Computer

A machine that can be programmed to accept data (input), process it into useful information (output), and store it away (in secondary storage device) for safekeeping or later reuse

Process is directed by software but performed by the hardware

Computer System

People

Software

Hardware

People

Computer programmer – person who writes programs

Users or End-users – make use of the computer’s capabilities

Software

Programs

Set of instructions that directs the hardware to do a required task and produce the desired results

HardwareBasic Components of a Computer

Function of Computer System

Data handling

I Input

P Process

O Output

S Storage

Function of Computer System

Computer Organization

A Typical Von-Neumann Architecture

1. Input unit2. Output unit 3. Memory unit 4. Arithmetic and logic unit (ALU) 5. Central processing unit (CPU) 6. Secondary storage unit

Control Circuit(ex: PC: Program Counter)

ALUMemory I/O

CPU

Six logical units in every computer:

1. Input unit Obtains information from input devices

(keyboard, mouse)

2. Output unit Outputs information (to screen, to printer, to

control other devices)

3. Memory unit ROM (Read Only Memory) RAM (Random Access Memory)

Six logical units in every computer (cont):

3. Arithmetic and logic unit (ALU) – part of CPU Performs arithmetic calculations (addition,

subtraction...) and logic decisions

4. Control unit (CU) - part of CPU Supervises and coordinates the other sections

of the computer

5. Secondary storage unit Cheap, long-term, high-capacity storage Stores inactive programs

Sources of Data for the Computer

Two types of data stored within a computer: Original data or information: Data being introduced to a

computing system for the first time. Computers can deal directly with printed text,

pictures, sound, and other common types of information.

Previously stored data or information: Data that has already been processed by a computer and is being stored for later use. These are forms of binary data useful only to

the computer. Examples: Floppy disks, DVD disks, and music

CDs.

Two Types of Storage

Secondary storage

long-term storage

Primary storage or memory

temporary storage

Memory

Main memory store programs and data store temporary results store the output that will be transmitted

to backing stores / output devices 2 types

Read-Only Memory (ROM) Random Access Memory (RAM)

Comparison between RAM and ROM

RAM ROM

Data can be read fromor written intomemory

Data can only be readfrom memory

Volatile (data will belost after the power isoff)

Non-volatile

Store user programs Store system programs

Pictorial Representation of Memory

0

1

2

3

:

address main memory

Pictorial Representation of memory location

cell

Each memory location has many cells and can only store 0 or 1

memory

location

For 8-bit computer, there are 8 cells in one memory location or 8 BITs ( 1 byte)

Example

Each memory location has 16 cells

memory

location

It is a 16-bit computer, there are 16 BITs (2 bytes)

Wordlength

word a memory location to store an

information wordlength

number of bits in one memory location

Example

memory

location

wordlength = 16 bits

Size of a memory

number of memory locations limited by the number of bits to

represent an address

Example

no. of bit(s) to store an address = 1

max. no. of memory locations = 2

0, 1

01

Example

no. of bit(s) to store an address = 2

max. no. of memory locations = 4

00, 01, 10, 11

00011011

Example

no. of bit(s) to store an address (n) = 3

max. no. of memory locations (M) = 8100, 101, 110, 111

000001010011100101110111

000, 001, 010, 011,

In conclusion M = 2n

Units in main memory smallest basic unit = bit basic unit = byte (B) (1 byte = 8 bits)

1 Kilo (K) =2 10

1 Mega (M)= 2 20

1 Giga (G) = 2 30

For example1 MB = 1 megabyte = 1 x 2 20 bytes = 1048576 bytes

Memory / Primary Storage

Temporary storage

Holds input to be processed

Holds results of processing

Contains the programs to control the computer and manipulate input into output

Volatile

Secondary Storage

Long-term storage Non-volatile

Secondary Storage Examples Magnetic disks – read and written by

magnetic disk drive Hard disk Diskette

Optical disks – read and written by optical disk drives CD-ROM DVD-ROM

Magnetic tape – read and written by magnetic tape drives Primarily used for back-up

Memory

A large collection of circuits, each capable of storing bit

Cells (words): manageable units; typical size is 8 bits (1 byte), some machines are 16 bits (2 bytes) and some are 32 bits or 64 bits Byte (8 bits), KB (kilobyte, 103 210

bytes), MB (Megabyte, 106 220 bytes), GB (Gigabyte, 109 230 bytes). Note: k ≠ K because 1000 ≠ 1024.

Memory

Computer memory is comparable to a collection of numbered mailboxes. To identify individual cells in a machine’s main memory, each cell is assigned a unique name, called its address

The organization of byte-size memory cell

Memory

...01001000 01100101 01101100 0110111101101100 00101110

H e l l o ,ASCII

...Data

Address 0000 0101 0000 0110 0000 0111 0000 1000 0001 0001 0001 0010

Address BusData Bus

0 0 0 0 0 1 0 1 Low-order endHigh-order end

Least Significant Bit (LSB)Most Significant Bit (MSB)

Data Storage Information stored away for use later on

(like food in the refrigerator) Usually long-term (safer) May be stored on disks, CDs. DVDs, or

flash drives

Measuring Information

Bytes One character takes up about one Byte. An email takes up a few (thousand

bytes) Kilobytes (thousands of bytes) A picture may take up Megabytes

(millions of bytes) All the information on a computer may

run into Gigabytes (billions of bytes)

Disks Floppy Disk

Holds 1.44 Megabytes 1,440,000

Bytes Feels hard

Floppy part inside cover

Almost obsolete

Hard disks

Hard Disk Main disk for

most computers Holds Windows,

software, and most data

Usually don’t see it because it’s inside computer.

Platter Read/Write head

Hard Disks

Most common and important form of storage today

Hard disks are high-speed, high-capacity storage devices

They contain metal disks called platters

They contain two or more stacked platters with read/write heads for each side

Disks and Disk Drives

sectorseach track is divided into pie-shaped wedges

clustertwo or more sectors combined

tracksdata is recorded in concentric circular bands

Disks and Disk Drives

Magnetic Disks are coated with a sensitive material that

permits the placement of magnetic charges on its surface

positive charges = 1 bits, negative = 0 Magnetic Disk Drives

include read/write head(s) to read and write magnetic charges, the mechanism to spin the disk(s), logic to determine where the read/write head needs to be

How the Disk Drive Works

Computer transmits info to disk drive: the file name read or write command Information to write (if a write) or Location in memory to move info (if

read) The disk drive spins the disk

Hard disks spin as fast as 10,000 rpm! The read/write head is repositioned to

the proper location

How the Disk Drive Works

The read/write head actually floats above/below the disk on a cushion of air created by the fast rotation of the disk Distance of separation is 1/300 the

width of a human hair!

How the Disk Drive Works

The time to reposition the head is known as the positioning performance, and is determined by:

seek time – time to move read/write head to the right track

latency – time to rotate the disk until the right sector is underneath the head

read/write head

dust hair fingerprint

Factors Affecting a Hard Disk’s Performance

Seek time or positioning performance – How quickly the read/write head positions itself and begins transferring information. It is measured in milliseconds (ms)

Spindle speed or transfer performance – How quickly the drive transfers data. It is measured in rotations per minute (RPM)

More on Hard Disks

Head crash – a sudden movement could cause the read/write head to touch the disk’s surface this can ruin the head, the disk, and/or the data

stored there Hard Disk Longevity – hard disks fail more

often than any other computer component because of head crashes, rapidly moving parts, and

high degree of usage but, because of our reliance on hard disks,

redundancy is very desirable

Floppy and Zip Disks and Drives

A disk or diskette is a portable storage medium

High-density floppy disks that are commonly used today store 1.44 MB of data

Disks work with a disk drive Zip disks store up to 750 MB of data

and are not downwardly compatible with floppy disks

Zip DriveFloppy Drive

Floppy Disk

CD-ROM Discs and Drives

CD-ROM stands for Compact Disc-Read Only Memory

CD-ROM drives can not write data to discs

They are capable of storing 650 MB of data

They are used for storing operating systems, large application programs, and multimedia programs

CD-R and CD-RW Discs

CD-R Discs can be read

and written to Discs can only be

written to “once” CD-R drives are

capable of reading and writing data

CD-RW Discs can be read and

written to Discs are erasable Discs can be written to

many times CD-RW drives are

capable of reading, writing, and erasing data

DVD-ROM Discs and Drives

DVD stands for Digital Video Disc

DVD technology is similar to CD-ROM technology

DVDs are capable of storing up to 17GB of data

The data transfer rate of DVD drives is comparable to that of hard disk drives

DVD-RW and DVD+RW Discs

DVD-R and DVD+R drives have the ability to read/write data

DVD-RW and DVD+RW drives allow you to write, erase, and read from a disc many times

Optical Storage

In this form of disc, the information stored on this media is accessed using lasers Information is stored as pits Pits are created by burning them into the surface of the disc Information is accessed by shining a laser at the surface of

the disc Light is reflected if there is no pit, or swallowed if there is a

pit This is very different than magnetic charges which are

fragile (corruptible) So optical discs are much more robust than magnetic

storage

Optical Storage

Notice that once burned onto the disc, there is no way to remove a pit (burn mark)

So most forms of optical storage are read-only or write-once This is a CD-ROM (factory produced) or CD-R (recordable) A different technology (and more expensive) offers CD-RW –

data can be recorded and erased so that you can re-write onto the disk

Surface of a CD-ROMor CD-R (pits formedby burn marks)

Magnetic Tape

Tape was the primary form of storage for decades Used since the 1950s and still in use today even though

disks were introduced in the 1960s

Quarter-inchcartridge anda tape drive

This $15 cartridge can store 10 Gbytes!

Magnetic Tape

Tape uses sequential access

To find a file, start at the beginning of the tape and fast forward until you find the right location

Can be very time consuming as tape can be very long (some are 2400’ long)

Tape cannot reuse freed up space from a deleted file, unlike a disk

Compare using a cassette or videotape vs. CD or DVD

So we use tape mainly for backups and archives only since tape is very cheap for the amount we can store

Flash Drive

Most recent widely used storage system

Very portable, often worn like jewelry 128-512 Megabytes most common

sizes

The Processor

Central Processing Unit (CPU)

Converts data to useful information

Interpret and execute instructions

Communicate with input, output and storage

The Central Processing Unit

The Central Processing Unit ( CPU) Often referred to as the “brain” of the

computer. Responsible for controlling all activities

of the computer system.

The Central Processing Unit

The three major components of the CPU are:1. Arithmetic Unit (Computations performed)

Accumulator (Results of computations kept here)2. Control Unit (Has two locations where numbers are

kept)Instruction Register (Instruction placed here for analysis)Program Counter (Which instruction will be performed next?)

3. Instruction Decoding Unit (Decodes the instruction)

Motherboard: The place where most of the electronics including the CPU are mounted.

Central Processing Unit (CPU)

“brain” of a computer, consisting of Arithmetic and logic unit (ALU): performs arithmetic

calculations (addition, subtraction...) and logic decisions (>, <, =, ...)

Control Unit (CU): decodes each machine instruction and sends signal to other components for carrying out the instruction.

An integrated circuit (IC) that is a full central processing unit is called a microprocessor (p); a CPU’s current instruction and data values are stored temporally inside the CPU in special high-speed memory location called registers.

CPU speed: ? MHz (M: Mega = 106, Hz=1/sec);

CPU

Control unit (CU) control the data flow control the operation of other

components in the computer Arithmetic and logical unit (ALU)

perform arithmetic operations (e.g. +, -, *, / ..)

perform logical operations (e.g. AND, OR, ..) CU + ALU = Processor

What is in the box? Motherboard

Typical parts of a motherboard.

ABIT SE6

Disk capacities Floppy: 1.4 MB Hard disk: 20 GB – 160 GB

CD 700 - 800 MB

DVD 4.7 GB

17 GB

1 KILOBYTE = 1000 BYTE 1 MEGABYTE = 1000 KB1 GIGABYTE = 1000 MB

Input devices

Accept data or commands and convert them to electronic form

Getting data into the computer Typing on a keyboard

Pointing with a mouse

Scanning with a wand reader or bar-code reader

Terminal

Output devices

Monitor or screen Text Numbers Symbols Art Photographs Video

Printer Black and white Color

• Convert from electronic form to some other form

• May display the processed results

• Usable information

Network Definition

A system that uses communications equipment to connect computers and their resources.

Types Local area network (LAN) – connects computers in

close proximity Metropolitan are network (MAN) – connect computers

between buildings in the same geographic area Wide are network (WAN) – connects computers over

great distances

Home Connectivity

Connect home PC to other computers

Use modem to convert signals between electronic (computer) and analog (voice) formats

Internet Collection of networks No ownership No central source for services available No comprehensive index of what information is

available

Individuals

Businesses

Organizations

Libraries

Research labs

Government

Connects Everyone!

Getting Connected

Internet – What Can You Do?

WWW – World Wide Web

FTP – File Transfer Protocol

E-mail

UseNet

IRC – Internet Relay Chat

Bulletin Boards

World Wide Web• Browser – program that allows the user to

move around and explore the Internet

• Use the mouse to point and click on text and graphics

• Web page

• Web site

• Home page

Classifications of Computers Use the computer that fits your needs Based upon

Size Speed Cost Portability Number of simultaneous users supported Available software Typical use

Personal Computers Other names

PC Microcomputer Home computer

Categories Low-end functional Fully powered Workstations Net computer or net box (Web TV)

Desktop Models

Notebook Computers

Portable Lightweight Fits in a briefcase Battery operated

Laptop Larger Heavier

More expensive that desktop models

Data and Information

All computer processing requires data, which is a collection of raw facts, figures and symbols, such as numbers, words, images, video and sound, given to the computer during the input phase.

Computers manipulate data to create information. Information is data that is organized, meaningful, and useful.

During the output Phase, the information that has been created is put into some form, such as a printed report.

The information can also be put in computer storage for future use.