2. ROM
• ROM is short for Read Only Memory.
– It is permanent, long-term memory which
cannot be erased or changed in any way;
– It is also known as “Non-Volatile Memory”
because it doesn’t disappear after the
computer is switched off.
3. ROM cont’d
• ROM chips instruct the
computer how to load the
operating system from
the hard drive into the
computer’s memory.
• Don’t confuse the hard
drive with ROM – the
hard drive is an internal
backing store (storage
device).
4. RAM
• RAM (Random Access Memory) is:-
– Temporary, short-term working memory;
– Only works when the computer is turned on;
– It is also known as “Volatile Memory” because data
disappears if the power is switched off.
• Each time you start a program e.g. MS Word, it is
loaded into RAM.
• The amount of RAM influences processing power, speed
and how many programs can run at the same time.
– Many computers are now sold with 128 or 256 MB of
RAM.
5. Measurement of Memory
• Computer memory is measured in bytes. A
single byte is made up of a series of 1's and
0's, which are known individually as binary
digits or “bits”.
• This is the way the computer communicates and
stores information. With each keystroke or
character a byte of memory is used.
– 8 bits = 1 byte
– 1024 bytes = 1 kilobyte
– 1024 kilobytes = 1 megabyte
– 1024 megabytes = 1 gigabyte
6. Data Storage - Internal
Backing Store
• Hard Disks are the main internal backing store
usually found inside computers.
• The main benefit of hard drives is that they
have a large storage capacity – 20 gigabytes or
more. (1 Gb = 1024 Mb).
7. External Backing Store
• Floppy disks are a common external
backing store, however only store up to
1.44 Mb of data.
• When are they useful?
– Excellent for transferring small files of data
from one machine to another and for backing
up important small files stored on your hard
disk.
8. External Backing Store
• CD-ROM (Compact Disk Read Only Memory)
disks are optical disks that use the same
technology as musical compact disks.
• They store up to 700 Mb of data and a laser
beam is used to read the data off the disk.
• What can they be used for?
• As CD-ROMs are much bigger than floppy
disks, they can be used for multimedia
applications such as encyclopaedias and can
store pictures, sounds and video clips.
9. 3.5 inch Floppy Disk
Head Contact
Area Positioning &
Drive Hole
Metal Hub
Centre Hole
Disk inside
plastic case Write Protect
Notch
