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Computer Science > Unit 5 > Flashcards

Unit 5 Flashcards

1
Q

What does the processor do?

A

The processor responds to processes and instructions that drive the computer, it contains the control unit, AL, and the registers

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2
Q

What does the control unit do?

A

The control unit coordinates and controls all the operations carried out by the CPU and operates the fetch execute cycle as well as accepting the next instruction and braking down the processing into several steps

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3
Q

What is the fetch stage in the FE cycle?

A

Causes the next instruction to be asked from the main memory

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4
Q

What is the decode stage?

A

It decodes the instruction

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5
Q

What is the execute stage?

A

Causes the instruction to be carried out

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6
Q

What does the ALU do?

A

The arithmetic logic unit can perform both arithmetic or logical operations including adding, subtracting comparisons as well as bitwise logical operations (AND, ORs etc) and shift operations

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7
Q

What are registers?

A

Registers are special memory cells that operate at very high speeds, and were all ALU operations take place

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8
Q

What is a bus?

A

A bus is a set of parallel wires connecting two or more components of a computer.

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9
Q

What are the three buses that the processor is connected to?

A

Address bus, data bus, and control bus

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10
Q

What are the three main buses known as?

A

The system bus

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11
Q

How many devices can transmit along the bus at once?

A

Only one as it has a shared transmission media

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12
Q

Which way does the control bus go?

A

The control bus goes in both directions between everything

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13
Q

What are control lines?

A

The induvidual wires in the control bus?

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14
Q

Why are control lines provided?

A

To ensure that access and use to the data and addresss bus doesn’t lead to collisions

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15
Q

What is the control buses purpose?

A

Its purpose is to transmit command, timing, and specific status between system componenets

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16
Q

Examples of control lines

A

Memory write, memory read, interrupt request, bust request, bus grant, clock, and reset

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17
Q

What does the data bus consit of?

A

The data bus consits of 8,16,32, or 64 seperate lines provide by a bi-directional bath for moving data and instructions between componenets

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18
Q

Is the data bus always bi direction?

A

Not always, for example between the VDU output controller it is only one way

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19
Q

Why is the width of the data bus key for system performance?

A

The wider the data bus is, the more data it can carry out once meaning that it can fetch more data at once.

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20
Q

What is memory divided into?

A

Words

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21
Q

What is a word?

A

Each word is a fixed size group of digits (8,16, etc) which is handeled as a unit by the processor

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22
Q

What does the width of the address bus determine?

A

The maximum possible memory capacity of the system

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23
Q

What is the address bus used for?

A

When a processor wishes to read a word of data from memory it puts the address of the desired word on the address bus

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24
Q

Where does the address bus go from/ to?

A

The address bus goes from the processor to all the other components

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25
Q

What is an input/ output controller?

A

An I/O controller is a devers which interacts between and input or output device and the processor

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26
Q

What does each devices controller connect to?

A

The control bus

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27
Q

What do the I/O controllers do?

A

They recieve input and output requests from the processor and then send device specidic control signals to the device they control as well as managing the data flow to and from from the device

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28
Q

What does the I/O controllers electric circuit consit of?

A

An interface that allows connection of the controller to the system or I/O bus, a set of data, command, and status registers, an interface that enables connection of the controller to the cable connecting the device to the computer

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29
Q

What is an interface?

A

An interface is a standardised form of defining connecting things such as signals, number of pins/ sockets and voltage levels.

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30
Q

What is an example of an interface?

A

A USB

31
Q

What is a peripheral?

A

An external device

32
Q

What is Von Neuman architecture?

A

It specifies the basic components of the computer and processor in which a shared memory and bus is used for both data and instructions.

33
Q

What is the stored program concept?

A

Machine code instructions are fetched and executed serially by a processor that performs arithmetic and logical operations

34
Q

What does the stored program conecpt mean?

A

A program must be resident in main memory to be executed, the machine ccode instructions are fetched from memory one at a time, decoded and then executed

35
Q

What is harvard architecture?

A

The harvard architecture has physically separate memory for both data and instructions

36
Q

Where is harvard architecture used?

A

It is used with embedded digital signal processing systems

37
Q

What is an advantage of harvard architecture?

A

Different memorys can have different characterstics eg instructions in ROM while data in write memory or having more of one less of another, can be faster the von Neumann architecture because data and instructions can be fetched in parallel

38
Q

What are the componenets of the processor?

A

ALU, control unit, system clock, general purpose registers and dedicated registers

39
Q

What does the system clock do?

A

The system clock generates a series of signals switching between 0 and 1 which synchronises CPU operations

40
Q

Typically, how many general purpose registers are there?

A

16

41
Q

Where do all arithemtic or shift operations take place and why?

A

In registers as the have very fast memorys

42
Q

What is another name for a general purpose register and when is it used?

A

Acummulator used when there is just a single register in which to store the result of each calculation

43
Q

What kind of computers still use an accumulator?

A

Special purpose processors

44
Q

What is the PC (register)?

A

The program counter holds the address of the next instruction to be executed

45
Q

What is the CIR (register)?

A

The current instruction register holds the current instruction

46
Q

What is the MAR (register)?

A

The memory address register holds the address of the memory location from which data/ instruction is to be fetched or which data is being written to

47
Q

What is the MBR (register?

A

The memory buffer register is used to temporarily store data.

48
Q

What is the SR register?

A

The status register contains bits that are set or cleared depending on the result of an instruction

49
Q

What happens in the fetch stage of the fetch execute cycle?

A

The address of the next instructio is copied from the PC to the MAR and is sent via the address bus to main memory/ Then the instruction is returned along the data bus to the MBR and the PC is incremented. Then the contents of the MBC is copied to the CIR.

50
Q

What happens in the decode stage of the fetch-execute cycle?

A

The instruction held in the CIR is decoded and split into opcode and operand. The operand is used to determine which type of hardware is needed and additional data is fetched if necarsary.

51
Q

What happens in the execute phase of the fetch-execute cycle?

A

The instruction is executed, using the ALU if necessary and results are stored in the accumulator, general purpose registers or memory

52
Q

What factors affect processor performance?

A

Number of cores, amount/ type of cache, clock speed, word length, address/ data bus width

53
Q

Why might does having multiple cores speed up performance?

A

Each core can carry out one fetch/execute cycle at once, so more cores more cycles can be carried out.

54
Q

Why might having multiple cores not affect the performance?

A

Software doesnt always take advantage of both cores.

54
Q

What is cache?

A

A very small amount of expensive but very fast memory inside or very neary to the CPU

55
Q

What are the different levels of cache?

A

Level 1 is the fastest and smallest, followed by level 2 and then level 3

55
Q

Why does the amount of cache affect processor speed?

A

When instructions are fetched they are then copied into cache so the next time they are fetched its much quicker however once it is filled, unused data or instructions are replaced by more recent ons negating the impact

56
Q

Why does clock speed affect processor performance?

A

All processor activities begin on a clock pulse so the greater the speed the faster instructions will be executed

57
Q

What is the word size?

A

The number of bits the CPU can simulatneously process

58
Q

How does word size/length affect processor performance?

A

The larger the word length the faster they will be

59
Q

How does the address bus width affect processor performance?

A

The width of the address busdetermines the maximum memory that can be directly referenced

60
Q

How does the width of the data bus affect the proccesor performance?

A

The width of the data bus determines how many bits can be transferred simulataneously are is usually the same as the word size of a computer

61
Q

What is an interupt?

A

An interrupt is a signal sent by a software program or hardware device to the CPU

62
Q

When do software interrupts occur?

A

When an application program terminates or request certain services to stop operating.

63
Q

When do hardware inpterupts occur?

A

They may occur when an I/O operation is incomplete eg. when a printer runs out of paper

64
Q

What happens when the CPU receives an interrupt?

A

It suspends execution of the running program or process and puts the values of each register and the PC onto the system stackwhile an interupt service routine is called to deal with the interupt

65
Q

What happens once the interupt has been serviced?

A

The original values of the registers are retrieved from the stack and the fetch-execute cycle continues from when it is left off

66
Q

How often are interupts tested for?

A

At the end of each instruction cycle

67
Q

What is the processor instruction set?

A

Each processor has a unique instruction set comprimising of the instructions that are supported on its hardware

68
Q

What types of instructions does the processor set typically include?

A

Data transfer, arithmetic operations, comparison operators, logical opertings, branching, logical, and halt

69
Q

What does machine code comprimise of?

A

Each machine code has a number of bits allocated to the opcode and the operand which depends on the architecture of the processor

70
Q

What is immediate addressing?

A

When the operand is the actual value.

71
Q

What is direct addressing?

A

Where the operand holds the memory of the value to be operated on

Computer Science (8 decks)

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