Module 3 Introduction To Computer System : Structure & Processes Introduction To Computer System : Structure & Processes

Module Objectives At the end of the module, students should be able to: –understand the concept and functions of a computer system –identify the component of a computer –identify the components of the central processing unit and explain how they work together and interact with memory –describe how program instructions are executed by the computer –explain how data is represented in the computer –understand the concept of bit and byte –identify the types of ports and connectors

What is A Computer System ? A functional unit, consisting of one or more computers and associated software, that uses common storage for the execution of the program. Consists of three components –People Computer programmer Users/End-user –Software –Hardware

Functions Of A Computer System

Components Of A Computer Systems Interconnection i.e. bus CPU Main Memory Input / Output Communication Lines Peripherals Computer

Complex set of electronic circuitry Executes stored program instructions Two parts –Control unit –Arithmetic/logic unit (ALU) Central Processing Unit Sends data to the CPU Registers Control Unit ALU Unit Processing Input Output Secondary storage Stores data and programs Makes processed info available Central Processing Unit

Control Unit Directs the computer system to execute stored program instructions Must communicate with memory and ALU Sends data and instructions from secondary storage to memory as needed

Arithmetic Logic Unit Executes all arithmetic and logical operations Arithmetic operations –Addition, subtraction, multiplication, division Logical operations –Compare numbers, letters, or special characters –Tests for one of three conditions Equal-to condition Less-than condition Greater-than condition

Intel Advanced Micro Devices (AMD) CyrixMotorola (Apple) Pentium IV Pentium MMX Pentium III Popular CPUs

shared communication link set of wires used to connect multiple subsystems A Bus is also a fundamental tool for composing large, complex systems The input/output bus provides a pathway so that the microprocessor can communicate with input/output devices Systems Interconnection (Bus) Control Data path Memory Processor Input Output

Input / Output Bus An input/output bus contains expansion slots which hold expansion cards –ISA (Industry Standard Architecture) slot  phased out –PCI (Peripheral Component Interconnect) slots –AGP (Accelerated Graphics Port) slot  usually for graphics card –USB (Universal Serial Bus) –PCI Express (PCI-E)  latest tech. PCI slots Expansion Card AGP slotsPCI-E slots

Data Storage and the CPU Two types of storage: –Primary storage (memory) Stores data temporarily / volatile CPU refers to it for both program instructions and data Holds input to be processed or holds results of processing –Secondary storage Long-term storage / non-volatile Stored on external medium, such as a disk

The CPU and Memory CPU cannot process data from disk or input device –It must first reside in memory –Control unit retrieves data from disk and moves it into memory Items sent to ALU for processing –Control unit sends items to ALU, then sends back to memory after processing Data and instructions held in memory until sent to an output or storage device or program is shut down

Temporary Storage Areas High-speed temporary storage areas –located within the CPU Work under direction of control unit –Accept, hold, and transfer instructions or data –Keep track of where the next instruction to be executed or needed data is stored Also known as primary storage / main memory –Often expressed as random- access memory (RAM) –Not part of the CPU Holds data and instructions for processing Stores information only as long as the program is in operation Memory Registers

The Machine Cycle The time required to retrieve, execute, and store an operation Components –Instruction timeInstruction time –Execution timeExecution time System clock synchronizes operations

The Machine Cycle Instruction Time = I-Time –Fetch – Gets the next program instruction from the computer’s memory –Decode – Figures out what the program is telling the computer to do Execution Time = E-Time –Execute – Performs the requested action –Write-back (Store) – Writes (stores) the results to a register or to memory

OFF ON 01 OR = 1 bit OR = 1 Byte OFF 00 How Computers Represent Data Bit (Binary digit) – On or off state of electric current; considered the basic unit of information; represented by 1s and 0s (binary numbers) Byte – Eight bits grouped together to represent a character (an alphabetical letter, a number, or a punctuation symbol); 256 different combinations ON

1000 bits = 1 kilobit (kb) 1,000,000 bits = 1 megabit (mb) 1,000,000,000 bits = 1 gigabit (gb) üKilobits per second (Kbps), Megabits per second (Mbps), and Gigabits per second (Gbps) are terms that describe units of data used in measuring data transfer rates –Example: 56 Kbps modem Bits

Bytes 8 bits = 1 Byte 1024 Bytes = 1 Kilobyte (KB) 1,048,576 Bytes = 1 Megabyte (MB) 1,043,741,824 Bytes = 1 Gigabyte (GB) 1,099,511,627,776 Bytes = 1 Terabyte (TB) Kilobyte, megabyte, gigabyte, and terabyte are terms that describe large units of data used in measuring data storage –Example: 20 GB hard drive Each byte has 256 (2 8 ) possible values

Kilobyte: 1024 (2 10 ) bytes –Memory capacity of older personal computers Megabyte: roughly one million (2 20 ) bytes –Personal computer memory –Portable storage devices (diskette, CD-ROM) Gigabyte: roughly one billion (2 30 ) bytes –Storage devices (hard drives) –Mainframe and network server memory Terabyte: roughly one trillion (2 40 ) bytes –Storage devices on very large systems Storage Sizes

Coding Schemes Provide a common way of representing a character of data Needed so computers can exchange data Common Schemes –ASCII –EBCDIC –Unicode

= 4 Representing Characters : Character Codes üCharacter codes translate numerical data into characters readable by humans –American Standard Code for Information Interchange (ASCII) – Eight bits equals one character; used by minicomputers and personal computers –Extended Binary Coded Decimal Interchange Code (EBCDIC) – Eight bits equals one character; used by mainframe computers –Unicode – Sixteen bits equals one character; over 65,000 combinations; used for foreign language symbols ASCII EBCDIC

Inside the System Unit / Casing üMotherboard (mainboard) – Large printed circuit board with thousands of electrical circuits üPower supply – Transforms alternating current (AC) from wall outlets to direct current (DC) needed by the computer üCooling fan – Keeps the system unit cool üInternal Speaker – Used for beeps when errors are encountered üDrive bays – Housing for the computer’s hard drive, floppy drive, and CD-ROM / DVD-ROM drives

Drive bays On/off switch Reset button Indicator lights FRONT BACK üThe front panel contains drive bays, various buttons, and indicator lights üConnectors and ports are physical receptacles located on the back to connect peripheral devices to the computer Outside the System Unit

Types of Connectors / Ports A 15 pin connector used for monitors For graphics-intensive interaction Data flows through eight wires allowing the transfer of eight bits of data simultaneously; faster than serial ports Allows up to 127 devices to be connected at a time. keyboard port - Special serial port to connect keyboard. Mouse port – Special serial port to connect mouse. Also called jacks, sound card connectors accept stereo mini- plugs. Microphone, line-in, line-out, and speaker connectors are plugged into the card. Serial port – Data flows in a series of pulses, one after another one bit at a time; slow data transfer rate.

Other Types of Connectors Small computer system interface (SCSI) port – A parallel interface that enables up to eight devices to be connected to it 1394 (FireWire) port – A high-speed connection for up to 63 devices Infrared Data Association (IrDa) port – Infrared signals are used to communicate between peripheral devices and the system unit