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Memory
A memory unit is a device to which binary information is transferred for storage and
from which information is retrieved when needed for processing.
(a) RAM → random -access memory with both read & write operations.
Examples are: Static RAM (SRAM), Dynamic RAM (DRAM).
(b) ROM → read-only memory with read operation only. Examples are:
PROM, EPROM, EEPROM.
A memory stores information in groups of bits called words. A memory word is a
group of 1s and 0s. A group of 8 bits is called a byte. Most computer memories use
words that are multiple of byte. The capacity (size) of memory is usually stated as
total number of bytes that the unit can store.
2 10 =1K, 2 20 =1M, 1G=2 30 ……..2 16 =...K; 2 21 =...M; 2 32 =….G.
“the number of address lines k is independent of the number of bits in each word”.
Read Only Memory (ROM)
A ROM is considered a programmable device where binary information can be stored
and kept even when power supply is switched off. A ROM consists of a decoder and
array of fused (programmed) OR gates. This is shown in the following Figure.
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