Cpu (central processing unit)

This unit, called the processor, controls the order in which the computer deals with information. Computer software consists of programs or information fed into the computer. This processor also does all the counting, makes all the logical decisions and helps the computer parts to work together.

A CPU is a small wafer of silicon, called a 'chip' only l/8th of an inch square, and l/100th of an inch thick. Since the actual chip is so small, it is embedded in a black plastic slab called a DIP (Dual Inline Package) that has connectors built into its edges. The connectors, called pins, plug into the main circuit board of the system unit, and carry data to and from the CPU.

A chip called the interpreter changes BASIC words into special numbers, called binary numbers. Other chips may make sounds and pictures.

The processor has to perform two main types of functions: arithmetic and control. For these tasks, the CPU has 2 functional parts - a ALU (Arithmetic and Logic Unit) and a CU (Control Unit). The ALU contains the circuits and special storage locations used to perform mathematical operations. CU is the control unit which keeps the processing in progress, moving from one instruction to another as the program requires. It also initiates and stops input and output operations, and moves data between the store and the ALU.

MEMORY

All computers have a memory. They remember facts and instructions. There are computer chips which cannot do any computing function, but only store information. They are called memory chips.

Memory is measured in bits and bytes. All information, fed into the computer is changed into digits or numbers called binary numbers. The binary system uses only two digits; 0 and 1. These digits are called bits. Different combinations of bits represent letters, symbols, and decimal numerals. Each such combination of bits is called a byte. There are two kinds of memory chips in most of the PCs.

RAM (RANDOM ACCESS MEMORY)

This can also be read as Removable Any Minute memory. It is that area of the main memory where information can be written in and read from. When a program is read off a disk, it is written into RAM. But, RAM stores information only while the computer is on. Once it is turned off, all data stored in it is lost. For data consisted in RAM requiring storage, copies have to be made -either on another floppy or on the hard disk. Information in RAM can be put on the tape very easily often by just typing SAVE on the keyboard. When the information is needed again, it can be brought from the tape into the computer's RAM, often by just typing LOAD.

The 3 main characteristics of RAM:

• It provides both reading and writing ability

• It permits the recording of new information over previously stored data

• Its access time is independent of the sequence in which bits of information was recorded.

A PC can have between 64 Kb to 640 Kb of RAM in it. Memory size is expressed as a power of 2.

Since 2¹⁰ = 1024, so 1 Kb = 1024 bytes. A computer with 64 Kb of RAM is said to have storage space for 64,000 bytes of information, but actually that RAM would hold 65,536 bytes (64 x 1024).

Can you work this out?

How many bytes are needed to store this? Connaught Place

Ans: 15

[You even count the blank space between the words.] Extra RAM can be added to the PC by either plugging in another bank of chips into the main circuit board or by adding an extra circuit board with RAM chips in one of the PC's five expansion slots.

ROM (READ ONLY MEMORY)

This area of memory can only be read from and not written into. The 2 main characteristics of ROM memory are: