FREE online courses on the Basics of a Computer - MICROCOMPUTER - Memory
Memory can also be contained on a
chip which like the microprocessor chip is very small and cheap to manufacture
when produced in large volumes. Memory may also be assembled on the same chip as
the MPU but for the purpose of our description the memory is treated as a
separate entity.
There are various types of memory
chips and a single microcomputer might utilize more than one type. The most
common is random access memory. Like the memory of the traditional computer,
information can be 'read' from a RAM chip and 'written' to it. When switched
off, any information stored in the memory is lost. RAM behaves exactly as the
Main memory.
Another type of microcomputer
memory is read only memory. Information is 'brunt' into the ROM chip at
manufacturing time. It cannot be altered and fresh information cannot be
'written' into a RAM. The information can be 'read' and transferred for use
elsewhere, for example to a RAM. When the power supply is switched off, the bit
patterns in the memory are not lost as they are in the case of the central
memory of a computer or a RAM chip. ROMs are used for applications in which it
is known that the information never needs to be altered, for example the
operating system software which controls the use of a complete microcomputer
system or a monitor program for controlling a washing machine.
A variation of the ROM chip is
programmable read only memory. PROM can be programd to record information using
a facility known as a prom-programr. However, once the chip has been programd
the recorded information cannot be changed, i.e. the PROM becomes a ROM and the
stored information can only be 'read'. PROM is also non-volatile storage.
A fourth type of memory is
erasable programmable read only memory. As the name suggests, information can be
erased and the chip programd anew to record different information using a
special prom-programr facility. ERASURE is achieved by exposing the chip to
ultraviolet light. When an EPROM is in use information can only be 'read' and
the information remains on the chip until it is erased.
