, as well as creating or modifying statistical information. After processing the data, the computer reports the brief results to the program operator. As the data is processed, the computer stores both changes and original data. This repository can be both in its original data entry form and in 25 26 26 carefully controlled computer forms of data, such as magnetic tape. Data is often stored in several locations for both legal and practical reasons. Computer systems can fail and lose all stored data, and the raw data may be required to recreate the database in the state it was before the crash. The final step in the data processing cycle is to find stored information later. This is usually done to access the records contained in the database, to apply new data processing features to the data, or if some of the data has been lost to recreate part of the database. Examples of data search in the data cycle are the analysis of sales revenue in stores with verifiable data identifying new models of customer spending and the use of new seismic data processing techniques to detect oil or mineral deposits that have previously been overlooked. The history of data processing is largely, data processing has been the driving force behind the creation and growth of the computer industry. In fact, it precedes electronic computers for almost 60 years. The need to collect and analyze census data became such an insurmountable task for the United States Government that in 1890, the U.S. Census Bureau contracted the American engineer and inventor Hermann Hollerit to develop a special data processing system. Using this system, the scribes recorded the data by punching holes in a dollar-sized paper card. These cards were then sent to the census office, where mechanical card readers were used to read the holes in each map, and mechanical machines were used to tabulate the results. In 1896, Hollerit founded the Tabulating Machine Company, which later merged with several other companies and eventually became the International Business Machines Corporation (IBM). During World War II, scientists developed various computers designed for specific data processing functions. The Harvard Mark I computer was built from a combination of mechanical and electrical devices and was used to perform calculations for the U.S. Navy. Another computer, built in the UK 26 27 27 Colossus, was an all-electronic computer designed to hack German Messages. This allowed the British to quickly and effectively crack German codes. The role of the electronic computer in data processing began in 1946 with the introduction of ENIAC, the first all-electronic computer. U.S. Military used ENIAC to tabulate the paths of artillery shells and missiles. In 1950, Remington Rand introduced the first non-military electronic programmable data processing computer. This computer, called UNIVAC, was originally sold by the U.S. Census Bureau in 1951; some others were eventually sold to other government agencies. With the purchase of uniVAC in 1954, General Electric Company became the first private computer company to own a computer, soon followed by Du Pont Company, Metropolitan Life and United States Steel Corporation. All of these companies used UNIVAC for commercial data processing applications. The main advantages of this machine were its programmability, its high-speed arithmetic capabilities, as well as its ability to store and process large business files on multiple magnetic tapes. In 1952, when the American Broadcasting Company (ABC) used UNIVAC during a live television broadcast to predict the outcome of the presidential election, UNIVAC attracted national attention. Based on less than 10 percent of the election declarations, the computer correctly predicted Dwight D. Eisenhower's landslide victory over his rival Adley E. Stevenson. In 1953, IBM released the first of its computers, the IBM 701, a machine designed for mass production and easily installed in a customer building. The success of the 701 led IBM to manufacture many other commercial data processing machines. Sales of the IBM 650 computer were a particularly good indicator of how quickly the business world has adopted electronic data processing. Initial sales forecasts were extremely low because the car was considered too expensive, but more than 1,800 were eventually made and sold. In the 1950s and early 1960s, data processing was essentially divided into two separate areas: business data processing and scientific data processing, with 27,28 28 different computers developed for each. In an effort to keep data processing as similar as possible to standard accounting, business computers had arithmetic schemes that did calculations on the tithing lines (numbers with numbers that range from 0 to 9). Computers used to process scientific data have sacrificed an easy-to-use decimal number system for a more efficient binary numbers system in their arithmetic scheme. The need for separate business and scientific computing systems has changed with the emergence of a family of IBM System/360 machines in these machines that could run the same data processing programs, but at different speeds. They can also perform either numbers per digit of a math favored business or binary notation favored for scientific applications. Several models had special in which they could run programs from earlier IBM computers, especially popular IBM Since that time, almost all commercial computers were of general purpose. One notable notable to the trend of general purpose computers and programming languages is a supercomputer. Supercomputers are computers designed for high-speed, high-precision scientific computing. However, supercomputers are sometimes used to process data that is not scientific. In these cases, they should be built in such a way that they are flexible enough to allow other types of computing. The division between business and scientific data processing has also influenced the development of programming languages where application programs were written. Two such languages that are still popular today are COBOL (COmmon Business Oriented Language) and Fortran (FORmula TRANslation). Both of these programming languages were developed in the late 1950s and early 1960s, with COBOL becoming the programming language of choice for business data processing and FORTRAN for scientific processing. In the 1970s, other languages were developed, such as C. These languages reflect the general character of modern computers and have allowed the development of extremely effective programs for almost any data processing application. One of the most popular languages 28 29 29 currently used in data processing applications is the extension of C. C. C. THE was developed in the 1980s and is an object-oriented language, a type of language that gives programmers more flexibility in developing complex applications than other programming language types. 29 30 30 WEEK 3 THIS WEEK SPECIFIC LEARNING OUTCOMES To understand: How well the file system is performance in terms of extraction, insertion, update and reorganization. 30 31 31 File Systems and File Managers File System provides a mapping between the logical and physical representations of the file through a set of services and an interface. Simply put, the file system hides from users all the specific aspects of file manipulation. The main services of the file system include; Maintaining a file plot (knowing the location) of B/O support, especially the transfer mechanism and from the main memory management of secondary storage Exchange i/O devices providing protective mechanisms for information held in the system As the computer organizes, names, stores and manipulates files around the world called its file system. Most computers have at least one file system. Some computers allow you to use several different file systems. For example, new MS Windows computers support older files like FAT MS-DOS and older versions of Windows, in addition to the NTFS file system, which is a regular file system for the latest versions of Windows. Each system has its advantages and disadvantages. Standard FAT allows only eight character file names (plus three extension symbols) without spaces, while NTFS allows for a lot more names that can contain gaps. You can call the pay file records in the NTFS, but in FAT you would be to something like payroll.dat (unless you've used VFAT, an EXTENSION of FAT that allows long file names). File manager programs are utility programs that allow you to manipulate files directly. They allow you to move, create, delete and rename files and folders, when in fact they do not allow you to read the contents of the 31 32 32 file or store information in it. In Windows, the most commonly used file manager program is Windows Explore.r File System In computing, the file system (often also written as a file system) is a method of storing and organizing computer files and the data they contain to make it easy to find and access them. File systems can use a storage device, such as a hard drive or CD-ROM, and include maintaining the physical location of files, they can provide access to data on the file server, acting as customers for network protocol (e.g. NFS, SMB or customers), or they can be virtual and exist only as a method of access for virtual data (e.g., procfa). A more formal file system is a special database for storage, hierarchical organization, manipulation, navigation, access and data search. Aspects of file systems Most familiar file systems use a basic storage device that offers access to an array of fixed-size blocks, sometimes called sectors, usually 2 in size (512 bytes or 1, 2, or 4 KiB are the most common). File system software is responsible for organizing these sectors into files and directories, and tracking which sectors belong to which file and which are not used. Most file systems address data in fixed-size units called clusters or blocks that contain a certain number of disk sectors (usually 1-64). This is the smallest logical amount of disk space that can be allocated to store a file. 32 33 33 However file systems do not need to use a storage device at all. The file system can be used to organize and provide access to any data, regardless of whether it is stored or dynamically generated (e.g. ). File names, whether the file system has a basic storage device or not, file systems usually have directories that link file names to files, usually by connecting a file name to an index in a file distribution table of some kind, such as FAT in the DOS file system, or inode in a file system similar to Unix. Catalogue structures can be or allow hierarchies in which directories can contain sub-direction. In some file systems, file names are structured with a special syntax to extend file names and version numbers. In other files, names are simple lines, and the metadata on the file is stored elsewhere. Metadata Other accounting information is usually associated with every file in the file system. The length of the data contained in the file stored as the number of blocks allocated to the file, or as the exact number of cards. The last time the file was changed can be stored as a time stamp of the file. Some file systems also store the time a file is created, the time it last is accessed, and when the file metadata changes. (Please note that many early PC operating systems did not track file times.) Other information may include the type of file device (e.g. block, symbol, outlet, sub-direct, etc.), user ID and group ID, and access permission settings (e.g., whether the file is read only, running, etc.). Arbitrary attributes can be linked to advanced file systems such as XFS, /, some versions of UFS and HFS using advanced file attributes. This 33 34 34 feature is implemented in Linux, FreeBSD and Mac OS X operating systems and allows you to associate metadata with a file at the file level. This, for example, could be the author of a document, a symbol of encoding a simple text document, or checking. Hierarchical file systems was an early research interest of Dennis Ritchie of Unix fame; previous implementations were limited to only a few levels, such as IBM's implementations, even their early databases, such as IMS. Following the success of Unix, Ritchie extended the concept of the file system to each object in his later operating system developments, such as Plan 9 and Inferno. Traditional file systems offer opportunities to create, move, and delete files and directories. They lack the ability to create additional links to the directory (hard links to Unix), renaming parent links (..in UNix-like OS) and creating bidirectional links to files. Traditional file systems also offer opportunities to truncating, applying, creating, moving, deleting, and on-site to modify files. They do not offer pre-spending or truncation options from the beginning of the file, let alone an arbitrary insertion or deletion from the file. The operations provided are highly asymmetrical and have nothing in common to be useful in unexpected contexts. For example, unix interprocess pipes must be implemented outside the file system because the pipe concept does not offer consolidation from the beginning of the files. Secure Access 34 35 35 Secure Access to core file system operations can be based on a list scheme or access management capabilities. Studies have shown that access management lists are difficult to provide properly, so research operating systems tend to take advantage of opportunities. Commercial file systems still use access management lists. See: Secure computing types of file system types can be classified into disk file systems, network file systems, and special purpose file systems. Disc File Systems Disc File System presents if there were no files designed to store files on a storage device, most most disk that can be directly or indirectly connected to a computer. Examples of disk file systems are FAT (FAT12, FAT16, FAT32), NTFS, HFS and HFS, ext2, ext3, ISO 9660, ODS-5 and UDF. Some disk file systems are file systems or file system versions. is a flash file system file system designed to store files on flash memory devices. They are becoming more common as the number of mobile devices grows and flash memory capacity catches up with hard drives. While a block device layer can emulate the disk, so that the disk file system can be used on a flash device, it's suboptimal for several reasons: erasing blocks: Flash memory blocks must be clearly erased before they can be written. The time it takes to erase blocks can be significant, so it's useful to erase unused blocks during device downtime. 35 36 36 Random Access: Drive file systems are optimized to avoid drive tends when possible, due to the high cost of search. Flash memory devices don't delay search. Wear: Flash memory devices tend to wear out when one block is repeatedly rewritten; Flash file systems are designed to spread writes evenly. File systems, structured by a log, have all the desired properties for a flash file system. These file systems include JFFS2 and YAFFS. File Database Systems The new file management concept is the concept of a file system based on a database. Instead of hierarchical structured management, files are identified by their characteristics, such as file type, subject, author, or similar metadata. Transactional file systems Each disk operation can include changes in a number of different files and disk structures. In many cases, these changes are related, which means that it is important that they all run at the same time. Take, for example, a bank sending another bank money electronically. The bank's computer will send instructions for transfer to another bank, as well as update their own records to indicate that the transfer occurred. If for some reason the computer fails before it has been able to update its own records, then when reset, there will be no transfer records, but the bank will miss the money. Transaction processing ensures that at any time as it works, the transaction can be completed in its entirety or returned in its entirety (though not necessarily at any time). This means that if 36 37 37 malfunctions, or power failures after recovery, the storage condition will be consistent. (Either the money will be transferred or it will not be transferred, but it will never stay on the way.) This type of file system is designed to error-tolerance, but can incur additional overheads to do so. File logging systems are one of the methods used to implement level level transactions file-system structures. Network File Systems is a file system that acts as a client for a remote file access protocol, providing access to files on the server. Examples of network file systems are clients for NFS, AFS, SMB, and file system clients for FTP and WebDAV. Special special purpose file system systems are basically any file system that is not a disk file system or a network file system. This includes systems where files are located dynamically using software designed for purposes such as communication between computer processes or temporary file space. Special purpose file systems are most often used by file-oriented operating systems such as Unix. Examples include the procfs (/proc) file system used by some Unix variants, which provides access to information about processes and other functions of the operating system. Deep-sea research vehicles, such as Voyager 1 II, used special file systems based on digital tape. Most modern spacecraft, such as Cassini-Huygens, have used real-time operating system file systems or FILE systems under the influence of RTOS. 37 38 38 Mars Rovers are one such example of the RTOS file system, important in this case because they are implemented in flash memory. Crash counting is a feature of a file system developed as an alternative to logging. It is argued that it maintains consistency between failures without quoting the necessary complexity of the log implementation code. File systems and operating systems Most operating systems provide a file system, as the file system is an integral part of any modern operating system. The only real task of early microcomputer operating systems was to manage files, which is reflected in their names (see DOS). Some early operating systems had a separate file system processing component called the disk operating system. On some microcomputers, the disk's operating system was downloaded separately from the rest of the operating system. Early operating systems typically only support one, native, unnamed file system; for example, CP/M only supports its own file system, which, if necessary, can be called the CP/M file system, but which has no official name. Because of this, there must be an interface provided by the operating system software between the user and the file system. This interface can be textual (for example, provided by the interface strings such as the Unix shell, or OpenVMS DCL) or graphic (e.g. provided by a graphical user interface, such as file browsers). If graphic, a metaphor for a folder containing documents, other files and attachments are often used (see also: directory and folder). Flat file systems 38 39 39 In a flat file system there are no subdirections, everything is stored at the same (root) level on the media, be it hard drive, floppy disks, etc. this system quickly becomes inefficient as the number of files grows and makes it difficult for users to organize data into related groups. Like many small systems before it, the original Apple Macintosh featured a flat file system called the . His mac OS version was unusual in the sense that the Macintosh Finder created the illusion of a partially hierarchical filing system over MFS. This structure meant that each file on the disk had to have a unique name, even if it was in a separate folder. MFS was quickly replaced by a hierarchical file system that supported real directories. A recent addition to the amazon S3 flat file family, a remote storage service that is intentionally simplified to allow users to customize how their data is stored. The only designs are buckets (imagine an unlimited size drive) and objects (similar but not identical to the standard file concept). Pre-management of files allows you to use almost any symbol (including '/) in the name of objects, as well as the ability to select a subset of bucket contents based on identical prefixes. File systems under Unix-like operating systems Unix-like operating systems create a that makes all files on all devices appear to exist in the same hierarchy. This means that these systems have one root directory, and every file that exists in the system is somewhere beneath it. In addition, the root catalog should not be in any physical place. It may not be on your first hard drive - it may not even be on your computer. Systems similar to Unix can use the network's shared resource as a root directory. 39 40 40 unix-like systems assign the device's name to each device, but that's not how the files on that device are available. Instead, to access files on another device, you must first notify the operating system where in the catalog tree you would like these files to appear. This process is called file system installation. For example, to access files on CD-ROM, you need to tell the operating system: Take the file system from this CD-ROM and make it appear under such and such a directory. The catalog given to the operating system is called the attachment point - it can, for example, be /media. The catalog/media exists on many Unix systems (as stated in the Filesystem Hierarchy Standard) and is designed specifically for use as a anchorage point for removable media such as CDs, DVDs and floppy disks. It may be empty, or it may contain sub-direction to install individual devices. As a rule, only (i.e. root user) can authorize the installation of file systems. Unix-like operating systems often include software and tools that help with the installation process and provide it with new functionality. Some of these strategies invented auto-mounting as a reflection of their purpose. 1. In many situations, file systems other than root should be available as soon as the operating system is loaded. Thus, all systems similar to Unix ensure that file systems are installed during download. System administrators identify these file systems in a fstab or vfstab configuration file in the Solaris operating environment, which also indicates settings and attachment points. 2. In some situations, you don't need to mount certain file systems while downloading, although using them may be desirable after that. There are some utilities for Unix-like systems that allow the installation of predefined file systems on demand. 40 41 41 3. Removable media have become very common with microcomputer platforms. They allow programs and data to be transmitted between machines without a physical connection. Common examples include USB flash drives, CD-ROMs, and DVDs. Utilities were therefore designed to detect the presence and availability of the environment, and then mount that environment without any user intervention. 4. Progressive systems similar to Unix have also introduced a concept called super- mounting; See, for example, the Supermount-ng Linux project. For example, a floppy disk that has been installed can be physically removed from the system. Under normal circumstances, the drive had to be synchronized and then undone before it was removed. Provided that the synchronization occurred, another disk can be inserted into the disk. The system automatically notices that the disk has changed and updates the contents of the attachment point to reflect the new environment. Similar functionality is available on standard Windows machines. 5. A similar innovation preferred by some users is the use of autofs, a system that, like supermontation, eliminates the need for manual installation commands. The difference from super-apps, in addition to compatibility in a much larger range of applications, such as access to file systems on network servers, is that devices are installed transparently when requested on their file systems, as would be appropriate for file systems on network servers, rather than relying on events such as media insertion, as would be appropriate for a media shoot. Linux Linux file systems support many different file systems, but the overall choice for the system drive includes the ext family (such as ext2 and ext3), XFS, JFS and ReiserFS. Files under Mac OS X 41 42 42 Mac OS X uses a file system that he inherited from a classic Mac OS called HFS Plus. HFS Plus is a metadata-rich and file-saving system. Due to the unix roots of Mac OS X, Unix resolutions were added to HFS Plus. Later versions of HFS Plus added to prevent damage to the structure of the file system and introduced a number of optimizations into distribution algorithms in an attempt to automatically defragment the files files requires an external defragmentator. File names can be up to 255 characters. HFS Plus uses Unicode to store file names. On Mac OS X, the type of file may come from the type code stored in the file metadata or the file name. HFS Plus has three types of links: hard Links in the style of Unix, symbolic links in the style of Unix and aliases. Aliases are designed to keep a link to the original file, even if they are moved or renamed; they are interpreted not by the file system itself, but by the file manager's code in userland. Mac OS X also supports the UFS file system derived from the BSD Unix fast file system through NeXTSTEP. However, according to Mac OS X 10.5 (Leopard), mac OS X can no longer be installed on that UFS, nor can the pre-leopard system installed on the UFS volume be upgraded to Leopard. File systems according to Plan 9 from Bell Labs was originally designed to expand some of the good Unix points, and introduce some new ideas of their own, fixing the flaws of Unix. As for file systems, the Unix system treats things like files has been continued, but in terms of 9, everything is treated as a file, and access as a file will be (i.e. not ioctl or mmap). Perhaps surprisingly, while the file interface 42 43 43 made universal it is also greatly simplified, such as simlinks, hard links and suid outdated, and atomic creation/open operation is introduced. More importantly, a set of file operations becomes clearly defined and subversive activities of this as the ioctl is eliminated. Second, the 9P baseline protocol was used to eliminate the difference between local and deleted files (except for a possible delay difference). This has the advantage that the device or devices submitted by the files on a remote computer can be used as if it were your own device of a local computer (s). This means that under Plan 9, several file servers provide access to devices that class them as file systems. Servers for synthetic file systems can also work in the user space, bringing many benefits to micro-core systems while keeping the system simple. Everything in Plan 9 has an abstraction as a file; networks, graphics, debugging, authentication, capabilities, encryption, and other services are available through I-O operations on file handles. For example, it allows you to use the machine's IPlock stack without the need for a NAT, or provides a network of transparent window systems without the need for any additional code. Another example: Plan-9 receives the FTP service by opening the FTP website. The ftpfs processing server is open, essentially installing a remote FTP site as part of a local file system. With ftpfs as an intermediary, the app can now the usual file system operations to access the FTP site as if it were part of a local file system. Another example is the postal system that uses the file file that synthesize virtual files and directories to present a user's inbox as /mail/fs/mbox. Wikifs provides a file system interface for wikis. 43 44 44 These file systems are organized through private, in-place name space, allowing each process to have a different view of the many file systems that provide resources in the distributed system. The Inferno operating system shares these concepts with Plan 9. File systems under Microsoft Windows Windows uses file systems FAT and NTFS (New Technological File System). The File Distribution Table (FAT) application system, supported by all versions of Microsoft Windows, was an evolution of the system used in Microsoft's previous operating system (MS-DOS), which in turn was based on 86-DOS. FAT ultimately has its roots in the short-lived M-DOS project and the standalone BASIC drive in front of it. Over the years, various features have been added to it, inspired by similar features found in file systems used by operating systems such as Unix. Older versions of the FAT file system (FAT12 and FAT16) had limiting file name length, limiting the number of entries in the root catalog of the file system, and had limits on the maximum size of FAT-formatted discs or sections. Specifically, FAT12 and FAT16 had a limit of 8 characters for the file name and 3 characters for extension. This is commonly referred to as the 8.3 file name limit. VFAT, which was a continuation of FAT12 and FAT16, introduced in Windows NT 3.5 and subsequently included in Windows 95, allowed long file names (LFNs). FAT32 also considered many restrictions in FAT12 and FAT16, but remains limited compared to NTFS. The NTFS, presented with the Windows NT operating system, allowed ACL-control resolution. There are also strong links, multiple file streams, attribute indexing, quota of 44 45 45 tracking, compression, and attachment points for other file systems (so-called connections), although not all of these features are well documented. Unlike many other operating systems, Windows uses the abstraction of the letter of the disk at the user level to distinguish between one drive or section from another. For example, Path C: WINDOWS is a WINDOWS catalog on the section represented by the letter C. Disk C is most commonly used for the primary partition of the hard drive, which is usually installed on Windows and from which it is downloaded. This tradition became so firmly entrenched that errors occurred in older versions of Windows that made assumptions that the drive that the operating system was installed on was C. The tradition of using the letter C for the drive can be traced in MS-DOS, where the letters A and B were reserved for two flops. Network drives can also be to drive letters. The operating system calls the IFS () process. IFS calls the correct FSD (File System Driver) system) to open a selected file of four FSDs that work with different storage systems NTFS, VFAT, CDFS (for optical discs) and Network. FSD gets a location on the disk for the first file cluster from FAT (File Distribution Table), FAT98, VFAT (Virtual File Distribution Table), or, in the case of Windows XP, MFT (Master File Table). In short, the whole point of FAT, FAT98, VFAT, or MFT is to map out all the files on the disk and the records were they located (which track and sector the drive). Sharing files that allow users to share files raises a serious security issue. The general approach is to provide controlled access to files through a set of operations 45 46 46, such as reading, writing, deleting, listing and app. Then allow users to perform one or more operations. One of the popular protection mechanisms is the compressed version of the access list, where the system recognizes three classifications of users with each file and catalog: User Group others File system abstraction The quality of a good filing system - Maintainable - Full 46 47 47 - Secure - Available - Reliable - Readable - Expandable - Storage - Portable, etc. Storage files Discussion above describes the file as a concept presented by the user or the high-level operating system. However, any file that has any useful purpose, outside the thought of the experiment, must have some physical manifestations. That is, a file (abstract concept) in a real computer system should have a real physical analogue, if it should exist at all. Physically, most computer files are stored on a storage device. For example, there is a hard drive that most operating systems work from and where most of them store their files. Solid discs are the most common form of unstable storage in the early 21st century. Where files contain only temporary information, they can be stored in RAM. Computer files can be stored on a magnetic tape. Files can also be stored on other media in some cases, such as record CDs, digital universal drives, drives, USB flash drives, etc. Back up files When computer files contain information that is extremely important, the backup process is used to protect against disasters that can destroy files. Backing up files simply means creating copies of files in a separate location so they can be recovered if something happens to the computer, or if they are deleted accidentally. 47 48 48 There are many ways to back back files. Most computer systems provide useful programs to assist with the time of backup, can become very timeconsuming if there are a lot of files to protect. Files are often copied to removable media, such as wriggling compact files or cartridge tapes. Copying files to another hard drive on the same computer protects against the failure of one disk, but if necessary to protect against failure or or entire computer and then copies of the files must be made on other media that can be removed from the computer and stored in a safe, remote location. The Grandfather-Father-Son method automatically makes three backups, the grandfather file is the oldest copy of the file and the son of the current copy. File Media Warehouse is a device that can receive data and store it for later search. These devices cover a wide range of capacity and access speeds. Examples: Storage Controls 48 49 49 WEEK 4 THIS WEEK SPECIFIC LEARNING TO understand: Various methods of file organization in the computer file design system Alternative to 49 50 50 File Operations File Organization's Magnetic Storage Drive method is available in many forms, including floppy disks, hard drives, cartridges, exchanged multi-dish, and fixed drives. Below are concepts that apply differently to all of the above methods. A typical disk package consists of 6 discs held on the central spindle. Because the upper and lower parts are ignored by recording information, only 10 surfaces are used, each with 200 concentric recording tracks. The schematic view is shown in Figure 1. Each of the 200 tracks will be able to hold an equal amount of information, as it is a feature that is provided by special software (household), which is used in conjunction with the processing of disk files. When the device is in a position in the disk, the tracks are available to comb out 10 read/write heads held the hand of the assembly that moves between the drive and between it, as shown in the illustration. Thus, 10 tracks can be used without further movement of the heads once they are located above the first track. Therefore, for the sake of saving, they usually write on the cylinder of the data (see figure 1) and avoid unnecessary movement of heads. The disk package is loaded onto the disk and rotates at a normal speed of about 3,600 rpm when accessed. Each track can hold over 4,000 bytes. Sometimes the sectors on the drive are used in the same way with interblock gaps in the tape file, but in other cases they are ignored when it comes to data processing. Since this device has the ability to find the data area directly it is known as a direct access device and is popular for the versatility that it gives. 50 51 51 Direct Access Devices provide a storage facility that is a satisfactory trade-off between basic storage and magnetic tape. There are many ways to organize records on a disk or tape. The main methods of file organization used for files are: Serial serial index serial random (or direct) a. Serial files organizations are stored in chronological order, meaning that as each record is received, it is stored in the next available storage position. In B it is only used on a serial environment, such as magnetic tape. This type of file organization means that the records are not in a particular order and therefore, in order to get one entry, 51 52 52 the entire file must be read from start to finish. Serial organization is usually a method used to create transaction files (unsorted), work, and dump files. b. Consecutive sequences of Organization files are serial files whose records are sorted and stored in an upstream or descending field. The physical order of the records on the disk is not necessarily consistent, as most vendors support an organization where certain entries (inserted after the file is set up) are held in a logical sequence but are physically placed in the overflow area. They are no longer physically related to previous and next logical records, but they can be extracted sequentially. c. The indexed sequential organization indexed to a sequential file organization is logically the same as that of successive organizations, but the index is built with a block containing a record with that value for the key field. This method combines the benefits of a sequential file with the ability to directly access the main key (the main key is the field that is used to manage the sequence of records). These days, manufacturers that provide index sequential software allow you to build indexes using fields that are not off the main key. These additional indices are called Secondary Keys. There are three main index types: Basic Index: This provides location for each key that exists in the system. Implicit index: This type of index gives the location of all possible records (keys), whether they exist or not. 52 53 53 Limit Index: This index of record groups (keys) only provides the location of the highest key in the group. They usually form a hierarchical index. Data records are blocked before they are recorded on the disk. The index can consist of the highest key in each block (or on each track). In the example above, data records appear as 3 to a block. Thus, the index holds the key of the highest index in each block. (An essential element of an index that has been removed from the chart for simplicity is the physical address of the data record block).) If we want to access record 5, the key of which is A0038, we can quickly determine from the index that the record is m block 2, since this key is bigger than the highest key in block 1, A0025, and less than the highest key in block 2, A0053. As a result of the index we can go directly to the record we get, therefore, the term direct access. D. Accidental (or direct) 53 54 54 Randomly organized file contains records that are physically located without taking into account the sequence of the main key. Records are downloaded to the disk a direct link between the key of the record and its address in the file is usually using a formula (or algorithm) that converts the main key into the physical address of the disk. This link is also used for search. Using a formula (or algorithm) known as Key Transformation and there are several techniques that can be used: Division Taking Ratio Division Taking Remainder Truncation Folding Squaring Radix Conversion These techniques are often mixed to obtain a unique address (or location) for each entry (key). Producing the same address for two different records is known as synonym. Random files show a clear advantage where: Hit Rate is a low data can not be a package or sorted Fast response is required. Power to expand The normal trend of master files is to expand. Entries can be increased in size or can be added. Even if the total size or number of entries does not increase, changes will almost inevitably happen. Although 54,555 files on the disk are usually updated by overlay, add-ons should be provided and some reuseable storage tools arising from the deletion are desirable. The overflow arises from: i. Record assigned to the block, which is already filled. ii. The record is being expanded so that it can no longer be placed in the block. There are a number of power methods to expand: i. Indicating less than 100% of the pack density at the initial load. ii. Indication of the density of cylinder packaging is less than 100%. iii. Showing extension blocks (usually at the end of the file). The first method is effective and effective only if the extension is regular. Where localized expansion occurs to any degree, even in one block, this system will fail. The other two methods allow space for the first and second levels of overflow, respectively. Expansion blocks are used when all other overflow objects have been exhausted. Ideally, the first level overflow is located on the same cylinder as the overcrowded block, hence there is no fine incurred in terms of head movement. The second-level overflow usually consists of one or more blocks at the end of the file. If a significant amount of access to second-level overflow is made, the time time time will increase significantly. You need to reorganize the file to get the record back from the overflow. Each file organization can be accessed or processed differently, often combing through the benefits of one organization with the benefits of another. Summary of file organization and access methods: 55 56 56 Data transfer time from a direct storage device, such as a disk, can be calculated, but the formulas required for different types of file organizations vary. Examples of these formulas are as follows 56 57 57 57 58 58 For ransom or direct file organizations as seek time and delays between each records transferred transferred To be included: There may be multiple i/O disk requests at the same time. When you plan multiple disk queries, the total search time can be shortened. For example, the shortest time search in the first place. Стратегии планирования дисков, часто используемые стратегии включают (в дополнение к некоторым общим политикам планирования процессора): First Come First Served (FCFS) или FIFO Shortest Service Time First (SSTF) SCAN туда и обратно по круговому SCAN диска C-SCAN или в одну сторону SCAN и быстрое возвращение LOOK искать запрос, прежде чем двигаться в этом направлении C-LOOK круговой LOOK Файл распределения файлов файловая система выделяет дисковое пространство, когда файл создан. With a lot of files living on the same drive, the main problem is how to allocate space for them. The file distribution scheme affects the efficient use of disk space and file access time. General File Distribution Methods: Related Chain (Related) Indexed All of these methods highlight the disk space based on the block (the smallest address drive). 59 60 60 Related Distributions Highlight drive space as on a page segmented memory. Keep a free list of unused disk space. Benefits: Easy access, both sequential and occasional simple few looking for flaws: external fragmentation may not know the in advance of the Chained (related) distribution of space similar to the distribution of page frames. To separate the allocated blocks as incredible. Benefits: No external fragmentation files can easily grow Flaws: many looking for random access are a difficult example: the MSDOS (FAT) file system. 60 61 61 Indexed Distribution Highlight the array of pointers when creating the file. Fill in the array when new disk blocks are allocated. Benefits: A small internal fragmentation of easily sequential and direct access disadvantages: a lot tends if the file is a large maximum file size is limited to the size of the sample block: the . Free space management Because the amount of disk space is limited (creates a management problem similar to a physical memory problem), you need to reuse the space released by deleted files. Typically, file systems keep a list of free disk blocks (originally all blocks are free) and manage this list with one of the following methods: Bit vectors 61 61

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