3.5 Memory and storage Flashcards
What are the 3 types of storage a computer has?
- Primary Storage
- Secondary Storage
- Off-line storage
What does RAM do?
- Primary Storage
- Can be written to or read from
- Data is only stored temporarily, and all memory is erased without power, it is volatile
What is an ‘embedded computer’?
- A computer built into another device to carry out one or more specialised tasks
- eg. a calculator
- Has not much RAM (few KB)
What is a ‘general purpose computer’?
- The modern form of computer
- eg. Desktop PC, smart phone
- Generally has a few GB of RAM
What is ‘ROM’?
- Read Only Memory
- It does not loose its data when it looses power
- The ROM holds data that is used to control the device before the system software on start up
What is firmware?
ROM that holds programs that run on an embedded computer
What does ‘bootstrap’ mean?
ROM that contain start up instructions for the computer
What is ‘EPROM’?
- Erasable Programable Read Only Memory
- ROM that can be erased and re written
What is flashing?
The process or erasing and rewriting the programs on ROM
Primary storage…
- Directly accessible by the processor
- Temporarily stores data
- Can be read from and written to extremely quickly
- Normally a few GB capacity
- Fixed within the computer
Secondary storage…
- Not directly accessible from the processor, data first has to be transferred into RAM
- Data is permanently stored until it is erased
- Slower to read and write to than primary storage
- Can be up to a terabyte or more in capacity
- Some secondary storage devices are removable
What are the 3 types of secondary storage?
- Magnetic
- Optical
- Solid-state
What is magnetic storage?
- Read, write and erase data using electromagnets
- The storage is usually a hard disk or tape with small magnetic dots that can be charged either positively or negatively using electromagnets, this is binary data
- Tape based storage use a cartridge of looped magnetic tape that passes over an electro magnet to read/write/erase data, however data is stored serially and isn’t good for saving files to
Explain how disk based magnetic storage works…
- There are several disks called platters
- The platters can be made from metal or glass
- They have a magnetised coating on which the data is stored
- Dots lie in the tracks that run around each platter
- All platters are on a spindle
- Spindle rotates at high speed
- The dots pass under a moving electromagnetic arm
- The arm moves back and forth across the platters to access data from different tracks
What is the ‘data transfer rate’?
The speed at which data can be moved to and from a storage device
Explain how optical storage works…
- Shines a laser onto plastic disks
- The disks have an aluminium coating to make them reflective
- The surface of the disk has one large track the spirals out from the centre
- Data is stored on the track using a laser to make PITS and the are between the pits is called LAND, these to areas reflect light back differently are represent the binary
- The number 11101001 would be pit;pit;pit;land;pit;land;land;pit
- They have a good data transfer speed
CD and DVD acronyms…
Compact Disk
Digital Versatile Disks
DVD’s use a higher frequency laser than CD’s and mean that the land and pits can be closer together and smaller on a DVD meaning more data can be stored on a disk of the same physical size.
CD capacity
700MB
DVD Single Layer capacity
4.7GB
DVD Dual Layer capacity
9.4GB
Blu-ray Single Layer capacity
25GB
Blu-ray Dual Layer capacity
50GB
Blu-ray Triple Layer capacity
100GB
Blu-ray Quadruple Layer capacity
128GB
Difference between R and RW with optical disks?
R:
- Comes empty
- Can be written to once
- Data can be read multiple times
RW:
- Can be written to and read from repeatedly
- High power lasers can be used to make the surface flow and fill the pits, effectively wiping the disk and allowing it to be written to again
What is ‘solid state’ storage?
- No moving parts
- Very very fast read and write speeds
- Uses flash memory
- Physically small
- 230 Megabytes per second
- Up to 4TB
- More expensive to produce than magnetic and optical equivalents
- Uses low power
- Ideal for portable/handheld devices
5 factors in deciding which type of secondary storage device is required….
- Capacity
- Transfer speeds
- Portability
- Durability
- Cost
