COMPUTER ARCHITECTURE

Computer architecture deals with the functional behaviour of a computer system as viewed by a programmer. It can also be described as the logical structure of the system unit that housed electronic components. The computer architecture forms the backbone for building successful computer systems.

The first computer architecture was introduced in 1970.

 

Components Of Computer

A computer consists of following three main components

1.  Input/Output (I/O) Unit

2. Central Processing Unit

3. Memory Unit

Note System unit is a metal or plastic case that holds all the physical parts of the computer. The components that process data are located in it.

 

Input Unit

The computer accepts coded information through input unit by the user. It is a device that is used to give required information to the computer. e.g. Keyboard, mouse, etc.

An input unit performs the following functions

1.     It accepts the instructions and data from the user.

2.     It converts these instructions and data in computer in acceptable format.

3.     It supplies the converted instructions and data to the computer system for further processing.

 

Output Unit

This unit sends the processed results to the user. It is mainly used to display the desired result to the user as per input instruction. e.g. Monitor, printer, plotter, etc.

The following functions are performed by an output unit

1.     It accepts the results produced by the computer which are in coded form and hence cannot be easily understood by user.

2.     It converts these coded results to human acceptable form.

3.     It supplies the converted results to the user.

 

Central Processing Unit (CPU)

It consists a set of registers, arithmetic logic unit and control unit, which together interpret and execute instructions in assembly language.

The primary functions of the CPU are as follows

1.     The CPU transfers instructions and input data from main memory to registers, i.e. internal memory.

2.     The CPU executes the instructions in the stored sequence.

3.     When necessary, CPU transfers output data from registers to main memory. Central Processing Unit is often called the brain of computer. The CPU is fabricated as a single Integrated Circuit (IC) and is also known as microprocessor.

A CPU controls all the internal and external devices and performs arithmetic and logic operations.

 

The CPU consists of following main sub-systems

Arithmetic Logic Unit (ALU)

ALU contains the electronic circuitry that executes all arithmetic and logical operations on the available data. ALU uses registers to hold the data that is being processed.

Most ALUs can perform the following operations

1.     Logical operations (AND, NOT, OR, XOR).

2.     Arithmetic operations (addition, subtraction, multiplication and division).

3.     Bit-shifting operations (shifting or rotating a word by a specified number of bit to the left or right with or without sign extension).

4.     Comparison operations (=, <, < =, >, > =)

 

Registers

These are used to quickly accept, store and transfer data and instructions that are being used immediately by the CPU. These registers are the top of the memory hierarchy and are the fastest way for the system to manipulate data. The number and size of registers vary from processor to processor.

 

Control Unit (CU)

CU coordinates with the input and output devices of a computer. It directs the computer to carry out stored program instructions by communicating with the ALU and the registers. It organises the processing of data and instructions.

The basic function of control unit is to fetch the instruction stored in the main memory, identify the operations and the devices involved in it and accordingly generate control signals.

 

Microprocessor

It is the controlling element in a computer system and is sometimes referred to as the chip. Microprocessor is the main hardware that drives the computer. It is a large Printed Circuit Board (PCB), which is used in all electronic systems such as computer, calculator, digital system, etc. The speed of CPU depends upon the type of microprocessor used.

1.     Intel 4004 was the first microprocessor made by Intel in 1971 by scientist Ted Hoff and engineer Frederico Faggin.

2.     Some of the popular microprocessors are Intel, Intel core i7, Dual core, Pentium IV, etc.

 

Memory Unit

This unit is responsible to store programs or data on a temporary or permanent basis. It has primary memory (main memory) and secondary memory (auxiliary memory).

The input data which is to be processed is brought into main memory before processing.

Another kind of memory is referred to as secondary memory of a computer system. This unit is used to permanently store data, programs and output. This unit does not deal directly with CPU.

 

Motherboard

The main circuit board contained in any computer is called a motherboard. It is also known as the main board or logic board or system board or planar board. All the other electronic devices and circuits of computer system are attached to this board like, CPU, ROM , RAM, expansion slots, PCI slots and USB ports. It also includes controllers for devices like the hard drive, DVD drive, keyboard and mouse. In other words, motherboard makes everything in a computer work together.

 

Components on Motherboard

Various components on motherboard are as follows

1.    CMOS Battery

2.    BIOS Chip

3.    Fan

4.    Expansion Slot

5.    SMPS

6.    PCI Slot

7.    Processor Chip

8.    Buses

 

Interconnection Of Units

CPU sends data, instructions and information to the components inside the computer as well as to the peripheral devices attached to it.

A bus is a set of wires used for interconnection, where each wire can carry one bit of data.

In other words, bus is a set of electronic signal pathways that allows information and signals to travel between components inside or outside of a computer.

 

A computer bus can be divided into two types

1.    Internal Bus The internal bus connects components inside the motherboard like CPU and system memory. It is also called the system bus.

Internal bus includes following buses

a)    The command to access the memory or the I/O devices is carried by the control bus.

b)    The address of I/O devices or memory is carried by the address bus. The data to be transferred is carried by the data bus.

2.     External Bus It connects the different external devices; peripherals, expansion slots, I/O ports and drive connections to the rest of computer. It is also referred to as the expansion bus.

 

Tit-Bits

UPS (Uninterruptible Power Supply), is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails.

Buffer is a temporary storage where register holds the data for further execution.

Accumulator is a register in a CPU in which intermediate arithmetic and logic results are stored.

An uniform interval of CPU time allocated for use in performing a task is known as time slice.

The speed of processor is measured in millions of cycles per second or megahertz (MHz) by clock speed.

DMA (Direct Memory Access) is a method that allows an input/output device to send or receive data directly to or from the main memory, by passing the CPU to speed up memory operations.