2. COMPUTER SYSTEM
COMPONENTS
Central Processing Unit
Output
Devices
Cache
Memory
Primary
Storage
Secondary
Storage
Devices
Control
Unit
ALU
Special
Purpose
Processors
Output
Devices
Input
Devices
Short Review
Communication Devices
4. RAM or Random Access Memory
“Waiting room” for computer’s CPU.
Holds instructions for processing data, processed
data, and raw data.
Data stored in RAM can be modified . RAM is a
volatile storage . Data will lose after switching off
the computer.
Ram is measured by:
Capacity (in Megabytes or Gigabytes)
Speed (in Nanoseconds)
5.
6. MEMORY (RAM)
Amount of RAM installed will determine.
Which software applications will run (efficiently)?
How many software applications can be open simultaneously
(multitasking ability)?
RAM upgrades are cost-effective and easy to install.
All software applications will have RAM specifications
listed on their packaging.
Many applications list both a minimum and a
recommended amount of RAM necessary to run the
software.
E.g. DDRam, DDR-2 Ram
7. There is a type of memory that stores data without electrical
current; it is the ROM (Read Only Memory) or is sometimes
called non-volatile memory as it is not erased when the
system is switched off.
Data stored in ROM cannot be modified.
ROM works slower than the RAM memory.
ROM is a non-volatile storage . Data remains unchanged
even after switching off the computer.
E.g. EPROM, EEPROM
8. Secondary storage is computer memory that is not
directly accessible to the CPU of a computer,
requiring the use of computer's input/output
channels.
It is used to store data that is NOT in active use.
It is usually slower than primary storage but it
always has higher storage capacity. It is non-
volatile.
Data remains unchanged even after switching off
the computer.
9. Magnetic Storage
stores data by magnetizing
microscopic particles on the
disk surface.
Examples: floppy disk,
hard disk, tape
Optical Storage
data is read using laser light and
is possible to see data
through a high powered
microscope.
Examples CD and DVD
11. Floppy Disks
Diskettes or floppies
Capacity 1.4MB
3½ inch disk
Labeled 2HD data can be saved on both
sides
Portable storage media
Floppy disk drives (FDD)
12. Parts of a Floppy
Shutter slide - metal component that opens
when disk is inserted in the drive.
Labels - applied to external surface to identify
contents.
Write-protect notch - when open, prevents
data to be written to the disk.
Protects the disk from accidentally writing over it.
14. Hard Disks
Use thicker, metallic platters for storage
Faster than a floppy diskette
Speed is measured in rotations
or revolutions per minute (rpm)
Large capacity
Sensitive instruments
15. Types of Hard Disk
There are three different types of hard disks;
internal hard disk
hard disk cartridge
hard disk pack
All disks use a file system (File Allocation Table) to
keep track of the names and locations of files that
reside on a storage medium.
16. Internal Hard Disk
Located inside system unit
Known as a fixed disk
Designated as the C drive
Advantages over floppies
Access speed
Capacity
17. Optical Disks
Are permanent storage media that use
laser technology to store data.
Optical disks can be 3½ , 4¼ , 5¼ ,8, 12
and 14 inches.
Most common size is 4¾ and is stored in
a jewel box.
Two common formats are:-
CD - Compact Disk
DVD - Digital Versatile Disk or Digital Video
Disk
19. Compact Disc
CD-ROMs
read only - cannot be written on or erased by the user.
used to distribute databases, reference and software.
Write once - CD-R
can be written to once but can be read many times
(WORM).
CD burners are used to write data onto the disk.
Rewritable - CD-RW
erasable optical disk, write many times, read many times.
Disk surface is not permanently altered so can be written to,
erased and written again.
20. Digital Versatile Disc
Digital Versatile Disk or Digital Video Disk
(DVD)
Similar to CDs, but can store more data [can
store 4GB to 17GB of data]
Types
Read only
Write once
Rewritable
21. Other Type of Secondary Storage Devices
USB Flash Drives
They are flash memory data storage devices
integrated with a USB interface.
They are typically small, lightweight, removable and
rewritable .
Data capacity: 512MB, 1GB, 2GB, 4GB, etc.
22. Flash memory cards
Widely used in notebook computers,
Cell phones, etc.
Used to record MP3 music files
Magnetic tapes
External storage
Provides sequential access
Information stored in sequence
Slower than disks which provide direct access
Other Type of Secondary Storage Devices
23. TYPES OF ROM
PROM (Programmable Read only Memory): it uses fusible links that
can be burned by using special PROM burning circuit. It can be
programmed by the user using a PROM programmer.
EPROM (Erasable Programmable Read only Memory): the information
stored in an EPROM can be erased by exposing the memory to
ultraviolet light.
EEPROM (Electrically Erasable Programmable Read only Memory): it
is also same as EPROM but the erasing is done by electrical signals.
24. TYPES OF RAM
SRAM (Static RAM): It uses flip flops for storage elements. In
SRAM once data is written into memory location, the data stays
unchanged unless some new data is entered into that location.
DRAM (Dynamic RAM): It uses capacitors as storage element. The
dynamic RAM contents may change with time due to leakage of
charge. So it is required to refresh the storage elements
periodically. It consumes less power compare to SRAM.
