Storage Flashcards
What are the two types of memory used in computers?
- RAM, Random Access Memory
* ROM, Read only memory
What is stored in RAM?
- Programs and data that are currently being used.
* Operating System
What does it mean for RAM to be volatile?
Contents are lost when the computer is switched off.
What is ROM used for?
• Holding information that needs to be permanently in memory.
What kind of information is stored in ROM?
Computing boot-up instructions.
What does it mean for ROM to be non volatile?
Contents of ROM are retained when the computer is switched off.
Where does the computer store running programs and data?
RAM
Where are programs and data copied from into RAM?
• Copied into RAM from a source of secondary storage, e.g. a hard disk drive.When do you
What is virtual memory?
A part of the hard drive used an as extension to RAM.
When may virtual memory be used?
When the computers RAM is not large enough to store all the programs simultaneously.
What are some disadvantages to virtual memory?
- Can cause disk thrashing
* Slower than RAM memory.
What is primary storage?
Volatile storage
What is a computers primary storage?
RAM
What is an advantage of storing data on secondary storage?
It is non volatile, and it contains its contents when the computer’s power is turned off.
What are some disadvantages of secondary storage?
- Not directly accessible to the processor
* Slower access speeds.
What are some advantages to solid state media?
- More durable
- Faster than hard disk drives
- Consumes less power
- More portable
How do optical disks work?
- Using a high powered laser to burn sections on its surface, making them less reflective.
- A laser at a lower power is used to read the disk by shining a light onto the surface and a sensor is used to measure the amount of light that is reflected back
- A CD ROM disk has pits in its surface, and areas without pits known as lands.
- At the point where a pit starts or ends light is scattered and not reflected back so well.
- Reflective and non reflective areas are read as 1s and 0s, and used by the computer.
How do recordable disks work?
They use a reflective layer with a transparent dye coating that becomes less reflective where a laser burns a spot in the track.
How do rewrite-able disks work?
- Use a laser and a magnet in order to heat a spot on the disk and then set its state to become a 0 or a 1 using the magnet before it cools again.
- A DCVD RW uses a phase change alloy that can change between amorphous and crystalline states by changing the power of the laser beam.
What is an advantage of optical storage?
- Cheap and to produce.
* Easy to send through the post for distribution purposes.
What are some disadvantages of optical storage?
• Easy to become corrupted through excessive sunlight or scratches.
How does solid state memory work?
- Comprised of millions of NAND flash memory cells.
- Feature a controller that manages pages and blocks of memory.;
- Each cell works by delivering a current along the bit and word lines to active the flow of electrons from the source towards the drain.
- Current on the word line is strong enough to force a few electrons across an insulated oxide layer into a floating gate.
- Once the current is turned off, these electrons are trapped, state of the NAND cell is determined by measuring charge in the floating gate.
- No charge is considered a 0, and charge is considered a 1.
What are the different optical disk formats?
- Ready Only
- Recordable
- Re writable formats.
How does a hard disk work?
- Uses rotating platters coated with magnetic material.
- Ferrous particles on the disk are polarised to become either a north or south state, representing 0 or 1.
- Disk is divided into tracks in concentric circles, each track is subdivided.into sectors
- Disk spins very quickly at speeds of up to 10,000 RPM.
