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Ass#1 (cs3112 os)


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Ass#1 (cs3112 os)

  1. 1. <ul><li>Machine Cycle Definition</li></ul>A machine cycle, also called a processor cycle or a instruction cycle, is the basic operation performed by a central processing unit (CPU). A CPU is the main logic unit of a computer. A machine cycle consists of a sequence of three steps that is performed continuously and at a rate of millions per second while a computer is in operation. They are fetch, decode and execute. There also is a fourth step, store, in which input and output from the other three phases is stored in memory for later use; however, no actual processing is performed during this step. In the fetch step, the control unit requests that main memory provide it with the instruction that is stored at the address (i.e., location in memory) indicated by the control unit's program counter. The control unit is a part of the CPU that also decodes the instruction in the instruction register. A register is a very small amount of very fast memory that is built into the CPU in order to speed up its operations by providing quick access to commonly used values; instruction registers are registers that hold the instruction being executed by the CPU. Decoding the instructions in the instruction register involves breaking the operand field into its components based on the instructions opcode. Opcode (an abbreviation of operation code) is the portion of a machine language instruction that specifies what operation is to be performed by the CPU. Machine language, also called machine code, refers to instructions coded in patterns of bits (i.e., zeros and ones) that are directly readable and executable by a CPU. A program counter, also called the instruction pointer in some computers, is a register that indicates where the computer is in its instruction sequence. It holds either the address of the instruction currently being executed or the address of the next instruction to be executed, depending on the details of the particular computer. The program counter is automatically incremented for each machine cycle so that instructions are normally retrieved sequentially from memory. The control unit places these instructions into its instruction register and then increments the program counter so that it contains the address of the next instruction stored in memory. It then executes the instruction by activating the appropriate circuitry to perform the requested task. As soon as the instruction has been executed, it restarts the machine cycle, beginning with the fetch step. <br />Word Size<br />The word size used in a computer is generally limited to an economical size but involves the memory size, Size of the instruction set, and precision put required in the computer.<br />Memory Size<br />The number of bits required to address the number of memory locations must be taken into account in setting the computer word size. While systems can be built which use multiple words or selected word parts to contain a memory address, this usually leads to involved addressing equipment and adds to the cost or running time of the machine.<br />Instruction Count<br />The word size must be large enough to accommodate the number of instructions which are required to do the things that are required of the machine. There are all kinds of possible processing jobs which may be made part of a computer these special instructions can lead to oversize and expensive computers. One extreme example of this is a computer which had a record gather and a record scatter instruction couplet. This is useful for working with records to be sorted and made up into reports, but was of little use for my scientific computations. On the other hand, I would have liked to have a square root instruction for my scientific work. How ever the instruction set size must be taken into account in setting a computer's word size. HYPERLINK "" l " si" Go to Special Instructions<br />Data Precision<br />The required data precision is of primary concern when establishing word size. Present day practice limits word size to multiples of eight bit byte sizes by the convention established to drive printers and other output devices. Early computers used as little as six bits for storage of alphabetic information and consequently had multiples of six bit word sizes. Other formats are possible, such as BCD method of storing all numbers in floating point form as was used by the ATARI home computer which storedall numbers with a ten digit format and with a power of ten exponent. Common specifications to day lead to a word size of 32 bits or 64 bits for very high precision. Smaller word sizes may be used for specific purposes.<br />Computer architecture<br />In computer engineering, computer architecture is the conceptual design and fundamental operational structure of a computer system. It is the technical drawings and functional description of all design requirements (especially speeds and interconnections), it is how to design and implement various parts of a computer — focusing largely on the way by which the central processing unit (CPU) operates internally and how it accesses addresses in memory.<br />It can be defined as the science and art of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals.<br />Computer architecture is the theory behind the design of a computer. In the same way as a building architect sets the principles and goals of a building project as the basis for the draftsman's plans, so too, a computer architect sets out the computer architecture as a basis for the actual design specifications. <br />There are several usages of the term, which can be used to refer to: <br />The design of a computer's CPU architecture, instruction set, addressing modes, and techniques such as SIMD and MIMD parallelism. <br />More general wider-scale hardware architectures, such as cluster computing and Non-Uniform Memory Access (NUMA) architectures. <br />The less formal usage refers to a description of the requirements (especially speeds and interconnection requirements) or design implementation for the various parts of a computer. (Such as memory, motherboard, electronic peripherals, or most commonly the CPU.) <br />Architecture is often defined as the set of machine attributes that a programmer should understand in order to successfully program the specific computer (i.e., being able to reason about what the program will do when executed). For example, part of the architecture are the instructions and the width of operands manipulated by them. Similarly, the frequency at which the system operates is not part of the architecture. This definition reveals the two main considerations for computer architects: (1) Design hardware that behaves as the programmers think it should. (2) Utilize existing implementation technologies (e.g., semiconductors) to build the best computer possible (best can be defined in many different ways as described in Design Goals). The latter consideration is often referred to as microarchitecture. <br /><ul><li>Motherboard</li></ul>A motherboard is the central printed circuit board (PCB) in many modern computers and holds many of the crucial components of the system, while providing connectors for other peripherals. The motherboard is sometimes alternatively known as the main board, system board, or, on Apple computers, the logic board.[1] It is also sometimes casually shortened to mobo.<br />slot<br /> A receptacle for additional printed circuit boards.<br /> A receptacle for inserting and removing a disk or tape cartridge.<br /> In communications, a narrow band of frequencies. See time slot.<br /> May refer to reserved space for temporary or permanent storage of instructions, data or codes.<br />Computer bus<br />In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers. Unlike a point-to-point connection, a bus can logically connect several peripherals over the same set of wires. Early computer buses were literally parallel electrical buses with multiple connections, but the term is now used for any physical arrangement that provides the same logical functionality as a parallel electrical bus. Modern computer buses can use both parallel and bit-serial connections, and can be wired in either a multidrop (electrical parallel) or daisy chain topology, or connected by switched hubs, as in the case of USB. <br />Computer network<br />A computer network, often simply referred to as a network, is a collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of types and categories and also presents the basic components of a network.<br />signal<br />An electromagnetic impulse or wave transmitted to convey information in telecommunications, telegraphy, television, radio, radar, etc.<br />Any electrical or light pulse or frequency whether in a wire or fiber or wireless. The term is somewhat generic and may refer to virtually anything that is generated and transmitted (power, data, control signals). Although the term may be used by itself later on in a description or article, it is often used at least initially with another word, such as " carrier signal," " data signal" or " control signal." See signal-to-noise ratio and control signal.<br />Local area network<br />A computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN). <br />Most LANs connect workstations and personal computers. Each node (individual computer ) in a LAN has its own CPU with which it executes programs, but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to HYPERLINK "" " undefined" communicate <br />with each other, by sending e-mail or engaging in chat sessions. <br />Wide area network<br />A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs). <br />Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet. <br />network server<br />A computer system that serves as a central repository of data and programs shared by users in a network. A device that functions as an access control point for users in remote locations connecting to a company's internal network or to an ISP. Also called a " media gateway" or a " remote access server" (RAS), a network access server (NAS) may include its own authentication services or rely on a separate authentication server. A NAS may be a dedicated server or a software service within a regular server.<br />workstation<br /> A high-performance, single-user computer typically used for graphics, CAD, software development and scientific applications. A workstation may be a RISC-based computer that runs under some version of Unix or Linux, the major vendors being Sun, HP, IBM and SGI. It may also refer to a high-end PC using Intel or AMD CPUs from any PC vendor. In all cases, the term implies a machine with a fast CPU and large amounts of memory and disk that is geared toward the professional user rather than the consumer.<br /> A terminal or desktop computer in a network. In this context, workstation is just a generic term for a user's machine (client machine) in contrast to a " server" or " mainframe." <br /> In the telecom industry, a combined telephone and computer.<br /> host<br />The central computer in a mainframe or midrange computer environment to which the networks and terminals connect. See also computer, mainframe computer, midrange computer, network, and terminal. <br />In telecommunications, local area networks (LANs), and networks, in general, a server that functions to provide programs or data files to client computers. See also client, LAN, telecommunications, network, and server. <br />In the Internet, any computer that can serve as a source or destination for data transfers.An Internet host has a unique Internet Protocol (IP) address and unique domain name. See also domain, Internet, and IP.<br /> 5.Network topology<br />Network topology defines the physical layout of a network environment. Network topology involves cabling, client computers, routers and hubs. The network topology does not include the logical topology, which is the protocols used to communicate between computers. However, the physical layout of machines and devices plays a role in how the protocols are set up. <br />