Primary and Secondary Storage

Module G05c

Why do computers need memory?
Primary Storage = MEMORY

Two kinds of memory are most common

Secondary, or "Auxiliary" Storage

Why do computers need secondary storage?
Common types of storage

Audience and Objectives

About this document...

Why do computers need memory?

Memory is the computer's working storage: it serves as its work table or desk.

Storing instructions: The fastest CPUs depend on getting instructions fast
Storing information: The only direct way to make changes
Working space: This is like the desktop of an office worker. It is necessary for spreading out books and papers while working on them.

Primary Storage = MEMORY

Fastest way to get information to the CPU: On a simple microcomputer: about 233,000,000 characters, or about 60,000 pages of typing, to the CPU each second (for a 233 mHz Pentium-based computer)
Volatile: = "evaporates quickly:" Primary storage can disappear quickly: loss of electricity, making mistakes, or just changing

Two kinds of memory are most common:

RAM: Random Access Memory

"Ordinary" memory used in all modern computers
Easy to read and write
Random Access: all parts equally close
Takes no longer to read one part than another part

ROM: Read Only Memory

Information stored at the factory; it can't be changed
Used for:

Startup instructions on almost all computers
Built-in programs on laptops, palmtops, and dedicated word processors
Game cartridges for Nintendo, Sega, etc.
Disadvantage: when you want to change it, you have to throw away the old chips or cartridges

Can also be accessed "at random"

Secondary, or "Auxiliary" Storage

It's not so swift, but longer-lasting:

Floppy disk to memory on a PC: about 50,000 characters per second
Hard disk to memory PC: about 33,300,000 characters per second
Lasts as long as you need it

Why do computers need secondary storage?

So they can "rest" (turn power off) without permanent loss
So they can "think of something else"
It's like the bookshelves or filing cabinets in an office: they're needed to store information in an orderly way while you work on something else, or while you go away for the weekend.

Common types of storage:

Diskettes: can be removed from the computer

3.5 inch diskette [Diskette drive courtesy of Teac®]
5.25 inch "floppy" disk (no longer common)

Hard disk or Hard drive (same thing) (This picture shows what they look like inside.) [Hard drive courtesy of Seagate®]

Available in several sizes (1 Gb, 2 Gb, 4 Gb etc.)
Permanently enclosed in their drive mechanism

CD-ROM [CD courtesy of Sony®]

Older standard stores up to 650 Mb
DVD stores up to 17 Gb
Most can only be read - needs special device (CD-R) to write - more expensive.

Audience:

This is for people beginning to learn about the parts of a computer. It is expected that you know the general organization of a computer, and the vocabulary associated with it (see modules G01c, G02c, and G04c)

Objectives

When you successfully complete this lesson, you will be able to demonstrate understanding of...

The concept of computer storage;
Primary storage, or "memory";
The primary characteristics of memory: speed and volatility;
Why computers need memory;
The main types of memory used now: ROM and RAM;
The uses of ROM and RAM;
Secondary, or "auxiliary" storage;
The characteristics of storage: less speed but more permanence;
Why computers need storage;
The most common types of storage used with computers now