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 Bit:... 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 bits Alternative Words WEEK 2 WEEK 3 Identification and File File System 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 Microsoft Windows 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 Linux 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, byte 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 bytes. 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 file manager 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 kilobit (kb) kibibit (Kibit) 2 10 megabits (Mbit) mebibit (Mibit) 2 20 gigabit (Gbit) gibit (Gibit) 2 30 tera (Tbit) tebibit (Tibit) 2 40 petabit (Pbit) pebibit (Pibit) 2 50 exabit (Ebit) exbibit (Eibit) 2 60 zettabit (sbit) zebibit (Sibit) 2 70 yottabit (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 flash memory, 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.