Unit 1 (Chapter 1 & 2.) Key Concepts and Topics: Central Processing Unit Multi-programming Data fetch cycle The CPU is the part of a computer system that is commonly referred to as the "brains" of a computer. The CPU is also known as the processor or microprocessor and is responsible for executing a sequence of stored instructions called a program. Multitasking has the same meaning of multiprogramming but in a more general sense, as it refers to having multiple: programs, processes, tasks, threads; running at the same time. This term is used in modern operating systems when multiple tasks share a common processing resource (e.g., CPU and Memory). An instruction cycle (sometimes called a fetch–decode–execute cycle) is the basic operational process of a computer. It is the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction dictates, and carries out those actions. Memory and RAM, DRAM Job pool and Job scheduling File DRAM is a type of memory that is typically used for data or program code that a computer processor needs to function. DRAM is a common type of RAM used in personal computers (PCs), workstations and servers. Random access allows the PC processor to access any part of the memory directly rather than having to proceed sequentially from a starting place. RAM is located close to a computer’s processor and enables faster access to data than storage media such as hard disk drives and solid-state drives. The concept of “job pool” refers to a batch processing system, where jobs are queued to be executed when resources are available. The job pool contains both jobs that are currently executing and jobs that have been scheduled but are not yet being executed. ... When a job is executing, it is fully present in memory. Job scheduling is the process of allocating system resources to many different tasks by an operating system (OS). The system handles prioritized job queues that are a-waiting CPU time and it should determine which job to be taken from which queue and the amount of time to be allocated for the job. A collection of data or information that has a name, called the filename. Almost all information stored in a computer must be in a file. There are many different types of files: data files, text files, program files, directory files, and so on. ... For example, program files store programs, whereas text files store text. A collection of data on a computer constitutes a FILE. Firmware, ROM, EEPROM Time sharing or multitasking Mass storage Firmware is programming that's written to a hardware device's nonvolatile memory ROM. Hardware makers use embedded firmware to control the functions of various hardware devices and systems, much like a computer's operating system (OS) controls the function of software applications. EEPROM (electrically erasable programmable read-only memory) is user-modifiable read-only memory (ROM) that can be erased and reprogrammed (written to) repeatedly through the application of higher than normal electrical voltage. Unlike EPROM chips, EEPROMs do not need to be removed from the computer to be modified. However, an EEPROM chip has to be erased and reprogrammed in its entirety, not selectively. It also has a limited life - that is, the number of times it can be reprogrammed is limited to tens or hundreds of thousands of times. In an EEPROM that is frequently reprogrammed while the computer is in use, the life of the EEPROM can be an important design consideration. Time-sharing is a technique which enables many people, located at various terminals, to use a particular computer system at the same time. Time-sharing or multitasking is a logical extension of multiprogramming. Processor's time which is shared among multiple users simultaneously is termed as time-sharing. Mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. Input / Output (I/O) devices Interactive computer system Caching I/O (input/output), pronounced "eye-oh," describes any operation, program, or device that transfers data to or from a computer. Typical I/O devices are printers, hard disks, keyboards, and mice. In fact, some devices are basically input-only devices (keyboards and mice); others are primarily output-only devices (printers); and others provide both input and output of data (hard disks, diskettes, writable CD-ROMs). In computer science, interactive computing refers to software which accepts input from humans as it runs. Interactive software includes most popular programs, such as word processors or spreadsheet applications. Caching is a very general technique for improving computer system performance. Based on the principle of locality of reference, it is used in a computer's primary storage hierarchy, its operating system, networks, and databases. Instruction-Execution Cycle Response time Cache management An instruction cycle (sometimes called a fetch–decode–execute cycle) is the basic operational process of a computer. It is the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction dictates, and carries out those actions. The elapsed time between the end of an inquiry or demand on a computer system and the beginning of a response; for example, the length of the time between an indication of the end of an inquiry and the display of the first character of the response at a user terminal. Introduction to Cache Management. The cache provides in-memory storage and management for your data. You organize your data in the cache into data regions, each with its own configurable behavior. You store your data into your regions in key/value pairs called data entries. Instruction Register Process I/O subsystem In computing, an instruction register (IR) is the part of a CPU's control unit that holds the instruction currently being executed or decoded. A process is an instance of a program running in a computer. It is close in meaning to task, a term used in some operating systems. In UNIX and some other operating systems, a process is started when a program is initiated (either by a user entering a shell command or by another program). The I/O subsystem is connected to the rest of the components. It is in-charge of interacting with all of the devices that are responsible for either: entering information into the system or used to store or show information coming from the system. Storage Device Hierarchy Virtual memory Protection A storage device hierarchy consists of a group of storage devices that have different costs for storing data, different amounts of data stored, and different speeds of accessing the data. Virtual memory is a memory management capability of an OS that uses hardware and software to allow a computer to compensate for physical memory shortages by temporarily transferring data from random access memory (RAM) to disk storage. Virtual address space is increased using active memory in RAM and inactive memory in hard disk drives (HDDs) to form contiguous addresses that hold both the application and its data. Protection, then, is any mechanism for controlling the access of processes or users to the resources defined by a computer system. This mechanism must provide means to specify the controls to be imposed and to enforce the controls. Protection can improve reliability by detecting latent errors at the interfaces between component subsystems. SCSI Swapping Security The Small Computer System Interface (SCSI) is a set of parallel interface standards developed by the American National Standards Institute (ANSI) for attaching printers, disk drives, scanners and other peripherals to computers. SCSI (pronounced "skuzzy") is supported by all major operating systems. A process must be in memory to be executed. A process, however, can be swapped temporarily out of memory to a backing store and then brought back into memory for continued execution. Swapping makes it possible for the total physical address space of all processes to exceed the real physical memory of the system, thus increasing the degree of multiprogramming in a system. Security protects the integrity of the information stored in the system, from unauthorized access, malicious destruction or alteration and accidental introduction of inconsistency. Direct Memory Access Interrupt driven Network OS Direct memory access is used for high-speed I/O devices in order to avoid increasing the CPU’s execution load. If the CPU does not poll the control bit, but instead receives an interrupt when the device is ready for the next byte, the data transfer is said to be interrupt driven. A network operating system is an operating system that provides features such as file sharing across the network, along with a communication scheme that allows different processes on different computers to exchange messages. Device Driver Trap or exception Real-time OS The device controller is responsible for moving the data between the peripheral devices that it controls and its local buffer storage. Typically, operating systems have a device driver for each device controller. This device driver understands the device controller and provides the rest of the operating system with a uniform interface to the device. A trap (or an exception) is a software-generated interrupt caused either by an error (for example, division by zero or invalid memory access) or by a specific request from a user program that an operating-system service be performed. The interrupt-driven nature of an operating system defines that system’s general structure. A is used when rigid time requirements have been placed on the operation of a processor or the flow of data; thus, it is often used as a control device in a dedicated application. Multiprocessor System (Parallel system) Dual-mode Hand-held System Such systems have two or more processors in close communication, sharing the computer bus and sometimes the clock, memory, and peripheral devices.