Hardware Flashcards
(15 cards)
Describe primary memory
RAM- volatile.
Can hold program instructions and data
Programs to be executed are first loaded from backing store before being run.
Because RAM is much faster.
Operating system is held in RAM.
ROM- read only. Non volatile. Holds simple BIOS operating system burnt onto the chip at the time of manufacture.
BIOS runs a ‘bootstrap loader’ that looks for another operating system
Describe the central processing unit
controls the transmission of data to and from main memory. Processes the data in memory. Controls transfer of data between input, output and memory.
State the components of the cpu
control unit
Arithmetic logic unit
General purpose registers
Instruction sets
Memory address register
Memeory data register
Program counter
Current instruction register.
Describe MAR, MDR, PC and CIR
MAR- holds the address of the memory location currently being accessed.
MDR- holds the data read from or being written to memory
PC- the address of the next program instructions to be read from memory
CIR- the instruction most recently fetched from memory.
Describe buses
collections of wires inside the computer which transmit information between the components and also to input/output devices.
Describe the Address bus , data bus and Control bus
Address bus - used to specify the address in memory where data will be read from or written to
Data bus - used to transfer data from memory into the cpu or from CPU back to memory.
Control bus- used to send control signals between parts of the computer.
Describe RAM cache memory.
Cache is small, extremely fast memory.
Placed near or on the processor.
Stores regularly used data.
When full, least used is discarded.
Try to predict next instructions to be accessed and pre-fetch them into the cache.
Attempts to solve ‘von Neumann bottleneck’.
CPUs are so fast that data from ram can’t be fetched quickly enough to keep them occupied.
Describe disk cache
keeps copies of blocks of data in RAM do that recently accessed blocks can be read more quickly again from RAM rather than having to read from the slower hard disk.
Describe how cache works
data being read from RAM is copied into the cache- it records the address the data came from, the data itself and the timestamp when it was accessed.
CPU reads data from cache rather than ram.
Describe parallel processing
modern computers usually have mul;triple processors.
Code written to allow different lines of code to be carried out simultaneously across multiple processors.
Useful where large/complex calculations are being carried out.
-makes it run faster .
-programming more complex. Meaning benefits are rarely fulfilled.
Different parts of program run on their own thread.
-code only executed by one processor
What are external backing store
forms of non-volatile storage
Stores data to be used repeatedly
Usually slower and cheaper than RAM
Can sometimes be sued to backup data to keep it safe.
Describe mechanical storage
requires movement. E.g. hard disks and CD-ROM .
Slower access speeds but are also cheaper, in the case of hard disks they can have very large amount of storage.
Hard disks more likely to be damaged if dropped due to moving part.
Hard disks generally have a long life span.
Hard disks will sometimes require defragmentation.
CDROOM/DVD/BLURAY- small capacities.
Magnetic tape has large capacity. Still sometimes used for backup purposed because they are cheap and store a lot of data. Relatively fast when writing data but slow for recovering but can be easily stored in a safe or transferred for off-site backups.
Describe solid state drives
solid state and flash memory is faster but more expensive than hard disks.
Direct replacements for hard drives but use more expensive flash memory.
Less reliable over time but increasingly used in modern computers to improve speed
Made up if NAND flash- shock resistant.
No moving parts- power efficient.
Lighter, quieter, use less power, run cooler than hard drives
Don’t require defragmentation.
Compare memory and backing store speeds and cost
smallest size- RAM
Largest size- hard disks
Cheapest- flash memory
Most expensive- RAM and hard disks
Cost per Gb- RAM- 5.56. Hard disk- 0.03
Quickest read speed- RAM 10BG/sec
Slowest read speed- hard disks Cheapest- 100MB/sec
Describe disk fragmentation
