Components of a computer and their uses Flashcards
1
Q
Registers
A
Registers are small storage locations used to hold data temporarily. They have high read and write speeds.
2
Q
Current Instruction Register
A
Holds the current instruction that is being executed, divided into operand and opcode.
3
Q
Memory Data Register
A
Stores the data which is to be sent or fetched from memory
4
Q
Memory Address Register
A
Stores the address of instructions and data that need to fetched from or sent to memory
5
Q
Opcode
A
The actual instruction
6
Q
Operand
A
the data the instruction applies to
7
Q
Program Counter
A
stores the memory address of the next instruction.
it is incremented after an instruction has been read from memory and interpreted
8
Q
Arithmetic Logic Unit
A
completes all the arithmetic (addition and subtraction) and logical operations (including AND, NOT, OR and XOR) as well as binary shifts
9
Q
Control Unit
A
Control unit is a register in the CPU that controls and coordinates the activity of the CPU.
Control signals are sent along the control bus between the control unit and the other components of the computer.
10
Q
Jobs of the control unit
A
- Controlling and coordinating the activities of the CPU
- Managing the flow of data between the CPU and other devices
- Accepting the next instruction
- Decoding instructions
- Storing the resulting data back in memory
11
Q
Address Bus
A
A one directional bus
It transmits memory addresses specifying where data is to be sent to or retrieved from in memory
12
Q
Bottleneck address bus
A
the width of the address bus determines the maximum possible capacity of the system
13
Q
Address bus average width
A
32 bits
14
Q
What does the width of the address bus determine?
A
the max possible memory addresses of the system
15
Q
Data Bus
A
A bi-directional bus for moving data and instructions between system components
16
Q
Buses
A
the communication channel between the CPU, the memory and other components
17
Q
System bus
A
Address Bus, Data Bus and Control Bus
18
Q
Bottleneck Data Bus
A
A wider bus can transmit larger values/more bits per instruction
19
Q
Data bus width
A
same as the computers word size
20
Q
Control Bus
A
A bi-directional bus used to transmit control signals between internal and external components.
It coordinates the use of the buses (data and address).
It provides the status info between system components.
21
Q
Width of the bus
A
is the number of parallel wires the bus has
22
Q
The number of parallel wires the bus has
A
is the number of bits that can be transferred simultaneously
23
Q
Control Signals
A
- memory read
- memory write
- bus request
- bus grant
- clock signal
- interrupt
24
Q
Interrupt
A
A device sends a signal on the control bus to show the CPU it needs attention
25
Memory read signal
causes data from the addressed location in RAM to be placed on the data bus
26
Memory write signal
causes data on the data bus to be written into the addressed location in memory
27
Clock signal
Used to synchronise operations
28
Bus grant signal
Indicates that the CPU has granted access to the data bus
29
Bus request signal
indicates that the device is requesting the use of the data bus
30
Fetch-decode-execute cycle
1. Load the address in PC into MAR
2. Increment the PC by 1 (using ALU)
3. Load instruction given by memory address in the MAR into MDR - done via the data bus
4. Load instruction in MDR into CIR
5. Decode instruction in CIR by splitting into operand and opcode
6. Execute instruction
7. Cycle repeats itself
31
Factors affecting the CPU performance
number of cores
cache
clock speed
32
clock speed
indicates the number of instructions the CPU can process per second
33
clock speed units
hertz (one cycle per second)
34
clock
a device that generates a timing signal that changes at a regular frequency.
It is used to synchronise communication between the components of the CPU and the rest of the system
35
Pros of increasing clock speed
can carry out more instructions in a given time - which increases performance
36
Cons of increasing clock speed
- requires more energy, which increases costs
- more energy = more heat is generated, so the computer must be cooled by cooling systems
37
Multiple cores
mean multiple CPUs are working on a single computer, which means the processor can perform more than one fetch-decode-execute cycle
38
Pros of multiple cores
It may speed up processing
39
Why may additional cores be redundant?
- if the software is only written for one core
- if the output of one operation is required to perform the second operation
40
Cons of multiple cores
- multiple cores = more materials needed, which increases costs
- multiple cores = more energy/power needed, which increases costs and generates more heat, so need greater cooling systems
- has a more complicated circuitry
- doesn't always improve performance
41
Cache memory
Special high-speed memory used by a computer. Stores frequently used instructions and data
42
Why is cache memory better than RAM?
cache operates faster ---> than main memory ---> as data is transferred ---> in + out of cache memory ---> more quickly ---> as it is closer to the CPU ----> which makes CPU more efficient ---> as less time is spent ---> waiting for data ---> to be transferred
43
Pros of cache
- less time spent fetching data, which improves performance
44
Cons of cache
expensive
45
What happens when cache is used up?
unused instructions are replaced
46
Pipelining
Involves fetching one instruction, whilst the one before is decoded, and the one before that is executed
47
Pros of pipelining
improves the efficiency of CPU, because it can process more instructions simultaneously, while reducing the delay between completed instructions
48
Cons of pipelining
only useful if you can predict subsequent instructions. If the wrong instruction is fetched (ie due to a jump) it has to be thrown away, wasting time
49
Contemporary Processor Architecture
Incorporate aspects of Harvard and Von Neumann's architecture.
- same memory is used for both instructions and data
- cache is divided into instruction and data
- there are multiple parallel data buses
50
Harvard architecture
- instructions and data are stored in separate memory units
- separate set of system buses for both instructions and data
51
Pros of Harvard architecture
- can simultaneously store data whilst fetching instructions, making it faster
- memory units can be different sizes, which can make more efficient use of space
52
Cons of Harvard architecture
- is more expensive as requires more RAM
53
Von Neumann architecture
- a shared memory for both data and instructions
- shared buses between data and instructions
54
Pros of Von Neumann architecture
- programs can be optimised in size
- cheaper to develop, as the control unit is easier to design
55
Cons of Von Neumann architecture
- Von Neumann bottleneck
56
Store instruction
STA
57
End instruction
HLT
58
Branch if zero or +ve instruction
BRP
59
Branch always instruction
BRA
60
Output instruction
OUT
61
Load instruction
LDA
62
Add instruction
ADD
63
Subtract instruction
SUB
64
Branch if zero instruction
BRZ
65
Data location
DAT (put at the very end of code in the format of variable name, DAT, value)
66
Input instruction
INP
67
RISC
- reduced instruction set computing
- contains a small instruction set where each instruction is performed in one clock cycle
68
Uses of RISC
Smartphones and tablets using ARM processors
69
Pros of RISC
- simpler hardware
- single machine cycle per instruction
- smaller in size as less complex circuitry, so less silicon, so cheaper to produce
- lower energy requirements as smaller, so less heat
- smaller number of simple, standardised instructions that are of a fixed length
- can support pipelining*
70
Cons of RISC
- fewer addressing modes available
- heavy use of RAM
- lower clock speed - not good for complex tasks with large code sizes
- as the emphasis is on the software, the compiler has to do more work
71
Why do RISC processors result in increased battery life?
- smaller instruction set
- fewer transistors/ less complex circuitry
- less power required
72
CISC
- complex instruction set computing
- large number of instructions each taking multiple machine cycles to carry out
73
Uses of CISC
laptops or desktop computers
74
Pros of CISC
- emphasis is on the hardware, so compiler has to do less work (compiles faster)
- makes more efficient use of RAM than RIC
- multiple addressing modes available
- has higher clock speeds, as has smaller code sizes, as typically an instruction to carry out the process
- large number of complex instructions of variable length
75
Cons of CISC
- has more complex hardware
- physically larger, due to more complex circuitry, so requires more silicon to make, so more expensive
- greater energy consumption = more heat = greater cooling needed
- multiple clock cycles per instruction
- can't make use of pipelining*
76
MIMD
- multiple instructions multiple data
- multiple instructions carried out on multiple data using multiple cores
77
SIMD
- single instruction multiple data
- a single processor carries out a single instruction on multiple pieces of data (parallel processing)
78
GPU
- graphics processing unit
- used for rendering graphics and processing many parallel streams of data simulatenously
79
CPU vs GPU
- CPU excels at complex instructions for a small data set
- GPU excels at simple instructions for a large data set
80
GPU uses
machine learning (AI), graphics, gaming, data analysis, oil exploration, weather analysis
81
INPUT devices
keyboard
mice
microphone
webcamera
barcode scanner
card reader
82
OUTPUT devices
speaker
printer
monitor
projector
83
example of input and output device
touch screen
games controller
84
what is an input device?
gathers data on the outside world and places it into a computer system
85
what is an output device?
takes data which is stored in a digital form and converts it into another form we can process (ie sound, images or vibrations)
86
what is a storage device?
any device that is used for either temporary or permanent storage of data - can be internal or external
87
STORAGE devices
SD card
Blu-ray
DVD
CD
USB/flash drive
magnetic hard drive
portable SSD
cloud storage
88
3 types of secondary storage devices
magnetic
optical
solid-state/flash
89
Optical storage
- data is written to the surface of a reflective disk using pits (depressions) and lands.
- a laser beam passes over the surface of a land, and the light beam reflected back is interpreted as a binary value
90
Pros of optical storage
- cheap
- highly portable + lightweight (so easy to post or carry)
91
Cons of optical storage
- surface of disk degrades over time with exposure to sunlight
- scratches can corrupt data
- low capacity
- slow access speeds
92
magnetic storage examples
magnetic tape, floppy disk hard disk drives
93
magnetic storage
- where metal disks called platters are magnetised
- a read-write head moves over the surface of the platter and is able to detect and modify the magnetic properties of the platter
94
Pros of magnetic storage
- cheaper than SSDs
- high capacity
95
Cons of magnetic storage
- can be affected by magnetic fields and heat (so may require expensive cooling systems)
- slower than SSDs (as they contain moving parts)
- less durable (as will eventually fail due to moving parts)
- not robust if dropped (due to moving parts)
96
solid state storage
uses flash memory so data is read and written directly to blocks and pages on the silicon micro-chips
97
examples of solid-state storage
- USB pens
- SD cards
- SSDs
98
Pros of solid state
- durable (have no moving parts)
- robust if dropped (due to no moving parts)
- portable and take up very little space (due to lack of moving parts) reducing physical device size
- fast access times
- high capacity
99
Cons of solid state
- expensive
- limited lifespan (as limited number of read/write cycles)
100
Why do we need secondary storage?
- It is a non-volatile, long-term form of storage
- it is used to keep programs and data indefinitely (otherwise all our files and apps would be lost when the power is switched off)
101
Forms of primary storage
RAM
ROM
cache memory
102
RAM
fast, read-write, volatile memory that stores the data and programs that the computer needs whilst in operation or is using (e.g. OS)
103
ROM
- non-volatile, read-only memory embedded into the motherboard of a computer
- used to hold the bootstrap and BIOS of the computer
104
Virtual memory
- when a small section of the hard disk is reserved to act like RAM
- when the program in virtual memory is needed, it is swapped with something else in RAM
105
Explain why getting more RAM would be preferable to using virtual memory?
- access to data in RAM ---> faster than having to swap ---> programs in + out of RAM ---> before accessing them
- constantly swapping ---> programs + data ---> between RAM + the hard disk ---> can cause disk thrashing ---> takes time + decreases performance
- reading data ---> from a hard disk ---> is slower than ---> from RAM
106
Virtual storage (cloud)
when data is stored over the internet in the cloud rather than in a local storage device
107
Examples of virtual storage
DropBox, OneDrive, Google Drive
108
Process to get to CLOUD
RAID ---> NAS ---> SAN ---> CLOUD
109
NAS
- network accessed storage
- contains multiple hard drives in a RAID configuration (to create backups of your data)
110
Uses of NAS
as a home server (to share files, videos etc)
111
Pros of NAS drivers
- built for 24/7 action
- cheaper than a PC drive
- heat resistant
- can serve the data needs of multiple people on a network simultaneously
112
SAN
is multiple NAS drivers
113
Pros of CLOUD
- Flexible storage is offered ---> can increase when needed
- You do not need to ---> purchase or maintain ---> expensive hardware
- The Cloud storage provider ---> is responsible for the security ---> of your data + regular backups
- One cloud storage centre ---> is more environmentally friendly ---> than millions of individual servers
- You do not need ---> networking skills or maintenance workers
- Easy to share files between devices
113
What is cloud?
involves renting someone else's SAN
114
Cons of CLOUD
- Need a reliable Internet connection ---> to access servers
- Have no direct control ---> over the security ---> of your data
- Keeping your data ---> on another company's server ---> may cause issues of ownership
- You may be responsible ---> for any data security breaches ---> even if you have no direct control ---> over the security of your data
- Subscription fees ---> may be expensive
