Computer memory and its types?

Memory

Internal storage areas in the computer. The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk.
Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information.
There are several different types of memory:

RAM (random-access memory): This is the same as main memory. When used by itself, the term RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost.

                                  

•  ROM (read-only memory): Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to. 

 

PROM (programmable read-only memory): A PROM is a memory chip on which you can store a program. But once the PROM has been used, you cannot wipe it clean and use it to store something else. Like ROMs, PROMs are non-volatile.

 

EPROM (erasable programmable read-only memory): An EPROM is a special type of PROM that can be erased by exposing it to ultraviolet light.  

EEPROM (electrically erasable programmable read-only memory): An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge.

Basics of Computer ?

computer

A programmable machine. The two principal characteristics of a computer are:

It responds to a specific set of instructions in a well-defined manner.

• It can execute a prerecorded list of instructions (a program).

Modern computers are electronic and digital. The actual machinery -- wires, transistors, and circuits -- is called hardware; the instructions and data are called software.
All general-purpose computers require the following hardware components:

memory : Enables a computer to store, at least temporarily, data and programs.

mass storage device : Allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.

input device : Usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer.

output device : A display screen, printer, or other device that lets you see what the computer has accomplished.

central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions.

In addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another.
Computers can be generally classified by size and power as follows, though there is considerable overlap:

personal computer : A small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.

workstation : A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality monitor.

minicomputer : A multi-user computer capable of supporting from 10 to hundreds of users simultaneously.

mainframe : A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.

supercomputer : An extremely fast computer that can perform hundreds of millions of instructions per second.