Computer Components
(Chapter - 5)
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:
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).
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
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.
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.
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
1. Data Bus
2. Address Bus
1. 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.
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.
2. 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.
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
1. Serial Ports
2. Parallel Ports
1. 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.
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.
2. 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.
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)
1. Read Only Memory (ROM)
2. Random Access Memory (RAM)
1. 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.
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.
2. 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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