Text 3 Central Processing Unit
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At the centre of the computer system is the CPU, which can be considered to be the “brain” of the computer. Its main components are the central processor and the main memory. The speed and capacity of these components have been greatly improved with each new generation of computers. In the first generation, the central processor was built from electronic valves, which were rather unreliable. The second generation used transistors. The third generation used integrated circuits. The fourth generation of computers uses microprocessors. These are contained on electronic chips, which are slices of silicon with thousands of electronic components and circuits engraved on them.
Early computers used magnetic cores in their main memory but fourth generation computers use much smaller and more powerful electronic memory chips.
The two parts of the central processor are the Control Unit (CU) and the arithmetic and Logic Unit (ALU).
The control unit controls all other units in the computer system. It decodes the program instructions and makes sure they are carried out in the correct sequence. The arithmetic and logic unit, on the other hand, performs the calculations and data manipulation e.g. comparing, sorting and combining data.
These units have small, short-item storage areas called registers, which are used for special tasks. For example, the register in the CU known as the program computer is used to hold the address of the next instruction to be carried out. The register in the ALU known as the accumulator is used to temporarily hold the data item currently being processed.
Each unit of the CPU is connected by a group of wires called a bus. There are data buses for carrying data from one unit to another, control buses for sending control signals to each unit and address buses for accessing each part of the main memory.
The power of CPU is partly determined by its speed. This is controlled by a clock in the processor, which sends out regular pulses to each unit to keep them in step. The clock pulse rate is measured in megahertz (MHz).
Text 4 Basic Software
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Information provided by programs and data is known as software. Programs are sets of instructions that make the computer execute operations and tasks. There are two types of software:
-- The system software refers to all the programs which control the basic functions of a computer. They include operating systems, system utilities (e.g. an anti-virus program, a back-up utility) and language translators (e.g. a compiler – the software that translates instructions into machine code).
-- The applications software refers to all those applications – such as word processors and spreadsheets – which are used for specific purposes. Applications are usually stored on disks and loaded into the RAM memory when activated by the user.
The operating system is the most important type of system software. It is usually supplied by the manufacturers and comprises a set of programs and files that control the hardware and software resources of a computer system. It controls all the elements that the user sees, and it communicates directly with the computer. In most configurations, the OS is automatically loaded into the RAM section when the computer is started up.
System utilities are small programs which improve a system’s performance and help users take advantage of the computer’s capabilities. They are often desk accessories that can be called up while you’re working in another application. They can also be INITs – i.e. system extensions which are activated when you turn on the computer; control devices which you adjust in the control panel, or even stand-alone programs that run when you need them. Utilities are available for back-up, file search, virus protection, disaster recovery, and so on.
Spreadsheets* are application programs for financial planning which allow the user to analyse information presented in tabular form, by manipulating rows and columns.
* spreadsheet – электронная таблица