Computer Knowledge - Exam Oriented
1. Different Type of Memories
Memory devices have various characteristics depending on their principle, system and material.
Read only memory (ROM) and read/write memory - In read only memories (ROM), data is written only once and it can�t be changed thereafter but it can only be retrieved (read). In read/write memories, data can be stored, read, erased-and rewritten as desired.
Read and write memories include integrated circuits (bipolar or Metal oxide semiconductor), magnetic thin film (wire or plate), magnetic core, magnetic drum (fixed head or moving head), magnetic disk (fixed lied or moving head), disk pack, magnetic tape and delay line. ROM includes IC (bipolar or MOS), magnetic thin film (wire or plate), magnetic material (UI core or ring core), capacitor, resistor, punch card and. punch tape.
Random access memory (RAM) and Serial Memory - In RAM, any word can he accessed in same time but in sequential (Serial) memory (such as disk, drum, tape) data is available sequentially, only in the same sequence as originally stored and thus more time is required to search it.
Volatile and non-volatile memories - A non-volatile memory is one that retains its contents even if power supply fails (as with ferrite core, drum, disk and tape memory). Volatile memory is one which loses its contents on electric failure (semiconductor type memory).
Destructive and non destructive memory - In the case of destructive memory, its contents get lost when it is read and thus to save the memory it has to be rewritten automatically after read operation. In non-destructive memory, the contents are retained even after reading operation. Core memory is destructive read out type and IC, drum, disk and tape are non destructive read out type.
Static and dynamic memories - In a static memory, the contents are retained indefinitely as long as system supply power is applied. Dynamic memories usually store a binary digit as charge on a capacitor which will discharge after some time. It, therefore, needs refreshing periodically by a clock control which reads the cell content and rewrites it.