MemoryMemoryMemory is also known as: Main Memory Primary Memory or Primary Storage

The reason that it is referred to as main memory is because it is the main location where the CPU looks for data and instructions during execution of a program.

Memory can be thought of as a series of cells which can contain data or instructions. Each cell has a distinct address. Typically a cell can store 8 bits (a byte) of information.

MemoryMemoryIn most computers there are a variety

of memory technologies that are used to store specific types of information. The two main types are

Random Access Memory (RAM) Read-only Memory (ROM)

Random Access Random Access MemoryMemory

Information can be both read from or written to RAM. This type of memory stores the instructions and data of a currently executing program.

The problem with RAM is that it is volatile i.e. its contents are erased as soon as the computer is switched off.

Additionally RAM is a finite resource (also expensive) and therefore limited. The amount of RAM usually determines the size of the programs that can be executed and the size of the data they work on.

Read-Only MemoryRead-Only Memory ROM’s contain information that are ROM’s contain information that are

read-onlyread-only i.e. i.e. their contents can only their contents can only be readbe read..

The contents of ROM’s are The contents of ROM’s are non-non-volatilevolatile i.e. they are not lost after the i.e. they are not lost after the machine is switched off. machine is switched off.

ROM’s tend to store programs that are ROM’s tend to store programs that are required to boot-up your computer. required to boot-up your computer. These programs These programs load the operating load the operating systemsystem as well as execute a set of test as well as execute a set of test routines called the routines called the POSTPOST ( ( Power On Power On Self TestSelf Test ). ).

Hardware ( Memory )Hardware ( Memory )

CPU

Main Memory

Device Driver

Secondary

Storage Device

Simplified Memory Access Diagram