Chapter 8 Memory, Storage Devices and Media

ROM

read only, the data stored is already burned onto the disk by a manufacturer on another user, this data can only be read.

Capacity

the amount of data that can be stored within a medium

Land

the raised surface betweenthe pits on an optical disk

data transfer rate

the rate at which data is moved to and from a storage device

Offline Storage

Any non-volatile storage storage device or medium that can be disconnected (offline) or removed from a computer

Blu-ray

Capacity- 25GB single layer, 50GB dual-layer, 100GB triple-layer, 128GB quadruple layer Transfer speed- Portable- Yes Durability- Reflective surface is quite easily scratched, Disk is easily broken Cost per megabyte- Cheap for small volumes expensive for larger

DVD

Capacity-4.7GB single layer, 9.4GB dual layer Transfer speed- Medium up to 33MB per second Portable- Yes Durability- Reflective surface is quite easily scrached, Disk is easily broken Cost per megabyte- Cheap for small volumes expensive for larger

CD

Capacity-700MB Transfer speed- Slow up to 10MB per second Portable- Yes Durability- Reflective surface is quite easily scrached, Disk is easily broken Cost per megabyte- Cheap for small volumes expensive for larger

Magnetic Tape

Capacity-up to 185TB Transfer speed- Medium up tp 30MB per second Portable- Yes Durability-case is quite durable although tape can be eaily damaged Cost per megabyte- Extremely cheap

USB RAM Stick

Capacity-up to 1TB Transfer speed- Very quick up to 180MB per second Portable- Yes Durability- fairly durable but easily destroyed Cost per megabyte- Very cheap

Sd card

Capacity-up to 2TB Transfer speed- Medium up to 48MB per second Portable- Yes Durability- fairly durable but easily lost Cost per megabyte- Very cheap

Solid State Drive

Capacity-up to 4TB Transfer speed- Extremely quick up to 230MB per sec Portable- Yes Durability-Very durable, no moving parts Cost per megabyte- Expensive

Hard Disk Drive

Capacity-up to 8TB Transfer speed- fast up to 128MB per second Portable- Often fixed within a computer, portable versions exist Durability-very durable Cost per megabyte-very cheap

Disk based devices

Consists of several disks known as platters which can be made from metal or glass, they have magnetised coating on which the dots are stored. The dots lie in tracks that run around the platter. The platters are attached to a rotating spindle which spins the platters at high speed. Data is read written or erased as the dots pass under the read/write heads that sits on a moving arm. The arm moves back and forth across the platters to access data in different tracks.

RAM stick

Small solid state medium used to transport data

Solid state Storage

Solid state has no moving parts, instead a high speed flash memory is used to store data. Can be written to and read from many times, small in size but have a quicker transfer rate

Tape based devices

Tape based devices use a cartlige of looped magnetic tape, The magnetized data are stored in a series along the length of the tape, the tape passes over an electromagnetic read/write head, that reads writes or erases the magnetic dots

-RW

The disk is initially empty of data. It can be written to and read from repetedly. Can have pits burned into it by using a higher power laser, surface can be made to flow and cover the pits. Disk returns to blank state.

-R

The disk is initially empty of data. It can be written to only once. Once written data can be read.

Burning

The process of recording data onto optical disk, the laser burns pits into the surface

Transfer speed

The rate of which data can be transferred to and from a medium

SD card

a solid state card used to store and transfer data

Solid State Drive (SSD)

a solid state equivalent of a hard disk drive

Compact disk (CD)

an early, but still used, optical medium

Pits

an indentation on the surface of an optical disk, used to represent data

Optical Storage

optical storage devices read data by shining a laser beam onto the surface of plastic disks. The disks are coated with aluminium to make them reflective. The reflective surface is covered in one large track that spirals outwards outwards from the centre of the disk. Data is written on the track by using a laserto make indentations known as pits

Blu-ray disk

a modern, extremely high capacity optical medium

Portability

How easily a medium can be transpored from one location to another

Cost

How expensive the medium is (cost per megabyte or cost per gigabyte)

Durability

How resistant the medium is to data loss and damage from wear, tear and pressure

Primary Storage

-Directly accessible by the proccessor as it is internal to the computer -Temporarily stores data -Can be read from and written to primary storage almost instantly -Normally a few gigabytes in capacity -Fixed within thecomputer

Secondary Storage

-Not directly accessible to the processor-data first has to be transferred into RAM -Permanently stores data until erased -Slower to read data from and write data to, as it needs to be transferred into RAM first - Can be up to terabyte or more in capacity -Some devices are removable

Magnetic storage

Magnetic storage devices read, write and erase data by using electromagnets and magnetic fields to control tiny magnetic dots of data

Digitile Versetile disk (DVD)

a later high capacity optical medium