BASIC ARCHITECTURE OF COMPUTER SYSTEMCHAPTER - II

• Basic Organization of a Computer System is called Computer Architecture.

• Different computer have different architecture. • But, basic organization remains the same for all

computer systems.• E.g. CPU, MEMORY, INPUT/OUTPUT Devices• Motherboard: In personal computers, a motherboard is the

central printed circuit board (PCB) and in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals (input/output devices).

Hardware Devices Analogy: A Paper-Based Office

Principles of Information Systems, Eighth Edition 2

Secondary Storage

Register Storage

Output

Primary Storage

Input

Logically there is no difference between a Computer and a Human

Principles of Information Systems, Eighth Edition3

A Computer Hardware System

Figure 3.1: Hardware Components

Chapter 2 content

• Basic organization of computer• What is motherboard• What is cpu• Components of CPU ( ALU, CU, MU<cache>)• Primary Storage (RAM)• Secondary Storage (Hard Disk, CD , Fash drive)• What is ROM• What is Computer Bus ( Data Bus, Control Bus, Address

Bus)• Input Devices and Ouput Devices

COMPUTER BLOCK DIAGRAM

Microprocessor /Processor/ CPU• The Central Processing Unit (CPU) carries out all the computer program

instructions. • Choosing the right CPU has a great impact on performance.• Two very popular choices of CPU for use in a PC are:• The Pentium series from Intel • The Athlon series from AMD

Multiple CPUs

• Another way of boosting performance is to use more than one CPU in the computer.

• This is called 'parallel processing'. Basically a computer program that has been especially written to work in this way will split up its tasks so that both CPUs work at the same time.

Multicore CPU

• A multi-core processor is a single computing component with two or more independent actual processors (called "cores"), which are the units that read and execute program instructions.

• A dual-core processor has two cores (e.g. AMD Phenom II X2, Intel Core Duo), a quad-core processor contains four cores (e.g. AMD Phenom II X4, the Intel 2010 core line that includes three levels of quad-core processors, see i3, i5, and i7 at Intel Core), a hexa-core processor contains six cores Intel Core i7 Extreme Edition 980X), an octa-core processor contains eight cores (e.g. AMD FX-8150).

CPU…. Continue

• CPU stands for central processing Unit.• Each CPU has a set of pins through which all

its communication takes place with the other devices.

• CPU consists of two units – ALU (Arithmetic and Logic Unit)– CU (Control Unit)

• CPU located on motherboard.

1. Arithmetic and Logic Unit (ALU)

• All arithmetic and logical operations are performed in ALU.

• Asthmatic Operations such as– (+, *, -, %, /)

• Logical Operations such as – (>, <, >=, <=, !=, =, ==)

• No processing occurs in primary storage.• Data move from primary storage to ALU or vice

versa.

Control Unit (CU)• Act as a supervisor of the computer.• The control unit is the circuitry that controls the flow of

information through the processor, and coordinates the activities of the other units within it.

• In a way, it is the "brain within the brain", as it controls what happens inside the processor, which in turn controls the rest of the PC.

• The control unit is one of the most important parts of a microprocessor for the reason that it is in charge of the entire process, that is the machine cycle. The CPU deals with each instruction it is given in a series of steps. Each step is repeated for each instruction.

Control Unit (CU)

• This series of steps is called the machine cycle (fetch-decode-execute cycle). It involves:

• fetching an instruction from memory;• decoding the instruction;• transferring the data;• executing the instruction.

The control unit makes sure that all of those actions are carried out. It also manages all the other components on the CPU.

Memory Unit (MU)• CPU has its own memory to store data. (Cache) • Like L1, L2, L3 (A shared Memory ) • Instructions are also stored in this memory/CPU registers.• These are the fastest storage area in a computer.

MU vs Mail Box Example• The location in memory for each instruction and each piece of data

is identified by an address. • That is, each location has an address number, like the mailboxes in

front of an apartment house. And, like the mailboxes, the address numbers of the locations remain the same, but the contents (instructions and data) of the locations may change. That is, new instructions or new data may be placed in the locations when the old contents no longer need to be stored in memory.

MEMORY• In computing, memory refers to the physical devices used to store

programs (sequences of instructions) or data (e.g. program state information) on a temporary or permanent basis for use in a computer or other digital electronic device.

• A typical computer contains numerous types of memory including – RAM (Random Access Memory)– ROM (Read Only Memory)– Virtual Memory

RAM• RAM is the most common type of memory found in computers and other devices,

such as printers.• There are two different types of RAM: DRAM (Dynamic Random Access Memory)

and SRAM (Static Random Access Memory).• The two types differ in the technology they use to hold data, with DRAM being

the more common type. In terms of speed, SRAM is faster. DRAM needs to be refreshed thousands of times per second while SRAM does not need to be refreshed, which is what makes it faster than DRAM. DRAM supports access times of about 60 nanoseconds, SRAM can give access times as low as 10 nanoseconds.

• Despite SRAM being faster, it's not as commonly used as DRAM because it's so much more expensive.

• Both types of RAM are volatile, meaning that they lose their contents when the power is turned off.

• In common usage, the term RAM is synonymous with main memory, the memory available to programs.

ROM

• ROM (read-only memory) refers to special memory used to store programs that boot the computer and perform diagnostics. Most personal computers have a small amount of ROM (a few thousand bytes). In fact, both types of memory (ROM and RAM) allow random access. To be precise, therefore, RAM should be referred to as read/write RAM and ROM as read-only RAM.

Read Only Memory (ROM) Types

There are five basic ROM types:1. ROM - Read Only Memory2. PROM - Programmable Read Only Memory3. EPROM - Erasable Programmable Read Only

Memory4. EEPROM - Electrically Erasable Programmable

Read Only Memory

Each type has unique characteristics, but all types of ROM memory have two things in common:

• Data stored in these chips is non-volatile -- it is not lost when power is removed.

• Data stored in these chips is either unchangeable or requires a special operation to change.

PROM

• Data are written into a ROM at the time of manufacture. However a PROM , allows the data to be loaded by the user. Creating ROM chips totally from scratch is time-consuming and very expensive in small quantities. For this reason, developers created a type of ROM known as programmable read-only memory (PROM). Blank PROM chips can be bought inexpensively and coded by the user with a programmer. PROMs provide a faster and less expensive approach for storing.

EPROM

Working with ROMs and PROMs can be a wasteful business. Even though they are inexpensive per chip, the cost can add up over time. Erasable programmable read-only memory (EPROM) addresses this issue. EPROM chips can be rewritten many times. Erasing an EPROM requires a special tool that emits a certain frequency of ultraviolet (UV) light. EPROMs are configured using an EPROM programmer that provides voltage at specified levels depending on the type of EPROM used.

• An EPROM eraser is not selective, it will erase the entire EPROM. The EPROM must be removed from the device it is in and placed under the UV light of the EPROM eraser for several minutes. An EPROM that is left under too long can become over-erased. In such a case, the EPROM's floating gates are charged to the point that they are unable to hold the electrons at all.

EEPROMs

• Though EPROMs are a big step up from PROMs in terms of reusability, they still require dedicated equipment and a labour-intensive process to remove and reinstall them each time a change is necessary. Also, changes cannot be made incrementally to an EPROM; the whole chip must be erased. Electrically erasable programmable read-only memory (EEPROM) chips remove the biggest drawbacks of EPROMs.

• In EEPROMs:• The chip does not have to removed to be

rewritten.• The entire chip does not have to be

completely erased to change a specific portion of it.

• Changing the contents does not require additional dedicated equipment.

Virtual Memory

• The term primary memory is used for the information in physical systems which are fast (i.e. RAM), as a distinction from secondary memory (Hard Disk, Compact Disk etc.), which are physical devices for program and data storage which are slow to access but offer higher memory capacity. Primary memory stored on secondary memory is called "virtual memory".

Computer/System Bus

.• A collection of wires which data is transmitted from oe part of a

computer to another. • Think, Bus as a highway• The size of a bus, known as its width , for example 16-bit bus• Internal Bus

Computer Bus …… Continue

• Data needs to move around the computer, for example:• The CPU needs to move information in and out of memory• Data needs to move between the hard disk and the CPU.• Data needs to move between the graphics card and the CPU• Data needs to move between the CDROM / DVD and the CPU • The way that data is moved from one place to another is

via a 'bus'. • A 'bus' is a set of wires or copper tracks that are built into

the motherboard.

• A bus usually contains between 1 to 64 wires (or more), the number of wires equals the number of 'bits' that can be transferred in one clock cycle.

• An 8 bit bus has 8 wires - it can transfer 8 bits in one go, with 1 bit on each wire.

• A 16 bit bus can transfer 16 bits in one cycle - 1 bit per wire.

• Current PCs have 32 bit buses and the newer generation are going to use 64 bit wide buses.

Types of Computer Bus

• Data Bus– Used to carry data signals– E.g numbers which we want to add or the string which we want to compare. – Transfer data from main memory (Ram) to CPU and vice versa or other part

of computer.

• Address Bus– Used to carry address signals – E.g address of memory location or a port(interface – where an input or

output device is attached.

• Control Bus– It used to carry control signals– E.g read/write , enable / disable etc.