COMPUTER SYSTEM ARCHITECTURE By Sohaib. The digital computer is a digital system that performs various computational tasks. The word digital implies.

COMPUTER SYSTEM

ARCHITECTURE

By Sohaib

The digital computer is a digital system that performs various computational tasks.

The word digital implies that the information in the computer is represented by variables that take a limited number of discrete values.

Digital computers use the binary number system, which has two digits, 0 and 1.

A binary digit is called a bit. Information represented in digital computers in groups of bits.

Binary number system use a base 2 system with two digits: 0 and 1.

The decimal equivalent of a binary number system can be found by expanding it into power series with a base of 2.

Example of binary number system is 1 0 1 1 0 . 1 124 23 22 21 20 2-1 2-2

To convert a binary number into its equivalent decimal number, multiply each digit times the decimal value of the digit and just add these up.

The binary number 101, represents(1 * 22) + (0 * 21) + (1 * 20)4 + 0 + 1 = 5 ( Decimal)

What is the decimal equivalent for 10110.11 ?

22710 = ?

10910 = ?

Conversion from decimal to binary is a simple method and is a part of a class exercise.

Computer require binary digits, so why use hexadecimal?

Example shows the digit values for hexadecimal which is often called hex.162 161 160 . 16-1 16-2

256 16 1 1/16 1/256

Dec Hex Dec Hex

0 = 0 8 = 81 = 1 9 = 92 = 2 10 = A3 = 3 11 = B4 = 4 12 = C5 = 5 13 = D6 = 6 14 = E7 = 7 15 = F

A computer system is sometimes subdivided into two functional entities i.e. Hardware and software.

The hardware of a computer is divided into three major parts. The central processing unit or Microprocessor. Memory (RAM). Interface, input output devices.

Logic Gates are circuits made up of transistors, diodes, and resistors. Logic gates process one or more input signals in a logical fashion. Depending on the input value or voltage, the logic gate will either output a value of '1' for ON or a value of '0' for OFF.

Logic Gates allow simplification of circuit operation. A basic understanding of logic gates will aid technicians in electrical diagnosis.

The five common logic gates used in wiring diagrams are the:AND, OR, NOT, NAND, NOR

Logic Gates are digital circuits. All digital circuits are either ON or OFF.

A light switch in your house can be used as an example of a digital circuit. The light is either ON or OFF depending on the switch position.

When the Light is ON the output value is '1'. When the Light is OFF the output value is '0'. The inputs are the position of the light switch.

The switch is placed either in the ON or OFF position to activate the Light.

One of the primary requirements when dealing with digital circuits is to find ways to make them as simple as possible.

One tool to reduce logical expressions is the mathematics of logical expressions, introduced by George Boole in 1854 and known today as Boolean Algebra. The rules of Boolean Algebra are simple and straight-forward, and can be applied to any logical expression. The resulting reduced expression can then be readily tested with a Truth Table, to verify that the reduction was valid.

Types of Computers

Mainframes Minicomputers Microcomputers

Mainframes:

The largest and most powerful computers are called Mainframes.

They are designed to work at a very high speeds with large data words, typically 64 bits or greater.

Examples are IBM 4381, Honeywell DPS8, Cray Y-MP/832

Minicomputers:

Scaled down version of mainframe computers are often called minicomputers.

A minicomputer runs slowly, works directly with smaller data words.

Computers of this type are used for business data processing, industrial control and scientific research.

Examples are DEC VAX-6360, Data General MV/8000II

Microcomputers: They are the small computers.

There are wide range of microcomputers depending on their specification.

Some microcomputers have all or most of the features of earlier minicomputers.

Microcomputer consist of a CPU ( usually a single integrated circuit) called a microprocessor.

Examples are Intel 80-51 single-chip controller, SDK-86, IBM PC, Apple Macintosh.

What is a Micro-processor?

A Microprocessor is used as a CPU in a microcomputer.

A semiconductor chip or chip set that forms the CPU

Controls computers input/output devices Executes programs

Microprocessor unit (MPU) Consists of an arithmetic logic unit (ALU),

a control unit, an instruction decoder and some registers.

The MPU Works by sequentially decoding instructions and operating on data under control of a program.

The instructions and the data are stored in memory.

A Microprocessor only is a single-chip CPU bus is available RAM capacity, num of port is selectable Communicate by port

A Microcomputer contains a CPU and RAM,ROM ,Peripherals, I/O port in a

single IC internal hardware is fixed Communicate by port ROM is larger than RAM (usually) Small power consumption Single chip, small board Implementation is easy Low cost

Applications

Microcomputers are suitable to control I/O devices in designs requiring a minimum component

Microprocessors are suitable for processing information in computer systems.

Microcomputer is easy to use and design. Only single chip can be a complete system interfacing to other devices, for example,

motors, displays, sensors, and communicate with PC.

In contrast, similar system that builds from Microprocessor would require a lot of additional units, such as RAM, UART, I/O , TIMER and etc.

Logic circuit provides limited function for one single design. In order to change circuit’s functionality, we need to redesign the circuits.

Microcomputers can reprogram and change functionality of every port, input to output or digital to analog on the fly.

All Microcomputers consist of (at least) : Microprocessor Unit (MPU) Program Memory (ROM) Data Memory (RAM) Input / Output ports Bus System (and Software)

MPU is the brain of microcomputer

Many microcomputers are existing right now. 8051, 68HC11, MSP430, ARM series, and etc.

We may widely divide it with how it is designed RISC/CISC architecture.

What is the main difference between RISC/CISC? Does it make any difference to our

application?