Central Processing Unit – CPU
The central processing unit (CPU), also called the microprocessor, the processor or central processor is the brains of the computer. The CPU is housed on a tiny silicon chip. This chip contains millions of switches and pathways that help your computer make important decisions. The switches control the flow of the electricity as it travels across the miles of pathways. The CPU knows which switches to turn on and which to turn off because it receives its instructions from computer programs. Programs are a set of special instructions written by programmers that control the activities of the computer. Programs are also known as software
The CPU has two primary sections:
• Control Unit
• Arithmetic/Logic Unit
Because all computer data is stored as numbers, a lot of the processing that takes place involves comparing numbers or carrying out mathematical operations. In addition to establishing ordered sequences and changing those sequences the computer can perform only two types of operations: arithmetic operations and logical operations. Arithmetic operations include addition, subtraction, multiplication and divisions. Logical operations include comparisons, such as determining whether one number is equal to, greater than or less than another number. Also, every logical operation has an opposite. For example, in addition to “equal to” there is “not equal to.”
Many instructions carried out by the control unit involve simply moving data from one place to another – from memory to storage, from memory to the printer and so forth. However, when the control unit encounters an instruction that involves arithmetic or logic, it passes that instruction to the second component of the CPU, the arithmetic or logic unit, or ALU. The ALU includes a group of registers – high-speed memory locations built directly into the CPU that are used to hold the data currently being processed. For example, the control unit might load two numbers from memory into the registers in the ALU. Then, it might tell the ALU to divide the two numbers (an arithmetic operation) or to see whether the numbers are equal (a logical operation).
Types of Computer Bus
There are two main buses in a computer:
Data Bus Address Bus
The data bus is an electrical path that connects the central processing unit (CPU) memory, and the other hardware devices on the motherboard. Actually, the bus is a group of parallel wires. The number of wires in the bus affects, the speed at which data can travel between components, just as the number of lanes on a highway effects how long it takes people to get to their destinations. Because each wire can transfer one bit at a time, an eight-wire bus can move eight bits at a time. A 16-bit bus can transfer two bytes and a 32-bit bus can transfer four bytes at a time.
The second bus that is found in every micro computer is the address bus. The address bus is a set of wires similar to the data bus, but is connects only the CPU and memory and all it carries are memory addresses. The reason that the address bus is important is that the number of lines in it determines the maximum number of memory address. For example, one byte of data is enough to represent 2 = 256 different values, if the address bus could carry only eight bits at a time, the CPU could address only 256 bytes of memory. Most of the early PCs had 20-bit addres bus, so the CPU could address only 2(20) bytes or 1 MB of data.
A system board with its processor and memory unit can work only when linked to input/output storage and communication devices to receive data and communicate results of processing. Peripheral devices such as a keyboard, mouse, monitor and a printer come with a cable and a multiple connector. To link a device to the PC, you plug its connector into a receptacle called a port in much the same way you plug a lamp cord into electrical outlet. A port is one of the entry lines coming into the computer. A port provides a direct link to the microcomputer’s common electrical bus.
Types of Computer Ports
There are two types of ports used in computer:
Serial Ports Parallel Ports
A serial port provides a connection for transmitting data one bit at a time. A serial port connects your computer to a device such as modem, which requires two-way data transmission, or to a device such as a mouse, which requires only one-way data transmission. IBM-compatible computers use either 9-pin or 25-pin connectors for their serial ports COM1, COM2 etc.
A parallel port provides a connection for transmitting data eight bits at a time over a cable with eight separate dta lines. Parallel transmission is fast because eight bits travel simultaneously. Parallel transmission is typically used to send data to the printer. The cable that connects two parallel ports contains 25 wires, eight wires carry data and the remaining wires carry control signals that help to maintain orderly transmission and reception. IBM-compatible computes generally allow you to use up to three ports which are designated as LPT1, LPT2 etc.