MEMORY.

There are two main types of memory inside the computer.

Read-only-memory (ROM) is a chip or a group of chips containing programs, tables of constants and instructions for the CPU. Only the CPU has access to this memory. For example, when we turn on the computer, the CPU gets its first instructions from the ROM. These instructions are burnt into the chip with the help of special equipment before the chip is installed inside the computer. Users do not have access to the ROM, so they can't change these instructions.

Users work with the random-access-memory (RAM). RAM is a collection of cells and we can access any cell at any given time, hence the name random access memory.

RAM is often referred to as main memory or primary storage. RAM usually occupies a number of chips connected together. It is used to store programs and data being used by these programs while the computer is on. When the computer is turned off any information is erased from the RAM. That is why RAM is often called volatile while ROM is a non-volatile type of memory.

Every cell in the memory is assigned a unique number called a memory address. It is hard to remember memory addresses as numbers so many programming languages allow to refer to cells with alpha-numeric names. For example, when the computer gets the instruction NUMBER1=3, it allocates a free cell in the primary storage, names it NUMBER1 and writes 3 in it. From that moment this cell is occupied by 3 and we can read its content many times using the cell name NUMBER1 as a reference to it in different instructions. Every time we refer to the cell, the copy of its content is used by the instruction. So we write data once but we can read it many times until it is overwritten by something else.

Today computers are sold with at least 4M of RAM, although some packages (e.g. Windows 95, Delphi 2.0) require 8M or more. Other packages run on 4M but very slow, e.g. Powerpoint 4, Access 2. The speed of processing depends not only on the clock rate of the computer but also on the size of RAM. The bigger the size of RAM the quicker your computer will work. 32-bit processors can theoretically address up to 4G of memory, but even with modern technologies memory this big will not fit in the computer case. Also today's software doesn't require so much memory. In reality Pentium and Pentium Pro processors work with RAM up to 256M.

If you want to know more about RAM technologies and how to upgrade RAM click on RAM: Factors to consider.