Computer Components

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 used on a tiny silicon chip. This chip contains millions of switches and path ways that help your computer make important decisions.The switches control the flow of the electricity as it travels acrossthe 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

Control Unit (CU)

The Control Unit (CU) is the circuitry that controls the flow of information through the processor, and coordinates the activities of the other units within the processor. It is the "brain within the brain", as it controls what happens inside the processor, which in turn controls the rest of the PC.

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 ofoperations: 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. 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).

Secondary Storage

Secondary storage or secondary memory also referred as backing storage is used to supplement the capacity of main storage; the memory stores a bulk of information. It is also called mass storage. The information stored in this memory is used by the CPU by first bringing it to main memory.

Examples of Secondary Storage Devices

1. Magnetic Disks

2. Magnetic Tape

3. Mass Cartridge Systems

Types of Secondary Storage/Backing Storage Access Methods

Sequential Access Storage

Access through sequential access storage is non-addressable that is why an operator cannot refer directly to the contents of a particular storage location such as used with magnetic tape. This involves examining sequentially all beginning of the tape and continuing tosearch through all record until the desired information area is found.

Direct Access Storage

Direct Access Storage is addressable that is a given item can be selected from anywhere in storage by simply specifying the address where it is located direct access devices such as magnetic disks provide immediate access to individual records and do not require reading from the beginning of a file to find a particular record.

Computer Bus

In computer the term bus refers that paths between the components, actually bus, is a group of a wire. The bus is the common path way through which the processors send/receive data and commands to/from primary and secondary storage and all can transport 8 bits at a time whereas a bus with 16 lines can transport 16 bits at a time.

Types of Computer Bus

The address bus (sometimes called the memory bus) transports memory addresses which the processor wants to access in order to read or write data. It is a unidirectional bus.

The data bus transfers instructions coming from or going to the processor. It is a bidirectional bus.

The control bus (or command bus) transports orders and synchonisation signals coming from the control unit and travelling to all other hardware components. It is a bidirectional bus, as it also transmits response signals from the hardware.

Computer Ports

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 asa keyboard, mouse, monitor and a printer come with a cable and 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 lampcord into electrical outlet. A port is one of the entry lines coming into the computer. A port provides a direct link to the microcomputer'scommon electrical bus.

Types of Computer Ports

There are two types of ports used in computer:

1. Serial Ports

2. Parallel Ports

Serial Ports

A serial port provides a connection for transmitting data one bit ata 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 amouse, 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.

Parallel Ports

A parallel port provides a connection for transmitting data eight bits at a time over a cable with eight separate data 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 asLPT1, LPT2 etc.