Secondary Storage

Secondary storage (auxiliary storage) is all data storage that is not currently in a computer's primary storage or memory. This is a computer memory, which is held outside the CPU. It is non-volatile: it remains stable when the computer is turned off.

Magnetic Tape How it store data? – Magnetism(on plastic tape) Features – Sequential access – slow read-write access removable from the computer Main types – There are many sizes and types of tape, but tape is rarely used in modern computer systems.

Floppy Disk How it store data? – Magnetism(on circle of plastic) Features – Direct access – Read-write access removable – Low capacity Main types – Floppy disk are available in several sizes, but they have low storage capacity and rarely used in modern computers.

Hard disk How it store data? – Magnetism(on a stack of metal disks inside the computer case) Features – Direct access – Read-write access usually fixed in one machine – High capacity Main types – Hard disk are available in several sizes, they have high storage capacity and are commonly used in modern computers.

Optical Disk How it store data? – Microscopic pits burned into a smooth surface by a laser. They are invisible to normal vision. Features – Direct access – Read-Only, access unless you have the software to ‘burn’ new data on to the disk – removable – High capacity Main types – CD’s are used to store music and large data files. DVD’s have even higher capacity and are used to store very large amount of data such as a movie.

Flash Memory How it store data? – Microscopic silicon circuits Features – Direct access – Read – write access – Removable – High capacity Main types – Flash memory can be packaged in a number of ways, in sticks or cards, which can be plugged into a computer with a suitable socket.

Access Computer access to storage means that there is a flow of data between the CPU and storage.

Sequential Access This means the stored data can only be accessed in order. A video tape is an example of sequential access. Access is slow.

Direct Access This means any part of the storage can be accessed right away. A DVD is an example of direct access.

Capacity The capacity of storage means how much data it can hold.

Access Speed This is how quickly the processor can read data from storage.

Hard drive This is a stack of metal disk, which is fixed inside the main computer case. It can store a lot of data but you can only access the data if you use the computer where it is stored. External hard drives can be bought. The Surface of a hard disk is divided into tracks and sectors.

Interface The connection between any two systems or parts, which allows them to communicate. Secondary Storage is connected to the processor via an interface. An interface typically include a port and a buffer.

Some common interface standards include: SCSI(Small Computer System Interface) IDE(Integrated Drive Electronic) SATA(Serial Advanced Technology Attachment) Firewire USB(Universal Serial Bus)

Activity Investigate at least three types of storage, and write a short paragraph or report on each of them. What are the meaning for each of the following: – CD-ROM – CD-R – CD-RW – DVD-R – DVD-RW