RANDOM ACCESS MEMORY (RAM):

The RAM-type memory will allow data to be written into it, as well as read from it. With very few exceptions, RAMS lose their contents when the power is removed and are thus known as "Volatile" memory devices.  All computers use RAM to store data and programs written into it either from keyboard, or external sources such as magnetic tape/disk devices.

RAMs are often described in terms of the number of bits, i.e. 1s and 0s, of  data that they hold, or in terms of the number of data words, i.e. groups of bits, they can hold.  Thus a 16384 bit ram can hold 16384 1s and 0s.  This data could be arranged as 16384 1-bit words, 4096 4-bit words or 2084 8-bit words.  Semiconductor memories vary in size, e.g. 4K, 64K, 128K, etc.  Hence we are using K defined as:

K =2¹⁰ = 1024

Thus a 16K memory has a storage capacity of 16 X 1024 = 16384 words, a 128K memory 0f 1310672 words and so on. There are two main members of the RAM family:

• Static RAM.
• Dynamic RAM.

The essential difference between them is the way in which bits are stored in the RAM chips.  In a static RAM, the bits of data are written in the RAM just once and then left until the data is either read or changed.  In a dynamic RAM, the bits of data are repeatedly rewritten in the RAM to ensure that the data is not forgotten.