Computer Organization

Chapter # 5 Computer System Organization

CONTENTS • MOTHERBOARD • CPU – ALU – CU • MEMORY – RAM(SRAM,DRAM) – ROM(PROM,EPROM,EEPROM)

CONT… • REGISTERS • MICROPROCESSOR • VON NEUMAN ARCHITECTURE

Motherboard • Motherboard is also called system board. • Many electronic components are connected to the motherboard and some components are built into it.

• The processor chip and memory chip are plugged (installed) into the motherboard. • The motherboard contains sockets or slots in which electronic components are installed.

Central Processing Unit (CPU) • Central Processing Unit (CPU) is also called processor.

• It interprets and executes the instructions to run the computer system. • It is the brain of the computer system.

Cont…CPU –It perform all operations on the data according to the instructions. –It carriers out instructions and tells other parts of computer system what to do.

Cont…CPU –CPU consists of two main units. –Arithmetic and Logic Unit (ALU) –Control Unit (CU)

Arithmetic and Logic Unit(ALU) – ALU is a part of CPU. – Actual execution of the instructions takes place in this part. – All arithmetic and logical operations are performed in ALU.

Cont…ALU • It consists of two units. •Arithmetic Unit •Logic Unit

Arithmetic Unit Arithmetic Unit of the ALU performs basic functions such as: •Addition, •Subtraction, •Multiplication and •Division.

Logic Unit LU performs logical operations like comparing two data items to find which data item is:

•Greater than •Equal to •Not equal to or •Less than the other.

Control Unit (CU) • It is the most important component of the CPU. • It controls and coordinates the activities of all units of the computer.

Functions of CU • CU performs the following operations:

–It fetches instructions from the main memory. –It interpret that instruction to find what operation is to be performed. –It controls the execution of instruction.

Memory • Data and instructions are stored in memory to be executed. • This memory is temporary storage unit for data, instructions and information.

Cont.. • It is also called primary storage. • It consists of one or more chips on the motherboard.

Cont…Memory • Memory stores the following three items: –Operating system and other system software to control the computer system.

Cont…Memory –Application programs to perform specific tasks. –Data to be processed by the application programs

Cont…Memory • The instruction and data is stored in memory as bytes during execution. • Each byte in memory has its unique address that identifies its location.

Types Of Memory Memory is divided into two basic types: 1. RAM • SRAM • DRAM

2. ROM • PROM • EPROM • EEPROM

Random Access Memory • RAM stands for Random Access (RAM) Memory.

• Main memory is referred to as RAM. • It is a volatile memory and the contents of the memory are lost as soon as the electricity supply is cut-off.

Cont…RAM • The CPU can write and read to and from the RAM. So RAM is also known as read/write memory. • It is used to store all data and instructions of a program while it is being executed.

Cont…RAM • RAM’s are built using two different technologies. Therefore, RAM is divided into two types. –DRAM –SRAM

DRAM • DRAM sands for Dynamic Random Access Memory. • This type of memory is used in most of the computers. • In order to maintain data in DRAM chip, it must be re-energized with electric charge frequency otherwise data stored in DRAM may be lost.

SRAM • SRAM stands for Static Random Access Memory. • It is more reliable. • In SRAM, chips are not re-energized as often as in DRAM so called as static.

Comparison between DRAM and • SRAM is faster than DRAM SRAM

because it does not have to be refreshed with electric charge frequently and CPU has not to wait to read and write data.

Cont… • SRAM utilizes less power. • The design of SRAM is more complex than the design of DRAM. • SRAM chip is more expansive than DRAM chip.

Read Only Memory • ROM stands for Read Only (ROM) Memory.

• The contents (i.e., instructions) stored in this memory can be read but new data cannot be written into it. Therefore it is called as read only memory.

Cont… ROM • The manufacture of the ROM writes the data and programs permanently into it and contents of this memory cannot be changed afterwards. • ROM is a non-volatile memory. So the data and programs stored in ROM chip is not lost when electricity is cut-off.

PROM • PROM stands for Programmable Read Only Memory. • It is a Blank ROM chip onto which a programmer can write Instructions. • Once the ROM chip has being written it functions like regular ROM and cannot be erased or changed.

EPROM • EPROM stands for Erasable Programmable Read Only Memory. • Like PROM, it is initially blank and the user or manufacture can writes his own program or data by using special devices.

Cont… • Unlike PROM, the data written in EPROM chip can be erased by using special purpose devices and ultraviolet rays. So program or data written in EPROM chip can be changed and new data can also be added on this form of ROM. • When EPROM is in use, its contents can only be read.

EEPROM • EEPROM stands for Electrically Erasable Programmable Read Only Memory. • This kind of ROM can be rewritten by using electrical devices • Data stored on this ROM chip can be easily modified.

Cache memory • A cache (pronounced "cash") is a small and very fast memory. • It is designed to speed up the transfer of data and instructions. • It is faster than RAM. The data and instructions that are most recently or most frequently used by CPU are stored in cache.

Cont… • The data and instructions are retrieved from RAM when CPU uses them for first time. A copy of that data or instructions is stored in cache. When next time CPU needs that data or instructions, it first looks in cache. If the required data is found there, it is retrieved from cache memory instead of main memory. It speeds up the working of CPU.

Flash Memory • Flash memory is also called flash ROM or flash RAM. • It is a type of nonvolatile memory. It can be erased electronically and reprogrammed.

Cont… • Most computers use Flash memory to hold their startup instructions. • Flash memory chip are used to store data on handheld computers like cellular phones, digital cameras etc.

Memory Access Time The amount of time required by processor to read data, instructions and information from memory is called access time.

Expansion Slots • Expansion slot is a socket that is mounted on a motherboard to insert circuit board. • Different circuit boards are inserted into the motherboard to add new devices and enhance capabilities to the computer.

Cont… • Some examples are memory chips, sound devices, modems or graphics card etc. Different types of expansion cards are as follows: Video Card - It is also called video adapter or graphics card. It converts computer output into a video signal and sends it to the monitor to display.

Sound Card – It enhances the sound-generating capabilities of a computer. It allows sound to be input through microphone and output through speakers. Network Interface Card (NIC) – It is also called network card. It is a communication device that allows a computer to communicate via a network.

Modem Card It is also called an internal modem. It is a communication device that enables computer to communicate via telephone line.

Ports • A port is an interface or point of attachment. • It is used to connect peripheral device with computer such as printers, keyboards or mouse.

Cont…Ports • Ports have different types of connectors. • A connector joins a cable to a device. One end of the cable is attached to connector on the system unit and the other end is attached to the connector on the peripheral device

Different Types of ports Different types of Ports are as follows: 1. Serial port 2. Parallel Port 3. USB Port

Serial port •

A serial port is used to connect devices to the system unit.

• A serial port transmits data one bit at a time through a single wire.

Parallel Ports • Parallel port is used to connect devices that transfer 8 bits at a time. • Printers connect to computer using a parallel port. • The transmission of data through parallel port is faster than serial port.

Universal Serial Bus • USB stands (USB) Port for Universal

Serial

Bus.

• Many computers have two to four USB ports either on the front or back of the system unit. • USB port also support hot plugging and plug and play. It means that you can attach devices with the computer while computer is running. You have not to restart the computer after attaching the

Power Supply • It is an electrical component inside the system unit that converts the AC power into the DC power. • It supplies the correct voltage or power to all parts of the computer. • It is a simple electrical system, which takes 240 or 110 voltages and convert them into DC voltage of 3V, 6V, 12V and 24V.

BUS • The electrical paths through which computer (CPU) send and receives data and instructions to and from different components of computer are called computer buses.

Cont… • A bus consists of 40 to 150 electric wires or lines running parallel to each other. One line can carry one bit at a time. The amount of data that a bus can carry is called “bus width”. • The capacity of computer bus depends on the data lines it contains. For example a bus with 16 lines can transfer 16 bit at a time.

Registers • •

• •

Registers are the specialpurpose, high-speed memories inside the CPU. The size of the register is the number of bits it can hold at a time. The register that can store 8 bits is referred to as 8-bit register. Usually a register can hold 8,16,24 and 32 bits of data. The larger the size of register, the greater will be the data processing speed of the CPU.

Cont… • Registers are used for special purpose: •Temporary storage of memory addresses •Temporary storage of instructions during execution of the program. •Temporary storage of data being worked upon by the CPU.

Register S.No

Name of Register

FUNCTION

1.

Memory Address (MAR)

Hold address of active memory location

2.

Memory Buffer (MBR)

Hold information on its way to and from memory

3.

Program control (PC)

Hold address of the next instruction to be executed

4.

Accumulator (A) Accumulates results and data to be operated upon

5.

Instruction Register (IR)

Hold instruction, while it is being executed

6.

Input/output (I/O)

Communicates with I/O devices

Microprocessor • Today, microprocessor used in microcomputers designed in a single chip and fits into special socket on the motherboard.

Microprocessor • In personal computers, two types of microprocessors are used. 1. Intel Microprocessor 2. Motorola Microprocessor

Intel Microprocessor • This microprocessor made by Intel Corporation. • It is used in microprocessor. • 90% microcomputers used this type of microprocessor. • Microsoft Windows Operating System is developed to run on Intel microprocessor. • Most advanced microprocessor chip of Intel is P4.

Motorola Microprocessor: • It is made by Motorola. • It is used in personal computers of Apple. • Macintosh OS is developed to run on Motorola microprocessor.

VON NEUMAN ARCHITECTURE: A computer’s program can be changed by changing the contents of memory instead of rewiring CU. This STORED PROGRAM CONCEPT has the standard approach used today.

Cont.. To apply it , a machine is designed to recognized certain bit pattern as representing certain instructions. this is called machine language

Machine Language • Machine language defines the mean by which we communicate algorithms to machine. • The coded version of a machine instruction typically consist of two parts: – Op-code field – Operand field

Op-code field • Op- code field indicates which of the elementary operation is requested by the instruction. • Elementary operation are STORE , SHIFT, XOR , and JUMP.

Operand field • Bit pattern found in operand field provide more detail information about operation specified by op-code field. • E.g. – In case of STORE operation , the information in the operand field indicates which register contain data to be stored and which memory cell is to receive the data.

Program Execution • Machine cycle provide an algorithm to CU to perform its job continuously, • Cycle consist of – FETCH – DECODE – EXECUTE

Fetch • CU request that main memory provide it with the next instruction to be executed. • The unit knows where the next instruction is in memory because its address is kept in program counter. • CU place the instruction received from memory in its instruction register • Then increment the program counter, so it get address of next instruction.

Decode: • With the instruction in IR,CU decode the instruction , which involves the breaking instruction into op-code and operand.

EXECUTE: • CU then execute the instruction by activating the appropriate circuitry to perform requested task.

Example of program ADDRESS CONTENTS execution A0 A1 A2 A3 A4 A5 A6 A7 A8

15 6C 16 6D 50 56 30 6E C0

A9

00

Example of program Step 1: CU begins the fetch step by execution

extracting the instruction at location A0 and placing the instruction in IR. – Note that in our machine instruction are 16 bits long. – So instruction to be fetched occupies the memory cell at both address A0 and A1. – CU are design in manner that it can receive contents from both cells and place it in IR , which is 16-bit long

Example of program CU adds 2 in the PC, so it gets address execution of next instruction Now PC : A2 IR : 156C

• Step 2: CU analyze instruction in IR and conclude ,

• Step 3: LOAD register 5 with the contents of memory cell at 6C. CU then begins the next cycle.