Page 45 - DCAP101_BASIC_COMPUTER_SKILLS

Basic Computer Skills

Notes
Figure 3.2: Read-Only Memory (ROM)

3.2.3 Programmable Read-Only Memory (PROM)
There are two types of read-only memory (ROM) - manufacturer-programmed and user-
programmed. A manufacturer –programmed ROM is one in which data is burnt in by the
manufacturer of the electronic equipment in which it is used. For example, a personal
computer manufacturer may store the system boot program permanently in a ROM chip
located on the motherboard of each PC manufactured by it. Similarly, a printer manufacturer
may store the printer controller software in a ROM chip located on the circuit board of each
manufactured by it. Manufacturer-programmed ROMs are used mainly in those cases where
the demand for such programmed ROMs is large. Note that manufacturer-programmed ROM
chips are supplied by the manufacturers of electronic equipment and it is not possible for
a user to modify the programs or data stored in a ROM chip. On the other hand, a user-
programmed ROM is one in which a user can load and store “read-only” programs and data.
That is, it is possible for a user to “customize” a system by converting his/her programs
to micro-programs and storing them in a user-programmed ROM chip. Such a ROM is
commonly known as Programmable Read-Only Memory (EPROM) because a user can program
it. Once the user programs are stored in a PROM chip they can be executed usually in a
fraction of the time previously required. PROMs are programmed to record information
using a special device known as PROM-programmer. However, once the chip has been
programmed, the PROM become a ROM. That is, the information recorded in it can only be
read (it cannot be changed). PROM is also non-volatile storage, i.e., the stored information
remains intact even if power is switched off or interrupted.

Figure 3.3: Programmable Read-Only Memory (PROM)

3.2.4 Erasable Programmable Only Memory (EPROM)
Once information is stored in a ROM or PROM chip it cannot be altered. Erasable
Programmable Read-Only Memory (EPROM) overcomes this problem. As the name implies,

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