Computer Unit (1) (PPT)

The Computer System

What is a Computer?

A computer is an electronic device, operating under the control of instructions stored in its own memory unit, that can accept data (input), process data arithmetically and logically, produce results (output), and store the results for future use.

Components of a computer

Basic Components– Input Devices– System Unit– Output Devices– Storage Devices

Other Components– Peripheral Devices– Communication Devices

Strengths of Computers

Speed Reliability Accuracy Storage Communication/Connectivity

Types of Computer

Microcomputer (PC) Workstation Minicomputer Mainframe Computer Supercomputer

Increasing speed & processing power!

Data Representation

Bits– off or on digital value, short term for binary

digits. Bytes

– a group of eight bits, a unique code can be assigned to 256 different data possibilities. (e.g. 01000001 represents the letter A.)

Coding Scheme

ASCII (American Standard Code for Information Interchange)– 8 bits; used in many PC & minicomputer.

EBCDIC (Extended Binary Coded Decimal Interchange Code)– 8 bits; used in Mainframe Computer

Character ASCII EBCDIC Character ASCII EBCDICA 01000001 11000001 0 00110000 11110000B 01000010 11000010 1 00110001 11110001C 01000011 11000011 2 00110010 11110010D 01000100 11000100 3 00110011 11110011… …

Unicode– 16 bits – can represent > 65000 characters

1. System Unit

Components of System Unit

Motherboard Central Processing Unit (CPU) Memory Upgrade sockets Co-processor Buses Expansion Slot Ports & connectors

The Central Processing Unit

It is the brain of a computer system The CPU:

– receives input.– interprets instructions provided by programs.– directs other components of the system to act.– processes data.– controls output.

Control Unit

ALU

Registers

Memory

Bus

CPU

The Central Processing Unit

Control Unit– It coordinates the flow of data and instructions. It

contains a clock that generates a uniform stream of electrical pulses that synchronize the operating of the CPU and other computer components

Note: The control unit controls the computer by repeating 4 operations, called the machine cycle. The 4 operations are: fetching program instructions from memory; decoding the instructions into commands that the computer can process; executing the commands; and storing the results in memory

Note: The control unit controls the computer by repeating 4 operations, called the machine cycle. The 4 operations are: fetching program instructions from memory; decoding the instructions into commands that the computer can process; executing the commands; and storing the results in memory

Control Unit

ALU

Registers

Memory

Bus

CPU

The Central Processing Unit

Arithmetic and Logic Unit (ALU)– It performs calculations and comparisons

of data.

Registers– They hold program instructions, data

values, and memory locations as the computer executes a program.

Control Unit

ALU

Registers

Memory

Bus

CPU

The Central Processing Unit

BusesThey are electrical pathways that carry signal (bits) between a CPU’s components and outside devices.

The Central Processing Unit

Control Unit

ALU

Registers

Memory

Bus

CPU

Multiprocessing

Large computer systems, as well as newer workstations and network servers, frequently contain more than one central processing unit.

Multiple CPUs enable the computer to execute more than one instruction or process more than one program, at the same time.

Main Memory

Before programs are executed or data processed, they must first enter into main memory.

Main memory holds information read from disk or captured by input devices.

The CPU then moves information from the main memory into its registers for processing.

RAMROM CACHE

Random Access Memory (RAM)

Integrated circuit containing data that can be read and written by the microprocessor or other devices.

Volatile - programs & data stored in RAM are erased when the power is off.

Chips that store information or instructions that can be read and used, but cannot be changed.

Non-volatile - retains its contents even the power is turned off.

The instructions to start the computer are on a special chip known as a ROM BIOS chip (Basic Input/Output System).

Read Only Memory (ROM)

Cache Memory

Cache memory is a specialized chip used with the computer's memory.

Cache chips are faster and more expensive than regular RAM chips.

The computer stores the most frequently used instructions and data in cache. Cache has a relatively small storage capacity but can significantly increase the system's speed.

In summary, memory

accepts and holds program instruction and data

acts as the CPU’s source for data and instructions and as a destination for operation results

holds the final processed information until it can be sent to the desired output or storage devices, such as printer or disk drive

Motherboard A circuit board that contains most of the

electronic components of the system unit.

CPU Slot (PII)

DIMM Sockets for Memory

BIOS Chip

Ports & Connectors

Expansion Slots (for display card, modem card…)

Internet References

How microprocessor works (http://www.intel.com/education/mpuworks/index.htm)Introduction to PC (http://www.pcguide.com/intro/index.htm)Computer Hardware (http://www.ied.edu.hk/has/comp/component/index.htm)Tom’s Hardware Guide (http://www.tomshareware.com/guides/cpu.html)

Multimedia Tutorials (Available in SLCSS Intranet Only)

Lab 1: Computer FundamentalsLab 2: Central Processing Unit

2. Input Devices

Input Devices

Input devices, such as keyboards or scanners, are hardware components that capture, collect, and transmit data and programs to the computer in a form that computer can understand.

Input devices transmit the input to the computer in a series of electronic pulses representing bits, or digits, of the binary code.

Types of Input

Data– raw facts that a computer receives and processes to produce

information Programs

– instructions that direct the computer operations Commands

– key words that direct the computer to perform certain activities

User Responses– data a user enters to respond to a question or message.

A. Keyboard

The most commonly used input devices. Contains alphanumeric, cursors and

function keys.

Function key

Numeric keypad

• Function Keys, labeled from F1 to F12, allow user to quickly access commands and functions, such as saving a document or calling up a program’s Help feature.

• Cursor-control Keys govern the movement of the cursor on the screen. They include Up Arrow, Down Arrow, Left Arrow and Right Arrow key on the keyboard.

• Special Purpose Keys are used in conjunction with other keys to enter commands into a computer. Control (Ctrl), Alternate (Alt) and Shift keys are example of special purpose keys.

• Toggle Keys are keys that, when pressed, activates a certain mode or condition, and when pressed again, deactivates the condition. The Num Lock key, Cap Lock key and the Scroll Lock key are examples of toggle keys. (For example, pressing the Cap Lock key will cause all the alphanumeric characters to appear in capitals without holding down the Shift key.)

• Numeric Keypad, located in the far right portion of the keyboard, is used for entering numbers quickly and for performing the same operations as a calculator.

Not all keyboards have the same layout. Most keyboards have adopted the so-called QWERTY layout for the alphanumeric keys.

Not all keyboards have the same layout. Most keyboards have adopted the so-called QWERTY layout for the alphanumeric keys.

Types of Keyboard

104-key keyboardNatural keyboard

Keyboard for the Mac

B. Pointing Devices

Many people use pointing devices instead of keyboards whenever possible.

Pointing devices minimize the amount of typing (and the number of errors).

Mouse Palm-sized pointing devices a ball on the bottom senses its movement various actions can be preformed by moving the

pointer and then pressing one of the buttons on top of the mouse.

Types of Mouse

Cordless wheel mouse3-button mouse

Wheel mouse for notebooksiMouse for iMac

Mouse Interfaces

Serial

PS2

USB

Trackball

Up-side down mouse user rotates the ball itself while clicking

nearby buttons

TrackPoint Touchpad

The mouse is not practical for people using a notebook computer in a small space. Track Point or Touch pad is therefore used instead to control the pointer.

Touch-Sensitive Screens

Touch screens enable the user to select an option by pressing a specific part of the screen.

Touch screens are commonly used in grocery stores, fast-food restaurants, and information kiosks.

A touch screen kit solution

Joysticks

Use the movement of a vertical stem to direct the pointer.

C. Pen Input Devices

Input data with hand written characters, select items by pressing the pen against the screen, and use gestures, which are special symbols, to issue commands.

Light Pen

Used to select processing options or to draw on the screen

The tip of a light pen contains a highly sensitive photoelectric cell. When the light pen is pointed close to the screen, the photoelectric cell detects the light emitted from the exact spot the pen is touching. This accuracy makes light pens very popular among engineers and draftsmen who use computer-aided design (CAD) software to create blueprints and drawings of products or construction projects.

The tip of a light pen contains a highly sensitive photoelectric cell. When the light pen is pointed close to the screen, the photoelectric cell detects the light emitted from the exact spot the pen is touching. This accuracy makes light pens very popular among engineers and draftsmen who use computer-aided design (CAD) software to create blueprints and drawings of products or construction projects.

Digitizing Tablet A digitizing tablet consists of a grid on which

designs and drawings can be entered. Most tablets are pressure-sensitive, and the user

draws directly on the tablet using a special pen called a stylus.

Digitizing tablets are used to design cars, buildings, medical devices, and robots.

Chinese Handwriting Recognition Device Used for inputting and recognizing Chinese

handwriting

Nowadays, sophisticated Chinese handwriting recognition system also contains voice recognition function.

Nowadays, sophisticated Chinese handwriting recognition system also contains voice recognition function.

D. Scanning Devices

Image Scanner

Electronically capture an entire image & convert it into digital form that can be processed by a computer

Image Scan Edit

Bar Code Reader

Bar code consists of a set of vertical lines and spaces of different widths

Universal Product Code (UPC) is very common

An example of a bar code

Magnetic Ink Character Recognition (MICR) Use a special ink that can be magnetized during

processing MICR is used by the banking industry as a means

of processing checks it receives in every day.

Magnetic Ink Character

Optical Character Recognition

OCR software can be installed in a computer to perform character recognition.

a system of producing machine-readable code on a data source item and reading that code by means of optical scanning devices.

Optical Mark Recognition

Optical marks are the filled-in shape, usually ovals or rectangles, on scan sheets.

The data collected on the scan sheets are translated into binary form by an optical mark reader (OMR)

Use lead pencil to mark on scan sheet Feed the scan sheets into the OMR

Smart Card

A smart card, often the size of a credit card, contains a built-in microprocessor and memory that identify the card (and its owner) and assists in financial and other transactions.

Its primary advantage is increased security: the information can only be read by an authorized user with appropriated password.

E. Multimedia Input Devices

Voice Input Devices

A voice input device has two functions: – First, it can simply record and play back the

voice inputted by the user. – Secondly, it can record a human voice, then

with appropriate voice recognition software, convert the voice input to ASCII characters.

Digital Camera

Record images in a form that can be stored by a computer.

Some digital cameras resemble traditional cameras and are portable. Some are connected directly to a computer.

View CamDigital camera

Video digitizers

Video digitizers can capture input from virtually any type of video device, such as VCRs, televisions, and camcorders.

Audio digitizers can digitize music or voice from a microphone.

Internet References

Jan’s Illustrated Computer Literacy 101 (http://www.jegsworks.com/Lessons/lessonintro.htm)Introduction to PC (http://www.pcguide.com/intro/index.htm)Computer Hardware (http://www.ied.edu.hk/has/comp/compnent/index.htm)Tom’s Hardware Guide (http://www.tomshardware.com/guides/cpu.html)

Multimedia Tutorials (Available in SLCSS Intranet Only)

Lab 3: Input/Output Devices

Storage Devices

Storage Devices

Also called secondary storage store data & programs permanently for

future use can be used as both input & output devices

Magnetic Disk Storage

Most widely used storage medium consists of a round piece of plastic or metal,

the surface on which is covered by a magnetic materials.

e.g. floppy disks, hard disks and removable disk cartridge

Floppy Disk Random-access storage medium provides storage of 1.44MB data A circular piece of thin plastic that is coated with magnetic

material the circular piece of plastic is enclosed by a rigid plastic shell Formatting prepares a floppy disk for storage by defining

the tracks, cylinders, and sectors on the disk surface time required to locate data and transfer it to memory is

called the access time.

Data is recorded on disk in concentric circular bands called tracks. The tracks on a disk are similar to the grooves on a phonograph record. Each track is divided into pie-shaped wedges called sectors. Two or more sectors combine to form a cluster.

Data is recorded on disk in concentric circular bands called tracks. The tracks on a disk are similar to the grooves on a phonograph record. Each track is divided into pie-shaped wedges called sectors. Two or more sectors combine to form a cluster.

Most computers maintain on the disk a table with the sector and track locations of data. This table, the file allocation table (FAT), enables the computer to locate data easily.

Most computers maintain on the disk a table with the sector and track locations of data. This table, the file allocation table (FAT), enables the computer to locate data easily.

Structure of a Floppy Disk

Hard Disks Fixed in the System Unit Consists of one or more

rigid platters coated with a magnetic material

the platters, read/write heads, and the access arms that move the heads across the disk surface are all enclosed in an airtight, sealed case

Access time for a hard disk is significantly less than that for a floppy disk because a hard disk spins faster and unlike a floppy disk, a hard disk is spinning constantly (7200 revolutions per minute).

hard disks are permanently encased within the disk drive in a sealed environment free from dust and dirt. The disk can spin very rapidly, with the read/write head "floating" above the disk's surface.

Hard Disk Interfaces

To connect a hard disk to a microcomputer motherboard, you must have a hard disk interface.

This component includes circuitry that conforms to a standard recognized by both the hard disk and the motherboard manufacturer.

Common standards are Integrated Drive Electronics (IDE) and Small Computer System Interface (SCSI).

Removable Disks Provide both the storage capacity and fact

access time of hard disk and the probability of floppy disks.

Examples: – Iomega’s ZIP (100, 250, 750 MB)– Imation’s Superdisk (120MB)– Sony’s MO Disk (4~9GB)

Maintaining Stored Data

To prevent loss of data, 2 procedures should be performed regularly:– Backup

• process of creating a copy of important programs and data

– Defragmentation• process of reorganizing data stored on a disk so that

files are located in contiguous (adjacent) clusters.

CD-ROM and Optical Disks By using laser technology, optical disk can store

large quantities of data a high power laser writes data on an optical disk

by burning microscopic holes on the disk surface a lower power laser reads the data by reflecting

light off the disk surface. The reflected light is converted into a series of bits

CD-ROM– CD-Read Only Memory– can store 650 MB data– suitable for reference material such as encyclopedias, catalogs

and pictures CD-R

– CD-Recordable– write once, read many

CD-RW– CD-Rewritable– erasable; write many, read many

MO– Magneto-Optical– Floptical (Optical & Magnetic)

Magnetic Tape Consists of a thin ribbon of plastic, one side of which is

coated with a material that can be magnetized to record binary data.

A sequential storage media (must write and read records on after another)

usually cartridge tape serves as a primary means of

– backup,

– a method of transferring data between system, and

– a cost-effective way to store data that does not have to be accessed immediately

Other types of Storage Devices

PC Cards (PCMCIA) Compact Flash Memory Card Memory Stick Smart Card

Output Devices

Types of Output

Output is data that has been processed into a useful form called information.– Report– Computer Graphics– Audio Output– Video Output

Types of Output

Most output can be divided into 2 categories: Soft copy & hard copy.– Soft copy is what you see on the monitor.

Soft copy is temporary.– Hard copy can be touched and carried. Hard

copy is usually some form of paper output.

Monitors A visual output device of a computer. Monitor output is a most common form

of soft copy.

CRT Monitor Flat-panel Monitor

Resolution of Display Images on the screen are created by

configurations of dots called pixels (picture elements)

The more the pixels, the better the resolution of the image– SVGA = pixel configuration of 800 by 600 – XVGA = pixel configuration of 1024 by 768

Printers Produce permanent output (hard copy) consists of 2 main types: impact & non-

impact

Types Impact Printers Non-impact PrintersMechanisms Transfer an image by

striking the paper andthe ribbon.

Print without strikingagainst a sheet of paper.

Advantages Cheap consumables;Can print on multiplecarbon copies

Fast;High printing quality;Quiet

Disadvantages Noisy Expensive consumable

Impact Printers

Line printers– they can produce only text--no graphics.

Chain printers Dot Matrix Printers

– The most common character printers create images by using a dot pattern.

Non-impact Printers Laser Printer

– work in the same manner as copy machines; a laser beam creates electrical charges that attract toner to form an image and transfer it to paper.

Color Laser Printer

Laser Printer

Inkjet Printers– significantly less expensive than laser

printers– relatively low resolution– Electronically charged ink is sprayed

through a jet nozzle and passed through an electronic field, which deflects the ink to form a dot-matrix character

Other Output Devices

Plotter– produce high-quality line

drawings– A continuous-curve plotter

is used to draw maps from stored data.

LCD Projectors– project a computer image onto screen

Voice Output Devices– generate spoken words from text

Computer Output microfilm (COM)– records output as microscopic images on roll film.

Facsimile (FAX) Machine– transmit & receives document over telephone line.

Multifunctional Devices (MFD)– can print, copy and fax