System Unit and CPU

A system unit is the main body of a computer, typically consisting of a plastic or metal enclosure and the motherboard, which is the central or primary circuit board that makes up a computer system or other complex electronic system. It often includes a power supply, cooling fans, internal drives, and the circuit boards that are plugged into the motherboard, such as video and network cards. A printed circuit board (PCB) interconnects electronic components without discrete wires. Alternative names are printed wiring board (PWB). There are also buttons, indicators, different ports and plug-and-sockets.

Manufacturers and retailers of desktop computers often erroneously describe the computer case and its contents as the CPU, which is misleading. Thus, the system unit is occasionally referred to as the CPU, though this really means central processing unit.

Central processing unit (CPU, processor) is the part of a computer, which controls all the other parts, interprets and carries out the instructions contained in the software. Designs vary widely but, in general, the CPU consists of the control unit, the arithmetic and logic unit (ALU) and memory (registers, cache, RAM and ROM) as well as various temporary buffers and other logic.

A control unit is the part of a CPU or other device that directs its operation. The outputs of the unit control the activity of the rest of the device.

The ALU performs mathematical calculations and logical operations.

Usually, a collection of registers is included to hold operands and intermediate results. The registers are high-speed memory units used to store and control information. One of these registers is the program counter (PC) which keeps track of the next instruction to be performed in the main memory. Another is the instruction register (IR), which holds the instruction that is currently being executed.

The term CPU is often used vaguely to include other centrally important parts of a computer such as caches and input/output controllers, especially in computers with modern microprocessor chips that include several of these functions in one physical integrated circuit.

In computer science, a cache is an easily accessible memory used to store a subset of a larger pool of data that is expensive or slow to either fetch or compute. Repeated accesses to the data can reference the cache rather than refetching or recomputing, so that the perceived average access cost or time is lower.

A microprocessor (abbreviated as µP or uP) is an electronic computer CPU made from miniaturized transistors and other circuit elements on a single semiconductor IC (AKA chip). Before the advent of microprocessors, electronic CPUs were made from discrete (separate) transistors; and before that, from vacuum tubes. An IC is a microelectronic semiconductor device consisting of many interconnected transistors and other components.

One area where microprocessors differ is in the amount of data – the number of bits – they can work with at a time. There are 8, 16, 32 and 64-bit and higher processors. The computer’s internal architecture is evolving so quickly that the 64-bit processors are able to address 4 billion times more information than a 32-bit system.

The programmes and data, which pass through the central processor must, be loaded into the main memory (also called the internal memory) in order to be processed. Thus, when the user runs an application, the microprocessor looks for it on secondary storage devices (disks) and transfers a copy of the application into the RAM area. RAM is temporary, i.e. its information is lost when the computer is turned off. However, the ROM section is permanent and contains instructions needed by the processor.

The power and performance of a computer is partly determined by the speed of its microprocessor. A clock provides pulses at fixed intervals t to measure and synchronize circuits and units. The clock speed is measured in MHz or GHz (megahertz or gigahertz) and refers to the frequency at which pulses are emitted. For example, a CPU running at 3 GHz (3x10⁹ cycles per second) is likely to provide a very fast processing rate and will enable the computer to handle the most demanding applications.

9. Answer the questions.

1) What is system unit and what does it include? 2) What is CPU and what does it consist of? 3) What does the CPU do? 4) What is a control unit and what is its task? 5) What are registers? 6) What is cache? 7) What can reference the cache? 8) What is a microprocessor? 9) What were electronic CPUs made from? 10) What is the difference of microprocessors? 11) What does the microprocessor look for when you run an application? 12) How is power and performance of a computer measured? 13) What does the clock provide? 14) What is the measure unit of the clock speed?

10. Read this passage about the structure of the processor and fill in the gaps using the words below.

Дата добавления: 2015-07-20