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COMPUTER: 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 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
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).
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 auxiliary storage or 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
Some Examples of secondary storage devices are as follows:
1.
Magnetic Disks
2. Magnetic Tape
3.
Mass Cartridge Systems
Types of Secondary Storage/Backing Storage Access Methods
There are two 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
to search 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
There are two main buses in a computer:
1. Data Bus
2. Address Bus
Data 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.
Address Bus
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.
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 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:
1. Serial Ports
2. Parallel Ports
Serial 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.
Parallel Ports
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.
Memory Unit
Memory unit is the place where the computer program and data are
stored during processing. It is the area, through which all the
data which is input into or output of the CPU must pass. It is monitored
by OU which keeps track of every thing in the storage. It is a random
access device, which consists of thousands upon thousands of storage
locations, each of which can be directly reached by the CU. Each
storage location is distinguished by the address.
Types of Memory Unit
It is divided into two parts:
1. Read Only Memory (ROM)
2. Random Access Memory (RAM)
Read Only Memory (ROM)
This part of memory contains permanently stored information. When
the power is switched off. ROM does not wash away. This information
is available to a computer to read and process but not to be changed
is kept on ROM. This information is stored on small pieces of memory
chips, before the computer is assembled.
Random Access Memory (RAM)
This part of memory consists of blank chips and hence the computer
can use it to store and retrieve (write and read) information during
its processing. The information stored in RAM is volatile, that
is, when the computer is shut down the stored information is lost. |
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