Chapter:1

Computer System Organization

=>Input Device: A device used to provide data and instruction to the computer are called input device.

Example: keyboard

1.Keyboard: It is used to enter both numeric al and character type data. it is like a mechanical typewriter with alphanumeric and special keys.

=>Types of Keyboard

There are two type of keyboard

1.Serial keyboard

2.Parallel keyboard

=>A serial Keyboard is one which communicates the data to the central processing unit one bit a time. that is the bit pattern that forms a particular character is sent on a single wire.

A parallel Keyboard carries one byte(8bits) at a time to the central processing unit.

The bit pattern that forms a character is sent on 8 different wires.

Microphone(MIC): It is used to record sound. It convert sound waves into audio signals.

Mouse: It is small hand held pointing device connected to CPU through a cable.

It has a rotating ball at bottom and has two click buttons on the top. As the mouse is moved across a rubber pad or a flat surface, the ball rolls and its movement is converted into electrical signal and communicated to CPU. these movements are interpreted and display on the screen as an arrow.

Output Device: When the data and instructions are fed to the computer and processed, the next step is to get the output. This output may be displayed on the monitor or printed on the paper

Many styles of trackball are

available

Monitors - Categories of Monitors

Monitors are categorized by the technology they use:

• Cathode ray tube (CRT) monitors

• Flat-panel displays

And by the way they display colors:

• Monochrome – One color on a black background

• Grayscale – Shades of gray on a white or off-white background

• Color – From 16 to 16 million unique colors

Monitors - CRT Monitors

• In CRT monitors, electrons are fired at phosphor dots on the screen.

• The dots are grouped into pixels, which glow when struck by electrons.

• In color CRTs, each pixel contains a red, green, and blue dot. These glow at varying intensities to produce color images.

• =>TFT(Thin Film Transistor) is a device within each pixel that sets the charge

Monitors - Flat-Panel Monitors

• Most flat-panel monitors use liquid crystal display (LCD) technology.

• Passive matrix LCD uses a transistor for each row and column of pixels.

• Active matrix LCD uses a transistor for each pixel on the screen.

• Thin-film transistor displays use multiple transistors for each pixel.

Flat-panel monitors take up less desk space.

Printer: A printer is an output device which is used to transfer output data from a computer onto paper.

Types of Printer There are two types of Printer

1.Impact Printer: There is mechanical contact between the print head and paper.

2.Non-Impact Printer: There is no mechanical contact between the print head and paper.

Impact Printer divided into Two parts.1.Line Printer

2.Character Printer(Serial Printer)Line Printer prints a complete line at time Types of Line Printer There are two types of Line Printer Drum Printer: a drum printer consists of a

cylindrical drum on which characters are embossed.

Chain printer: A chain printer consists of a steel band on which the characters are embossed. To print a line, the characters in line are transmitted from the memory to printer buffer.

Character printers(Serial Printer): Serial character printer print one character at a time ,with the print head moving across a line

Serial Printer divided into Two Parts.

1.Dot Matrix Printers: The printing head contains a vertical array of pins. As the head moves across the paper, selected pins free against an inked ribbon to form a pattern of dots on the paper.

2. Letter Quality Printers: The letter quality printers print full characters (continuous character not as the character mode of dots)

Non-Impact Printers: The limitations of speed in electromechanical device and cost considerations have led to the development of printers called non-impact printers.

Type of Non-Impact Printers1.Electromagnetic printers: A

magnetic image can be written on a drum surface. then this surface is passed through magnetic powder which adheres to charged areas.

The powder is pressed onto the paper.

2.Thermal Printers: An electric pulse can be converted to heat on selected sections of a printing head or on wires or nibs(heads). When this head is applied to head sensitive paper, a character is printed.

3. Electrostatic printers: The paper is coated with a non conducting dielectric material which holds charges when voltages are applied

with writing “nibs” (heads). these heads write dots on the paper as it passes. Then the paper passes through a toner which contains material with colored particles carrying an opposite charge to that written by the nibs as a results, particles adhere to the magnetized areas, forming printed characters.

4. Inkjet printers: It is a character printers, which form characters and all kinds of images by spraying small drops of ink on to the paper. The print head of an inkjet printer contains up to 64 tiny nozzles.

Laser printer: Laser printers are page printers, which print one page at a time. The main components of a laser printer are a laser beam source, a multi-sided mirror, a photoconductive drum and toner.

1.High speed 2.High quality output.1.Cost. 2.maintenance cost is high.

19

Memory• Essential component of computer, stores data, programs and

results.

• Three kinds of memory in modern computers:

1.Semiconductor 2.Magnetic 3.Optical memories

• Types of memories

1.Main memory 2.Secondary (Auxiliary) memory

ROM Memory

Static Memory

Memory

RAM Memory

Primary (Main) Memory

Masked ROM

Auxiliary (Secondary) Memory

DynamicMemory

PROM EROM EEROM

SemiconductorMemory

Magnetic Optical

RAMROM

HARDDISK

FLOPPYDISK

TAPE

CD-ROM

WORM

Speakers: Speakers receive the sound in form of electric current from the sound card and then convert it to sound format.

Memory: Memory is a device where data and instructions are Stored and retrieve.

Bit : A bits is a binary digit either a 0 or 1.

Byte: A byte is a basic unit of memory A sequence of 8 bits. Word: A sequence of 16 bits or 2 bytes.

Types of Memory

1.Main memory

2.Secondary memory

3.Cache MemoryMain memory: It is the place where the

data and instructions supplied by the input devices are stored.

It is a temporary because the data and instructions stored are eased when power cut off.

Types of Main memoryThere are two types of main

memory.1.RAM(random Access Memory)2.ROM(Read Only Memory) RAM: It is the read and write

memory. It is like a page notebook, where write something to or read something from.

Any memory location is accessed randomly for reading and writing.

It is a temporary because the data and instructions stored are eased when power Failure.

It is also known as Volatile Memory. It is Two Types 1.Static 2.DynamicBoth are volatile

RAM

Dynamic RAM made from MOS. Charge must be continually refreshed in order to maintain data. However, it is cheaper, more compact than Static RAM.

Dynamic Ram used for most primary memory. Amount of data per chip has increased rapidly.

RAM

Static RAM is expensive, but does not need to be refreshed, and is faster. Much smaller data capacity on a chip (~256 k).

Generally made using bipolar technology, although recently have developed MOS static RAM. SRAM is often used for cache memory, because of its faster access time.Rom: It is a permanent memory. The data is stored permanently and cannot be altered by the programmer. It is also known as Field Stores or Dead Stores.

Types of ROM1.PROM(Programmable Read-Only

Memory): It is initially empty. Later, the user can store programs ,data or any other information permanently. However, these programs cannot be erased once they are written to it.

2.EPROM(Erasable Programmable Read-Only Memory): The Contents stored in this can be erased by exposing it to ultra violet light source for about 10-20 minutes.

then it is progammed,that is new information can be stored.

3.EEPROM(Electrically Erasable Programmable Read-Only Memory): The contents stored in this can be erased electrically. Later new information is stored in it.

It is also known as Flash Memory. Cache Memory: It is a high speed

memory and placed between the CPU and the main memory.

Users cannot access this memory. it stores data and instructions that are currently to be executed.

Cache memory contains a copy of frequently used data/programs from main memory (ie it duplicates some contents). When the CPU attempts to read a word of memory , a cache controller checks to determine if the word is in cache.

If present then word delivered to CPU (called a hit); else (a miss) gets block from main memory and loads it into cache, preserving locality of execution.

Hit ratio is hits to total requests

There are two types of cache Memory; Level 1(L1) cache Lever 2(L2) cache The L1 Cache is built inside the CPU package

while the L2 cache is external to the CPU and resides on the motherboard.

Both L1 and L2 cache have been integrated within the cpu package to reduce access time and improve system performance further. the L2 cache on the motherboard works at motherboard bus speed while the L1 cache inside the cpu works at half the cpu clock speed.

Secondary Memory: secondary storage devices are used to store large amount of data permanently.

Types1.Floppy Disks2.Hard Disks 3.Magnetic tapes 4.Magnetic drum 5.CD-ROM

Magnetic Disks

A magnetic substance is coated on a round surfaceThe magnetic substance can be polarized in one of two directions with an electromagnet (“writing data”)The electromagnet can also sense the direction of magnetic polarization (“reading data”)Similar to a read/write head on a tape recorder (except the information is digital rather than analogue)

Floppy Disks

Also called “flexible disks” or “diskettes”The platter is “floppy”, or flexible (e.g., mylar)Most floppy disk drives can hold one diskette (two surfaces)The diskette is removableTypical rpm: 300, 360Capacities: 700 KB to 1.4 MB (& up to 100 MB “zip” disks)

Floppy Disk Example

Writeprotect tab

Spindle

ShutterAccess window

Cutawayshowing disk

Case

Hard Disk Example

Hard Disk Layout

Platter

Track

Cylinder

Drivemotor

Headmotor

Head, onmoving arm

Block

Sector

Track

Head

Head assembly

Locating a Block of Data

Seek Time Latency Time Transfer Rate

Desiredtrack

Seek

Head

TransferLatency

Note: Access time = seek time + latency

TerminologyPlatter

A round surface – the disk – containing a magnetic coating

TrackA circle on the disk surface on which data are contained

HeadA transducer attached to an arm for writing/reading data to/from the disk surface

Head assemblyA mechanical unit holding the heads and armsAll the head/arm units move together, via the head assembly

CylinderA set of tracks simultaneously accessible from the heads on the head assembly

Hard Disk: Concentric circles on the magnetized surface of the magnetic disks are known as Tracks.

Each track is dived into 8 parts. Each of the 8 parts of a track is

called a Sector.Sectors: The Tracks on the disk

surface are divided into invisible segments known as sectors.

Cylinder: Similar numbered tracks on different platters of a hard disk form a cylinder.

Digital Video Disk or Digital Versatile Disk(DVD): DVD is a optical storage device .It store more information and transfer it to the computer very fast as a CD-ROM.

DVDs come in two Formats: 1.DVD-Video Format 2.DVD_ROM Format.

NOTE: In General ,Memory refers to internal memory and Storage refers to external memory.

1Byte=8 bits. 1 MB=1024 Bytes. 1 GB=1024MB

Communication BusAddress Bus (16 lines): They carry memory address.Data Bus (8 lines): It carries data in binary form,between the processor and other external units.Control Bus: These have specific functions for coordinating and controlling micropocessor operations.