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RAM

RAM is the main place for storing instructions and data whilst a program is being executed. It is also called main memory. Program data is copied into RAM before the CPU can run the program.

RAM is usually measured in gigabytes. The more gigabytes of RAM a computer has, the more programs and operations it can handle at the same time.

Typical computers might have the following RAM:

Each unique memory location in RAM holds one word of information. Every memory location has a unique address so that once data has been stored there it can be found again later when it's needed. RAM also has a word size measured in bits to indicate the size of the memory locations.

Word size

The word size of the machine is how many bits its CPU can manipulate in one go.

The amount of data that a CPU can manipulate with one machine code instruction or transfer over a bus is measured in bits. When you look up the CPU specifications of any computer or games console, you will find out if it is a 32-bit, 64-bit or 128-bit machine.

A CPU with a 64-bit word size can process 64 bits using one single machine code instruction. This is twice as many bits as a 32-bit CPU.

Increasing the word size means more data can be manipulated at a greater speed. It also means that the CPU can keep track of a larger range of memory locations.

DRAM and SRAM

There are two types of RAM: dynamic RAM and static RAM.

  • Dynamic RAM (DRAM) uses a transistor and a capacitor to represent and store a bit of data. The charge needs to be refreshed every few seconds.
  • Static RAM (SRAM) uses a group of transistors combined for each bit of data. They do not lose the charge while in use so SRAM is much faster than DRAM. SRAM technology can be non-volatile when used for flash memory in storage and ROM.

DRAM is usually used for the main RAM memory. SRAM is used for cache memory. Static RAM is more complex to build and much more expensive than DRAM.