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OCR A Level Computer Science > 1.1 Systems Architecture > Flashcards

1.1 Systems Architecture Flashcards

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1
Q

What is the purpose of the control unit (CU)?

A
  • Co-ordinates all activities of the CPU
  • Directs the flow of data between the CPU and other devices
  • Accepts, decodes, executes and stores results back in memory
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2
Q

What is the purpose of the program counter (PC)?

A
  • Holds the address of the next instruction to be executed
  • e.g. the next instruction in a sequence of instructions or an address to jump to if the current instruction is a command to branch
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3
Q

What is the purpose of the memory address register (MAR)?

A
  • Holds the address of the memory location from which data or an instruction is to be fetched or to which data is to be written
  • Sends the address to memory down the address bus
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4
Q

What is the purpose of the memory data register (MDR)?

A
  • Used to temporarily store the data which is read from and written to memory
  • All data to and from memory must travel down the data bus and pass through the MDR
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5
Q

What is the purpose of the current instruction register (CIR)?

A
  • Holds the current instruction being executed
  • Contents of the MDR are copied if it’s an instruction
  • Contains the opcode and operand of the current instruction
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6
Q

What is the purpose of the arithmetic logic unit (ALU)?

A
  • Performs logical and arithmetic operations on data
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7
Q

What is the purpose of the accumulator?

A
  • Holds the results of calculations made in the ALU
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8
Q

What are buses?

A
  • A physical set of parallel wires connecting and carrying groups of bits between several components of a computer
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9
Q

What is an address bus?

A
  • Carries memory address which identify where data is read from or written to
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10
Q

What is a data bus?

A
  • Carries that binary that make up the actual information being transmitted around the CPU
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11
Q

What is a control bus?

A
  • Controls command and control signals to and from every other component of the CPU
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12
Q

What are the factors that affect the performance of the CPU?

A
  • Clock speed
  • Cache size
  • Number of cores
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13
Q

Factors that affect the performance of the CPU: clock speed

A
  • The number of instruction cycles it can execute per second
  • Measured in hertz
  • The faster the clock ticks, the more FDE cycles can be executed per second
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14
Q

Factors that affect the performance of the CPU: cache size

A
  • Holds data and instructions that are frequently accessed and used by the CPU
  • Much quicker to access than RAM
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15
Q

Factors that affect the performance of the CPU: number of cores

A
  • A complete copy of the CPU
  • CPUs with multiple cores have the power to run multiple programs at the same time
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16
Q

Why does doubling the number of cores not necessarily mean it will double the performance?

A
  • Extra communication is needed between the cores = extra time
  • Many programs are not designed to make use of multiple cores
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17
Q

What is pipelining?

A
  • The process of completing the FDE cycles of three separate instructions simultaneously
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18
Q

What is the instruction pipeline?

A
  • Consists of various stages an instruction must move through the processor
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19
Q

What is the arithmetic pipeline?

A
  • Parts of the arithmetic operation that can be broken down and overlapped as they are carried out
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20
Q

Von Neumann architecture (4)

A
  • Shared memory space for data and instructions (in the same format)
  • A single CU/processor follow a linear FDE cycle
  • One instruction at a time
  • Register used as fast access to data
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21
Q

Harvard architecture (4)

A
  • Instructions and data stored in separate memory units
  • Each has its own bus
  • Reading and writing can be done at the same time as fetching an instruction
  • Used by RISC processors
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22
Q

Contemporary Processor architecture

A
  • A modern computer architecture combining elements of both Von Neumann and Harvard architecture
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23
Q

What is the the purpose of Single Instruction Multiple Data (SIMD)?

A
  • Parallel processing is where a processor carries out a single instruction on multiple data items at the same time
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24
Q

What is the the purpose of Multiple Instruction Multiple Data (MIMD)?

A
  • Multiple instructions are carried out on multiple data across several cores
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25
Q

What is distributed computing?

A

Multiple computers on the same network each take part on a bigger problem

26
Q

What is an instruction set?

A
  • A set of all instructions written in machine code that can be recognised and executed by a given processing unit/CPU
27
Q

What are the features of Complex Instruction Set Computer (CISC)?

A
  • Aims to complete the task in as few lines of assembly code as possible
  • Complicated hardware and circuitry so it can understand and execute a series of operations
  • Multiple machine/clock cycles per instruction
  • Makes more efficient use of RAM
  • Used in laptop and desktop computers
28
Q

What are the features of Reduced Instruction Set Computer (RISC)?

A
  • Aims to use simple instructions that will be executed within a single clock cycle
  • Requires less complex hardware, leaving room for cache and registers
  • Used in smartphones and embedded systems
  • Heavy use of RAM (can cause bottlenecks if limited)
29
Q

What is a co-processor?

A
  • Any additional processor used for a specialised task
  • Improves overall speed of computer by executing concurrently with the CPU, aided by a bespoke set of electronics
30
Q

What is a GPU?

A
  • A co-processor which has a lots of independent processors working in parallel making it efficient at tasks such as image processing and machine learning
31
Q

What are the differences between GPUs and CPUs?

A
  • CPUs are generic processing units (all-rounders) / GPUs are highly specialised
  • CPUs excel at performing complex operations on small data sets (vice versa)
  • GPUs designed so a single instruction can work over a large block of similar data
32
Q

What is a multicore processor?

A
  • Single chip containing two or more independent processing units
  • Each core can fetch, decode and execute its own instructions
33
Q

How is the performance of a multicore processor enhanced?

A
  • An in chip shared cache and inter-core communication
34
Q

What is parallel processing?

A
  • The process of program instructions by dividing them between multiple processors or processor cores
35
Q

What are the limitations of parallel processing?

A
  • It can speed up computation depending on:
  • The task being carried out
  • If the software being designed makes use of parallel processing
36
Q

What is an input?

A
  • Any device that allows you to pass information from the outside world into a computer system
37
Q

What is an output?

A
  • Any device that can take data stored in digital form and convert it into another format humans can process such as sound, images and vibrations
38
Q

What is a storage device?

A
  • Any device used for either temporary or permanent storage of data
  • Can be internal or external
39
Q

What is optical storage?

A
  • Data is stored in the reflectivity (pits and lands) of a surface and is read from and written to by a laser
40
Q

What are some examples of optical storage?

A
  • CD
  • DVD
  • Blu-ray
41
Q

What are the advantages of optical storage?

A
  • Cheap
  • Portable
  • Lightweight
42
Q

What are the disadvantages of optical storage?

A
  • Slow access times
  • Prone to scratches
43
Q

What is magnetic storage?

A
  • Relies on the polarisation of magnetic particles to store bits on a magnetic material which is typically moved mechanically
44
Q

What are some examples of magnetic storage?

A
  • Hard Disk Drives
  • Floppy Disks
  • Magnetic Tape
45
Q

What are the advantages of magnetic storage?

A
  • Cheap
  • High data capacity
46
Q

What are the disadvantages of magnetic storage?

A
  • Slow access times
  • Fragile
47
Q

What is solid state/flash storage?

A
  • Solid state technology that stores data on a collection of memory chips
  • No moving parts as data is accessed by software
48
Q

What are some examples of solid state/flash storage?

A
  • SSDs
  • Memory Sticks
  • Flash cards
49
Q

What are the advantages of solid state/flash storage?

A
  • Durable
  • Fast access times
50
Q

What are the disadvantages of solid state/flash storage?

A
  • Expensive
  • Limited read/write cycles
51
Q

What is RAM?

A
  • Temporary storage of data and instructions
  • Holds data and instructions that are currently being used by the CPU and computer
  • Volatile (data is lost when power is turned off)
52
Q

What is ROM?

A
  • Small piece of read only memory located on the motherboard
  • Contains the start up instructions of the computer (bootstrap)
  • Non volatile
53
Q

What is a Power On Self Test?

A
  • Sends signals to all connected components and makes the CPU aware they all exist
54
Q

What do the first instructions in ROM perform when the computer is turned on?

A
  • A Power On Self Test
55
Q

What is opcode?

A
  • What we need to do (operation)
56
Q

What is operand?

A
  • What do we need to do it to
57
Q

What occurs during the fetch phase?

A
  • Address from the PC is copied to the MAR
  • Instructions in MAR is copied to the MDR by the data bus, simultaneously contents of the PC increase by 1
  • Value of the MDR is copied to the CIR
58
Q

What occurs during the decode phase?

A
  • Instruction in the CIR is split into opcode and operand
59
Q

What occurs during the execute phase?

A
  • Opcode is executed on the data
60
Q

What is cloud storage?

A
  • The concept of receiving and retrieving data on the internet in the cloud instead of a local storage device

OCR A Level Computer Science (34 decks)

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