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