lecture 14

9.1 Introduction:
We are living nowadays in a civilisation that produces a lot of information which
are intended to be stored: movies, pictures, data base concerning criminality,
information to be used for meteorological previsions, programs controlling computers
(operating systems), software in various domains of study etc…To be efficient and
reliable, the storage of those in formations should be done using systems or tools which
are resistant to corruption and are flexible. In fact, those systems should permit the
storage of huge quantity of information over a long period of time without any losses
or destruction. We should also be able to modify eventually the information stored.
Traditional tools of storage like paper (information written in books) have shown their
limits and have been replaced by new systems which are digital storage devices. Many
technologies of digital storage exist, each having advantages and also disadvantages.
9.2 General structure of digital storage systems:
All the memories, no matter their types have the same general principle of
functioning. They are surrounded by many lines having the following functions:
1. Select the address of de data within the memory;
2. Choose the type of operation which is to be achieved: read or write;
3. Lines intended to transfer the information to be written into the memory;
4. Lines intended to transfer information out of the memory…
The figure below illustrates those functions using a 32 X 8 memory. That is a
memory which is able to store 32 memory words of one byte each (1 byte = 8 bits).
Given that there are 32 memory locations, 5 address lines are needed (32 = 25).