What are the main types of memory in a computer, and explain how do they differ from one another? [HSEB 2062]

= The computer memory is a data storing devices used to either temporarily or permanently store data or instructions to be processed.
Computer memory is broadly categorized into two. They are-
(a) Primary Memory (Main Memory)
(i) RAM (Random Access Memory)
(ii) ROM (Read Only Memory)
(iii) Cache Memory
(iv) Virtual Memory
(b) Secondary Memory
(i) Hard Disk
(ii) Floppy Disk
(iii) CD-ROM etc.
a) Primary Memory: Though the CPU has calculating capability, it needs some space in which it can actually store the data or to perform calculation. This space in computer is called primary memory.
(i) RAM: It is a temporary memory which holds the data and programs during execution. The user can write, modify, erase and read the data. It is electrically dependent and the data is lost incase of power failure. Hence it is also called as volatile memory.
(ii) ROM: It is a permanent memory that holds the data necessary for the computer to become ready. The user can only read the stored data but cannot write, erase or modify the data. It is electrically independent and the data is not affected by the power failure. Hence, it is called non-volatile memory.
(iii) Cache Memory: Cache memory is used in between the CPU and the RAM and hold the most frequently used data or instructions to be processed. There are three different grades of cache. Some systems will have Level 1 and Level 2. More advanced systems will include the Level 3.
(iv) Virtual Memory: The memory which is not actually present but virtually available to support execution of large program is called virtual memory. Virtual memory combines your computer’s RAM with temporary space on your hard disk.