RAM and ROM

1. RAM (Random Access Memory) :

This is a part of computer's local memory, where the computer stores all the data and instructions it receives from input and the results as it works through its calculations.

RAM is short-term memory or volatile memory, i.e., when the computer is switched off, all the information disappears, whereas ROM is permanent memory. The random access memory requires very little time for access to each data and is considered to be the fastest memory. Generally, magnetic core memories and semiconductor memory systems fall in this category.

Each bit in a RAM stores information by means of electric charge, where the presence of an electric charge indicates a '1' and the absence a '0'. One variety of RAM is the so-called Dynamic RAM, where this electric charge tends to leak out in a few milliseconds, so that the information present in the RAM is lost (like a leaky tin which can hold water only for a short while).

Consequently, the sets of information stored in such RAMs need be refreshed periodically, before all the charge has leaked out. For this purpose, special refresh circuitry has to be provided. As against this, we have Static RAMs, which are not leaky and therefore do not require any refreshing.

They also tend to be faster, a typical Static RAM today has an access time of 80 nsec which means that it could take 80 nsec to read or write into any location. The Dynamic RAM is 120 to 120 nsec. However Static RAMs tend to be more expensive than their Dynamic counterparts and are not used for large memories.

2. ROM (Read Only Memory) :

It is permanently in-built in the computer at the time of its production. ROM is otherwise called firmware also. It stores a set of instructions permanently which instructs the computer how to work. In ROM, permanent data and programs like trigonometric and logarithmic functions are also stored. In one variation of this type of memory , known as Programmable Read Only Memory (PROM), the flexibility of data alteration is also provided.