1.8 PRINTERS
An output device that
produces text and graphics on a physical medium.
1.
Quality
type : Letter quality or draft quality.
2.
Speed
: Characters per second (CPS) or pages per minute (PPM),
3. Impact
or Non-Impact :Impact printer is dot-matrix printer(striking
ink ribbon).
Non-impact
printers are ink-jet printers and laser printers(non striking mechanism).
4.
Graphics
:
Some printers can print only text. Other
printers can print both text and
graphics.
5.
Fonts
:
Some printers, like dot matrix
printers, are limited to one or few
fonts.
Laser
and ink-jet printers are capable of
printing variety of fonts
1.8.1 specifications of some printers :
PRINTER
|
PRINTING SPEED
|
BUFFER SIZE
|
DOT MATRIX
|
30-300CPS
|
1K-64K
|
INK-JET
|
1-12PPM
|
1MB-4MB
|
LASER
|
4-24PPM
|
4MB-32MB
|
Line printer : Contains a chain of characters or pins that print an entire line at one time.
Thermal printer :
i)pushing heated pins against
heat-sensitive paper.
ii)Widely used in calculators and fax machines.
1.9 KEYBOARD
i)Key
boards are designed to input text and characters.
ii)An arrangement of rectangular
buttons.
iii)Characters printed on the keys.
iv)Types of keys are
alphabet,numerical,special and functional.
v)Multimedia and internet keyboards
are available.
1.10 MOUSE
Controls
the movement of cursor or pointer on a display screen.
1.
Mechanical
: i)Has
a rubber or metal ball on its underside that can roll in all directions. Ii)Mechanical
sensors within the mouse detect the directions and move the cursor.
2.
Opto-mechanical:
Uses optical sensors to detect motion of the ball.
3. Optical: i)Uses
a laser to detect the mousers movement
ii)They
respond more quickly.
Mouse
can be connected to the compute in one of the following ways :
1.
Serial
mouse: They are connected directly to an RS-232C serial
port or a PS/2 port.
2.
PS/2
mouse: They
are connected to a PS/2 port.
3. USB mouse:
They are connected through USB port.
4. Cordless mouse:
i) No physical connection.
ii)Instead they
rely on infrared or radio waves to communicate with the computer.
1.11 MONITOR OR VIDEO
DISPLAY UNIT (VDU)
Monitors provide a visual display of
data.
1. Monochrome:
i)Display two colors. One for the back ground and one for the foreground. ii)Colors
can be black and white or Green and black.
2. Colors: i)
Display 1 million colors
Characteristics/Features
of a monitor
1.
Refresh data:
i)How many times per second the screen is refreshed.
ii)
To avoid flickering, the refresh rate should be at least 72 Hz.
2. Interlaced or non interlaced:
Resolution Rate
3. Convergence:
The clarity and sharpness
1.12 RANDOM
ACCESS MEMORY
i)To store the data while using.
ii)Volatile memory.
iii)Constant current is required to
retain the information.
1.12.1 Types of RAM
1. Static RAM: i)Has multiple transistors
for each memory cell.
ii)Need not be refreshed.
2. Dynamic RAM:
Need to be refreshed.
3. SDRAM:
i)Synchronous Dynamic Random Access
memory.
ii)Synchronized to the system clock.
iii)Has the ready-data when the CPU requests it.
iv)Increases the efficiency by reducing
CPU waiting time.
4.DDR-RAM: i)Double
Data Rate SDRAM.
ii)Data transfer rate is double
1.13 SECONDAAARY OR AUXILIARY
STORAGE DEVICES:
1.13.1 Floppy disk drive (FDD): i)To record the data.
ii)Sizes are 8’’, 5.25”, and
3.5”
iii)Can store
approximately 1 million characters.
1.13.2 Compact Disk :
i)An optical disc used
to store digital data.
ii)Types are
CD-R and CD-RW.
iii)Can store
approximately 700 MB of data
DVD (digital versatile disc or
digital video disc :
Can store approximately 4.7
GB of data
A Blu -Ray Disc(BD)
i)A single layer blu-ray Disc
can store 25 gigabytes(GB).
ii) A dual layer blu-ray Disc
can store 50 GB.
ii) Rotational speed is 7200 rpm
iii)Types are,.
1.
Small
Computer System Interface(SCSI) HDD : For high end users or
servers.
2.
Integrated
Disk Electronics (IDE)HDD : Standard
in today’s computer.
3.
SERIAL
ATA (SATA) : i)Have
large capacity. ii)Have fast transfer rates.
4.
EXTERNAL
HDD : Backup disk.
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