[Unit 1.1] Components of a computer Flashcards
Computer Systems
define main memory
storage locations that are directly accessible by CPU. faster but lower capacity than secondary storage
more expensive than secondary storage (per GB)
define secondary storage
storage the computer can store all data not used but needed in long term
what is RAM
Random access memory, where programs being run are temporarily stored:a
OS, programs, data running
Volatile (lost when power shuts off)
directly accessible by CPU
what is ROM
Read only memory.
can be read from but not written to
non volatile
smaller capacity than RAM
stores firmware/software rarely changed:
-BIOS, embedded systems.
what is flash memory
non volatile memory that can be changed to update BIOS
counts as ROM
what does the BIOS do
initialises hardware and boots up computer
loads OS from secondary storage to RAM
what is virtual memory
use of secondary storage as RAM by OS
how does virtual memory work
memory split by OS into pages
less used pages move into VM
when pages in VM are needed they can be swapped back into RAM
this is a slow process
what are the disadvantages of virtual memory
if it is used all the time the computer will pause when switching between apps.
this is called thrashing.
it lowers the life expectancy of SSD.
what is parallel processing
simultaneous processing of data
what are the four ways of achieving parallel processing
pipelining
GPUs
Multicores processing
distributed computing
how does pipelining achieve parallel processing. what are the disadvantages
Fetch decode and execute at the same time
increases instructions processed in given time
complicated to build
branching instructions degrade performance
how does multicore processing achieve parallel processing
2 or more independent processing units
each core executes instructions independently
-each core does its own pipelining
how does a GPU achieve parallel processing
it is a specialised processor to perform graphical calculations
allowing main CPU to perform other tasks
perform same calc to multiple data at same time
has thousands of cores
has its own ram
how does distributed computing achieve parallel processing
multiple computers work across a network to solve a common problem
what are the limitations of parallel processing
task interdependency (not all tasks can be parallelised)
scalability constraints
specialised software (multiple cores has to be coded to be used)
amdahls law (performance limited by parts of problem that cant be parallelised)
what are the advantages of parallel processing
faster for handling large amounts of data
not limited by von neumann bottleneck
is using maximum power of CPU
what is a CISC design for the CPU
Complex Instruction Set Computer
has a large instruction set built in
-hardware more complicated but software easier
single instruction may take many clock cycles
allows for powerful instructions at cost of slower and larger CPU
Desktops
what are the advantages of a CISC design for the CPU
simplifies programming
easier for compilers
easier for low level programmers
shorter programs
what are the disadvantages of a CISC design for the CPU
more hardware needed
more transistors
larger in size
more expensive
consumes more power
what is a RISC design for the CPU
Reduced Instruction Set Computer
has small highly optimised instruction set built in
-simpler hardware, harder software
complex instructions arent used frequently
each instruction carried out in 1 cycle of FDE
Phones and embedded systems
what are the advantages of a RISC design for a CPU
less transistors
easier to design
smaller in size
more power efficient
cheaper
pipelining can be implemented easier
what are the disadvantages of a RISC design for a CPU
more software for complex tasks
longer programs
large number of general purpose registers needed
what other uses do GPUs have
cryptomining
AI and ML
scientific simulations
modelling
editing
gaming
data analysis
cryptography
VR and AR
What is Moore’s Law
The number of transistors on CPU double every 2 years (approx) from 1965
What are the 5 special purpose registers?
PC, CIR, MAR, MDR, ACC
What is the PC
stores the address of the next instruction to be fetched.
increments by 1 after each FDE cycle.
However, instructions can modify next address if it is elsewhere
What is the CIR
stores most recently fetched instruction, waiting to be decoded and executed.
What is the MAR
Stores the memory address of the instruction waiting to be fetched from memory
What is the MDR
Stores the data of the instruction which has just been fetched from memory
What is the ACC
stores the results from the ALU
What is the address bus
provides memory address to system memory or I/O devices
what is the data bus
transfers data between CPU and memory or I/O devices
What is the control bus
provides control signals that cause the memory or I/O devices to perform a read or write operation.
What is the use of general purpose registers
to hold intermediate results while working through a calculation or algorithm.
What happens during the fetch stage of the FDE cycle
1-PC copies address of next instruction into MAR
2-CU loads address to be used onto address bus
3-CU sends a read signal down the control bus
-causing RAM to place instruction asked for on data bus
4-Instruction on data bus loaded into MDR
5-MDR copies into CIR
6-PC incremented by one or jump instruction
What happens during the decode stage of the FDE cycle
CU examines instruction in CIR and decodes
(each CPU has own instruction set that defines decoder)
What happens during the execute stage of the FDE cycle
-instruction in CIR is carried out by CPU
-repeat FDE cycle with next instruction
what is clock speed
how quickly CPU can carry out FDE cycle
sends pulse at fixed intervals triggering next stage in FDE
what is cache
small amount of very fast memory built into CPU
(holds instructions frequently used)
what are the 3 levels of cache
L1 - smallest, fastest, expensive
L3 - largest, slowest, cheapest
what is the core (CPU)
a complete processing unit (CU,ALU,registers)
what are the benefits of having multiple cores in a cpu
more instructions can be carried out at same time
-multitasking
-parallel processing
what is parallel processing
splitting program between cores to execute faster
what is pipelining
technique of fetching an instruction while prior is being decoded and one before is being executed
-more operations happening in same amount of time
what are the issues with pipelining
sometimes programs branch (jumps to out of sequence instructions)
-cpu has to do “branch prediction”
-if an error is made the pipelines have to be flushed
what are the issues of having multiple cores in a CPU
programs have to be written to take advantage of the multiple cores.
What are the 5 components of the Von Neumann Architecture
-Memory (hold data and program)
-Control unit
-Input/Output devices
-ALU
-Bus
What are the 2 problems with the Von Neumann Architecture
1- cpu is faster than the bus
- Von Neumann Bottleneck
2- data and programs share memory
- can write data over instructions
Key features of Harvard architecture
-keeps data and programs separate in memory
-data and program have separate buses
-data and instructions can be fetched at same time
define storage devices
hold data and programs for long term
6 factors that you consider when choosing secondary storage
cost (per GB)
speed
capacity
durability
reliability
portablility
what are the three types of secondary storage
magnetic
flash/solid state
optical
how does magnetic storage work
magnetisable material represents a 0 or 1 depending on its polarised state (N or S)
(Dis)advantages of magnetic storage
Ad:
high capacity
cheap per GB
Dis:
vulnerable to magnetic fields, xrays and shock
not as reliable as others.
how does optical storage work
laser and sensor detects reflection to determine where pits are. represent 0s and 1s
(dis)advantages of optical storage
Ad:
cheap (for small amounts)
portable
reliable and durable
dis:
expensive (perGB)
slow read/write
computers no longer have disc drives
what are the different types of optical discs
CD-ROM: read only, 700MB
DVD-ROM: read only, 4.7GB
BluRay: read only, 25GB
CD/BluRay/DVD-R: recordable once
CD/BluRay/DVD-RW: rewritable multiple times
what is flash memory
a specific implementation of solid state memory that we use
what are the advantages of solid state memory
no moving parts
high read/write speeds
unaffected by shocks (robust)
lower power consumption
silent
portable
what the disadvantages of solid state memory
more expensive per GB
limited number of read/write cycles
Why cant SSDs be used for archiving files
with power the transistors charge are refreshed.
without power, charge dissipates
define input devices
peripherals used to provide data and control signals to a computer system
what are examples of input devices
keyboard
mouse
microphone
barcode reader
what are biometrics
identifying people using unique characteristics (e.g iris)
users must opt in and consent to the storage and processing of their personal data
what are examples of sensors
GPS, accelerometer, gyroscope, pedometer
what should be considered when choosing an input device
cost
speed
accuracy
reliability
define output devices
display result of processing data to the user
what are examples of output devices
monitors
printers
speakers
projectors
motors.
