Memory Systems
- Created by: horme0520
- Created on: 05-02-20 13:45
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- Memory
- RAM
- Random Access Memory
- Computer stores data and instructions for the short term
- Used while other instructions are being carried out
- Volatile
- Anything on it will disappear when the power is cut
- ROM
- Read Only Memory
- Where instructions and data are stored don't need to be changed during normal use
- Non-volatile
- Data is still stored after the power is cut
- Cache
- Very fast memory
- Usually stored within the processor
- Stored while instructions are being carried out in the processor
- Bigger caches are split into smaller sections to carry out instructions faster
- Usually include layers
- Goes from RAM to CPU with levels in between
- Hard disc drives
- Can store large amounts - up to 1TB
- Disc spins and read-write heads move across them
- Encoded as opposing magnetic polarities on the surface of the disc by electromagnets in the read-write heads
- Stacks of non-removable discs coated in magnetic material
- Moving components can break
- Very reliable
- Strong magnets could erase the data
- Qualities
- 500MB
- Cheap
- Internal devices are fixed, external hard discs are portable
- Reasonably durable but can be damaged if dropped or knocked
- Generally reliable if looked after
- Long-term storage of instructions and data
- Optical storage
- Compact discs (CDs) can store up to 700MB
- Digital versatile discs (DVDs) can store up to 4.7GB
- Blu-ray discs can store up to 50GB
- Single spiral track running 5km from the inside to the outside
- Data stored by etching pits into the track
- Light hits land = reflected back to a detector (1)
- Light hits pit = shattered away (0)
- Discs covered in a translucent dye
- Light passes through and is reflected by disc surface
- Powerful laser burns the dye and creates black spots
- Reflective areas = 1, black spots = 0
- Susceptible to scratches and shattering
- Solid-state memory
- Made from NAND flash memory
- Stored as an electrical charge in the silicon
- Non-volatile
- Can electrically erase and reprogram it
- All transistors are charged (set to 1)
- Save operation begins = current is blocked and switched to 0
- RAM
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