Download A serial Keyboard

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.
Many styles of
trackball are
available
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
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 Printers
1.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.
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
Memory
Primary (Main) Memory
RAM Memory
Static
Memory
Auxiliary (Secondary) Memory
ROM Memory
Dynamic
Memory
Masked ROM
PROM
EROM
19
EEROM
Semiconductor
Memory
Magnetic
Optical
WORM
RAM
RO
M
HARD
DISK
CD-ROM
FLOPPY
DISK
TAPE
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 Memory
Main 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 memory
There 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.Dynamic
Both 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 ROM
1.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.
 Types
1.Floppy Disks
2.Hard Disks
3.Magnetic tapes
4.Magnetic drum
5.CD-ROM
Magnetic Disks
A magnetic substance is coated on a round
surface
The 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 removable
Typical rpm: 300, 360
Capacities: 700 KB to 1.4 MB (& up to
100 MB “zip” disks)
Floppy Disk Example
Access window
Shutter
Cutaway
showing disk
Case
Spindle
Write
protect tab
Hard Disk Example
Hard Disk Layout
Head
Block
Head
motor
Platter
Sector
Track
Cylinder
Track
Drive
motor
Head
assembly
Head, on
moving arm
Locating a Block of Data
Seek Time
Latency Time
Transfer Rate
Latency
Transfer
Head
Seek
Desired
track
Note: Access time = seek time + latency
Terminology
Platter
A round surface – the disk – containing a magnetic
coating
Track
A circle on the disk surface on which data are contained
Head
A transducer attached to an arm for writing/reading data
to/from the disk surface
Head assembly
A mechanical unit holding the heads and arms
All the head/arm units move together, via the head
assembly
Cylinder
A 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 Bus
Address 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.