Storage media Flashcards
Three types of storage
- primary storage
- secondary storage
- off-line storage
Primary storage
Computer’s internal storage. Storage where the data are held ready for processing. The capacity is quite small. Separated into RAM and ROM.
RAM
Random access memory. Is volatile chip. Used in normal operations after starting up and loading the operating system.
ROM
Read only memory. Is non-volatile chip. Used to start up and loading the operating system.
EPROM
Erasable programmable read-only memory
Can be erased by UV light and than rewritten with a process that needs higher than usual voltage applied.
EEPROM
Electrically erasable programmable read-only memory
Allows entire content to be electrically erased and then rewritten electrically, so it doesn’t need to be removed form computer.
Volatile
Requires constant source of power. If power is lost, data on a chip will be lost also.
Non-volatile
Doesn’t require a constant source of power. When power is lost, a chip will keep all information stored.
Secondary storage
Software and data also need to be kept for future use. They can be held in secondary storage, until they are erased or rewritten.
The CPU in a computer can only access data when…
it is being held in the RAM. So programs, data and operating system must first be transferred into RAM from secondary storage.
Key features of primary storage
- directly accessible by the processor
- temporarily stores data
- fixed within a computer
- can be read or rewritten instantly
Key features secondary storage
- data first has to be transferred into RAM
- permanently stores data till erased
- slower to read data and write them
- large storage
- some devices are removable
Three types of secondary storage
- magnetic
- optical
- solid-state storage
Magnetic storage
Read, write and erase data by using electromagnets and magnetic fields to control tiny magnetic dots of data. Either tape based or disk based.
Disk-based magnetic storage
Consists of several disks known as platters. It can be made from metal or glass. They have magnetised coating on which the data dots are stored. The platters are spinning an the data are read or written, by heads.
Optical storage
Read data by shining a laser beam onto the surface of plastic disks. Coated with aluminium to make them reflective. Data is written by using a laser to make pits.
Pit
An indention on the surface of an optical disk, used to represent data.
Land
The raised surface on the surface between pits on an optical disk.
Burning
The process of recording data onto an optical disk. Laser burns the pits into the disk surface.
Blu-ray disk
Use a blue-violet laser that operates at a shorter wavelength. This gives more precision when writing or reading the disk. The data can be packed even closer together than DVD.
Compact disk (CD)
An early, but still used, optical medium.
Digital versatile disk (DVD)
A later, higher capacity optical medium. Use higher frequency laser, this allows the pits to be packed tightly, so more data can be stored.
Blue-ray and DVD can have more…
than one reflective layer on which data can be stored.
Types of optical media:
- ROM
- R
- RW
ROM optical media
Read only. The data is already burned onto the disk by a manufacture or other user. Can be only read.
-R optical media
The disk is initially empty of data. The data can be written only once. Once written a data can be only read.
-RW optical media
The disk is initially empty of data. It can be written to and read from repeatedly. This disk has a reflective surface that have pits burned in. By using a higher power laser, the pits can be erased, which returns the disk to a blank state.
Solid-state storage (SSD)
Has no moving parts. Instead, high speed flash memory is used to store data.
Examples of SSD
USB RAM sticks
Solid-state hard drives
SD card
Solid-state cars used to store and transfer data.
Tre performance of solid-state devices
They are quite small in size, but their data transfer rate is much quicker than other types of storage. Can be written to and read from many times.
Uses of SSD
- physically small size, makes them useful as portable storage device
- can be rewritten many times
Off-line storage
Any non-volatile storage device that is disconnected or removed from computer. E.g. USB, DVD, CD….
Factors when choosing an appropriate secondary device:
- capacity
- transfer speed
- portability-how easily the medium can be transported
- durability-how resistant the medium is to data loss and damage
- cost
