Task 7. Read the text, name other important elements of a computer system which have not been mentioned yet. Give definitions.

What's inside a PC system?

The nerve centre of a PC is the processor, also called the CPU, or central processing unit. This unit is built into a single microprocessor chip which executes program instructions and coordinates the activities that take place within the computer system. The chip itself is a small piece of silicon with a complex electrical circuit called an integrated circuit.

The processor consists of three main parts.

· The control unit examines the instructions in the user's program, interprets each instruction and causes the circuits and the rest of the components – disk drives, monitor, etc. - to execute the functions specified.

· The arithmetic logic unit (ALU) performs mathematical calculations (addition, subtraction,
division, etc.) and logical operations (AND, OR, NOT, etc.).

· The registers are high-speed units of memory used to store and control information. One of these registers is the program counter which keeps track of the next instruction to be performed in the main memory. The other is the instruction register which holds the instruction that
is currently being executed.

The power and performance of a computer is partly determined by the speed of its microprocessor. A system clock sends out signals at fixed intervals to measure and synchronize the flow of data. Clock speed is measured in GHz (gigahertz) and refers to the frequency at which signals are sent. For example, a CPU running at 4 GHz (four thousand million cycles per second) will enable the computer to handle the most demanding applications.

RAM and ROM

The programs 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. Therefore, when the user runs an application, the CPU looks for it on the hard disk and transfers a copy of the application into the RAM area. RAM (random access memory) is volatile or temporary, i.e. its information is lost when the computer is turned off. If we want to use this data later, we have to save it on disk. RAM capacity can be expanded by adding extra chips, usually contained in small circuit boards called dual in-line memory modules (DIMMs). The size of RAM is vital when various programs are opened simultaneously or when a file is very complex.

However, the ROM section (read only memory) is non-volatile or permanent and contains instructions for the basic operations. These are used to start up the computer, to read the data from the keyboard or to send characters to the screen. The BIOS (basic input/output system) uses ROM to control communication with peripherals.

Buses and cards

The main circuit board inside the system is called the motherboard and contains the processor, the memory chips, expansion slots and controllers for peripherals, connected by buses – electrical channels which allow devices inside the computer to communicate with each other. For example, the front side bus carries all data that passes from the CPU to other devices.

The size of a bus, called bus width determines how much data can be transmitted. It can be compared to the number of lanes on a motorway – the larger the width, the more data can travel along the bus. For example, a 64-bit bus can transmit 64 bits of data.

Most of today's computers have expansion slots that allow users to install adapters or expansion cards adding features like sound, memory and network capabilities.