memoryMore technically referred to as Primary Storage

Computer Storage• Computers have two kinds of storage:

• Primary Storage• Secondary Storage

• Primary storage is also called memory.• Secondary storage is often called storage.• Individuals often do not distinguish between these two

types of computer storage.

Primary Storage• Connected to the motherboard and is the place where

programs and data are kept while they are being used.• The ENIAC was one of the first computers, built for

computing artillery trajectories during WWII.• In order to change its program, the machine would have

to be rewired.• John von Neumann, one of the mathematicians on the

ENIAC project came up with the idea that a program should be stored in the computer’s memory while it was running.

• All modern computers use von Neumann architecture.

Secondary Storage• The place where programs and data are kept when not in

use.• Secondary storage is typically implemented as hard disks,

CD/DVD, SSD, and flash “memory”

Memory Implementation• On modern computers (almost any computer from the

past 20 years or so) memory is composed of semi-conductor chips. There are several kinds.

• RAM (random access memory)• Dynamic RAM• Static RAM

• ROM (read only memory)• There are other types which we shall conveniently ignore

which combine the two characteristics.

RAM• RAM is volatile meaning that when power is lost the

contents of RAM are erased.• RAM is therefore not suitable for long term storage of

stuff.• RAM can be manipulated while the computer is running.• The contents of a RAM cell can be determined by the

computer using a process that is referred to as reading• The contents of a RAM cell can be changed by the

computer using a process that is referred to as writing.• When a memory location is written to, its former contents

are lost

RAM (continued)• When a memory cell is read, that particular cell cannot be

read again for a while.• When a memory cell is written, that particular cell cannot

be written again for a while.• Both of these “whiles” are very short times in the order of

10/1000000 or 100/1000000 of a second.• We refer to these mandatory rest times as the speed of

the memory.• In general if you use memory in a computer that’s too fast,

that will not hurt although it might actually slow it down under certain circumstances.

Static and Dynamic RAM• Static RAM is much faster than dynamic ram but also

much more expensive.• Dynamic RAM is typically much much larger than static

ram. • A typical static RAM module is less than 10 million cells in size. • Typical dynamic RAM modules range from about 250 million to 4

billion cells each.

• Static RAM is typically built into the processor and cannot be purchased separately.

• There are numerous types of dynamic RAM modules and are generally not interchageable

ROM• Read Only Memory is similar to RAM except that its

contents are not erased when the power is interrupted. • What is in the ROM stays in the ROM.• This is useful for things that will never change.• It is mandatory for stuff that has to be there when the

computer is turned on, such as instructions that tell it how to start.