Central Processing Unit

The CPU will work through a set of instructions to process data. The instructions and data that the CPU is working on will be stored in the CPU's memory store, normally having been copied to the memory from backing storage. The way in which the CPU works through the instructions is becoming increasingly complex as processor design advances but various factors can be used to indicate how powerful a particular processor is.

All processors depend on a series of pulses or clock signals to control the internal movement and processing of data. In general the faster the clock speed is (measured in megahertz MHz) the faster the processor will be able to process data. A typical microprocessor would have a clock speed of around 350 MHz

The size of the associated memory store will also affect processor performance. A larger store will allow more data to be present in memory and therefore available for immediate processing. There will then be fewer delays while the processor waits for data to be copied from backing store. A larger memory also allows the processor to have several different programs or tasks available in central memory at the same time. Memory is measured in megabytes (MB). A byte is a group of binary digits (bits) used to encode a character. In practice, when dealing with memory this is invariably 8 bits. 210 bytes (1024) is called a kilobyte (KB) and a MB is 1024 KB. It would be usual for a microprocessor to have around 256 MB of memory although systems where speed of processing is important, such as graphical applications, would probably have 1 GB or more. Please note the most up-to-date specs will be in the buying a computer section of this site

The memory is made up of two types of memory chip. Read only memory (ROM) contains data that is stored in the chip when it is manufactured. This data cannot be changed and it remains permanently stored in the chip. Normally the memory will contain a small amount of ROM to store the bootstrap loader program. This is the program that sets the computer up when it is first switched on. Its main task is to load the operating system - the program that runs the computer system - as part of the power up sequence. The alternative to ROM is Random Access Memory (RAM) which is used to store data loaded into the memory from the backing store - i.e. the data that the computer is to process. When the computer is turned off, any data stored in RAM is lost.

The processor unit will normally consist of a set of circuit boards plugged in to a central case. Its performance can be enhanced by adding boards for specialised purposes such as performing arithmetic or controlling a graphics display. The main difference between a microcomputer and the more powerful mini and mainframe computers is that the latter have a number of different boards, each devoted to one aspect of the CPU's role. A microcomputer is based on a microprocessor chip that replaces several of these individual boards. Even in a basic microcomputer there will be scope to plug in additional boards and memory to increase the power of the system.

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