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CS A Level Paper 2 > Fundamentals of computer organisation and architecture > Flashcards

Fundamentals of computer organisation and architecture Flashcards

1
Q

The address bus in the current system is made up of 16 lines. The data bus in the current system is 32 bits wide.

State the number of additional lines required in the address bus to doulbe the number of available addresses.

A

1

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2
Q

Describe the impact of increasing the width of a data bus [3 marks]

A
  • More data can be transferred simultaneously.
  • Decreases the time taken to transfer data into/out of the processor.
  • Increases the performance of the computer system
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3
Q

Explain what happens when an interrupt occurs during the fetch-decode-execute cycle (4 marks)

A
  1. Current state of the processor is saved in a stack
  2. The source of the interrupt is identified
  3. The appropriate Interrupt Service Routine (ISR) is called
  4. The saved state of the processor is restored
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4
Q

Describe the difference in design between the Harvard and von Neumann architectures (2 marks)

A

In von Neumann architecture, both programs and data use the same main memory OR data bus (1)

In Harvard architecture, programs are stored in one block of memory and data in another OR programs and data are fetched using different buses (1)

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5
Q

Suggest typical uses for a computer system using Harvard architecture

A
  • Embedded system
  • digital signal processing
  • any reasonable example of an embedded system
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6
Q

Andrew has purchased a new laptop package that includes an external DVD drive, HDD backup drive, an internal SSD and a laser printer.

Explain the need for a secondary storage device in a computer system

A

To save data/programs so that they can be accessed at a later time

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7
Q

Andrew has purchased a new laptop package that includes an external DVD drive, HDD backup drive, an internal SSD and a laser printer.

State the name of an optical device comes with Andrew’s computer

A

DVD drive

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8
Q

Andrew has purchased a new laptop package that includes an external DVD drive, HDD backup drive, an internal SSD and a laser printer.

State the name of a magnetic device that comes with Andrew’s computer.

A

(External/backup) HDD

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9
Q

Andrew has purchased a new laptop package that includes an external DVD drive, HDD backup drive, an internal SSD and a laser printer.

Describe five advantages for using an internal SSD instead of an HDD in Andrew’s laptop (5 marks)

A
  • Smaller physical size
  • Faster read/write times
  • Less likelihood of damage when moved
  • More reliable due to lack of moving parts
  • Lower power usage
  • Less noise due to lack of moving parts
  • Less heat generated due to lack of moving parts
  • Not susceptible to magnetism
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10
Q

Explain the principles of operation of a laser printer

A

Indicative response

  • Printer contains positively charged toner.
  • Printer generates a bitmap image based on the data received.
  • Print drum coated with a positive charge.
  • Laser beam directed by a mirror.
  • Laser beam fired at drum.
  • Laser switches on and off.
  • Laser beam removes charge where the ink should be attracted.
  • Charged portions of the drum attract the toner.
  • In colour printers, each colour has its own drum.
  • Paper is rolled over the drum/toner is transferred to the paper.
  • Fuser seals the toner onto the paper
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11
Q

A professional photographer has purchased a new computer with an internal magnetic hard drive, internal solid sate drive, an optical drive and an external magnetic drive.

Provide reasons why the photographer has chosen a magnetic hard drive as an external device rather than a salid-state drive.

A
  • Lower cost per unit of storage for magnetic hard drives OR higher cost per unit for SSDs.
  • Larger capacity available for magnetic hard drives OR smaller capacities typical for SSDs.
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12
Q

A professional photographer has purchased a new computer with an internal magnetic hard drive, internal solid sate drive, an optical drive and an external magnetic drive.

The photographer wishes to send a collection of 300 wedding photos to a client, using physical media. Compare and contrast the advantages of sending the images on a DVD, USB stick or portable magnetic hard drive, making it clear which you think is the most appropriate.

A

Indicative response

DVD/Optical

Advantages:

  • Cheap per disc
  • Small physical size/easy/cheap to post
  • Can view photos through a DVD player on a TV

Disadvantages:

  • Slow to read/write
  • Not every computer has an optical drive
  • Easily scratched/damaged

USB stick/solid state

Advantages:

  • Fast read/write time
  • Small physical size/easy/cheap to post
  • Almost all devices have a USB socket
  • Can view photos through a USB socket on a TV
  • Resilient/difficult to damage
  • Cheaper than a magnetic hard drive

Disadvantages:

  • More expensive than a DVD
  • Need to make sure there is sufficient capacity

Magnetic hard drive

Advantages:

  • Very large storage capacity
  • Low price per GB

Disadvantages:

  • Large/heavy/expensive to post
  • Large price per item
  • Unnecessarily large storage capacity
  • Susceptible to damage during shipping

(Reward any reasonable conclusion in favour of a suitable medium except magnetic hard drive.)

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13
Q

Describe four possible alterations to the design of a processor that could lead to faster execution (8 marks)

A
  • Increased cache size (1) so that more of the most frequenctly used programs/data can be made available for fast access (1)
  • Increased number of cores (1) so that more instructions can be executed simultaneously (1)
  • Increased clock speed (1) so that more instructions can be executed in the same amount of time (1)
  • Wider data bus (1) for greate throughput of data into the processor (1)
  • Larger word length (1) for larger values (1)
  • Wider address bus (1) allows for larger allocation of main memory/RAM (1)
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14
Q

The diagram shows the internal architecture of a computer system.

What is the component for label ‘a’ in the diagram? (1 mark)

A

Any suitable output device

  • monitor
  • speaker
  • printer
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15
Q

The diagram shows the internal architecture of a computer system.

What is the component for label ‘b’ in the diagram? (1 mark)

A

Processor/CPU

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16
Q

The diagram shows the internal architecture of a computer system.

What is the component for label ‘c’ in the diagram? (1 mark)

A

Main memory/RAM

17
Q

The diagram shows the internal architecture of a computer system.

What is the component for label ‘d’ in the diagram? (1 mark)

A

Any suitable input device

  • keyboard
  • mouse
  • microphone
  • scanner
18
Q

The diagram shows the internal architecture of a computer system.

What is the component for label ‘e’ in the diagram? (1 mark)

A

Address bus (unidirectional - away from the CPU)

19
Q

The diagram shows the internal architecture of a computer system.

What is the component for label ‘f’ in the diagram? (1 mark)

A

Data bus (sends data to the output device, receives from the input device)

20
Q

The diagram shows the internal architecture of a computer system.

What is the component for label ‘g’ in the diagram? (1 mark)

A

Control bus (bidirectional in all locations)

28
Q

The table below describes the six steps in the fetch-decode-execute cycle, though not in the correct order

  • Execute
  • MBR
  • PC
  • MAR
  • Decode
  • CIR

State the first step

A

MAR

the contents of the program counter are copied into the memory address register

29
Q

The table below describes the six steps in the fetch-decode-execute cycle, though not in the correct order

Execute

MBR

PC

MAR

Decode

CIR

State the step that follows MAR

A

PC

the program counter is incremented

30
Q

The table below describes the six steps in the fetch-decode-execute cycle, though not in the correct order

Execute

MBR

PC

MAR

Decode

CIR

State the step that follows PC

A

MBR

The contents of the memory location addressed by the memory address register are copied to the memory buffer register/memory data register

31
Q

The table below describes the six steps in the fetch-decode-execute cycle, though not in the correct order

Execute

MBR

PC

MAR

Decode

CIR

State the step that follows MBR

A

CIR <= [MBR]

The contents of the memory buffer regiter are copied to the current instruction register

32
Q

The table below describes the six steps in the fetch-decode-execute cycle, though not in the correct order

Execute

MBR

PC

MAR

Decode

CIR

State the step that follows CIR

A

Decode

The contents of the current instruction register are decoded (by the control unit)

33
Q

The table below describes the six steps in the fetch-decode-execute cycle, though not in the correct order

Execute

MBR

PC

MAR

Decode

CIR

State the last step

A

Execute

the instruction is executed

34
Q

Explain why

PC

and

MBR

take place simultaneously in the fetch-decode-execute cycle

A

Both steps use separate registers/neither step directly impacts the data required for the other

35
Q

The table below describes the six steps in the fetch-decode-execute cycle, though not in the correct order

Execute

MBR

PC

MAR

Decode

CIR

State which two steps occur simultaneously

A

PC

MBR <= [Memory] addressed

36
Q

Explain what happens when an interrupt occurs during the fetch-decode-execute cycle (4 marks)

A
  • Current state of the processor is saved in a stack (1)
  • the source of the interrupt is identified (1)
  • the appropriate Interrupt Service Routine (ISR) is called (1)
  • the save state of the processor is restored (1)
37
Q

Explain how the performance of a system might be improved from a hardware perspective. (22 marks! 11 point, expand on each)

A
  1. Replace the processor with one which has more cores
  2. Replace the processor with one which has more cache memory // increase the amount of cache memory
  3. Replace the processor with one which runs at a faster clock speed NE. faster processor Use a parallel processor architecture // use more processors which can work in parallel Use a processor with a bigger word size
  4. Use a processor that makes (better) use of pipelining
  5. Install more RAM // main memory // primary memory
  6. Use RAM // main memory // primary memory with a faster access time
  7. Replace HDDs with SSDs // Replace HDDS with HDDs that can read data at a faster rate
  8. Defragment the HDD
  9. Replace the motherboard with one which has buses which run at a faster clock speed Replace the motherboard with one which has more lines in the data bus
  10. Use the Harvard architecture
  11. Distribute the processing across multiple servers
38
Q

Explain how the performance of a system might be improved from a network perspective. (14 marks, 7 points, expand on each)

A
  1. Replace the network cable with cable that has a higher bandwidth // replace copper cable with fibre-optic cable A. Ethernet cable for fibre-optic NE. higher bandwidth network
  2. Replace any wireless/WiFi connections with wired ones
  3. Replace the network cards with ones that can transmit data at a higher bitrate
  4. Consider the overall network design eg how the network is divided into subnets A. split the network into subnets
  5. Use a star topology (instead of a bus)
  6. Consider using a more efficient protocol for the data across the network
  7. Add additional wireless access points
39
Q

Explain how the performance of a system might be improved from a database/software perspective. (22 marks, 11 points, expand on each)

A
  1. Use a more efficient technique for controlling concurrent access to the database // replace record/table locks with serialisation/timestamp ordering/commitment ordering
  2. Replace the database software with software that uses more efficient algorithms for tasks A. examples eg replace linear search with binary search
  3. Use the index feature of the database to speed up searching on fields that are commonly used for this purpose
  4. Rewrite the database software in a language that is suitable for concurrent execution // use a functional programming language for the database software
  5. Ensure the software is compiled rather than executed by an interpreter // rewrite the software in assembly language/machine code
  6. Review the conceptual model of the database to see if it contains any inefficiencies such as data redundancy that could be eliminated A. normalise the database design
  7. Consider if it would be appropriate to sacrifice normalisation of the conceptual model to improve performance
  8. Use a non-relational database system A. examples eg NoSQL Distribute the data across multiple servers
  9. Try to reduce the amount of other (unrelated) software that might be running on the database server at the same time
  10. Try to reduce the number of database accesses that need to be made simultaneously // run some tasks at quiet times/overnight
  11. Purge / archive data that is no longer necessary/in use
40
Q

Describe how an instruction is fetched from main memory, during the fetch stage of the fetch-execute cycle. [4 marks]

A
  • Contents of Program Counter/PC transferred to Memory Address Register/MAR
  • Address bus used to transfer this address to main memory
  • Fetched value/instruction transferred using the data bus
  • Contents of addressed memory location loaded into the Memory Buffer Register/MBR
  • Transfer content of Memory Buffer Register/MBR to the Current Instruction Register/CIR

A. Memory Data Register / MDR for MBR
I. Incrementing of program counter, even if incorrect
NE. Points made using register transfer notation only eg CIR[MBR]

41
Q

During the decode and execute stages of the fetch-execute cycle the instruction that is being processed is stored in the CIR. Explain why the instruction could not be processed directly from the MBR. [2 marks]

A

To execute/carry out the instruction other data may need to be fetched (from main memory);
A. During execute phase MBR used to store other data
A. Further instructions may need to be fetched before the instruction has finished executing, if pipelining/parallelisation is referenced explicitly in the response

Further memory fetches would overwrite the contents of the MBR // the instruction would be overwritten by further memory fetches // writing the result of executing the instruction back to main memory would overwrite the instruction / MBR contents;

A. MBR is not (directly) wired to the (processor) components that will execute the instruction which CIR is
A. The MBR is not (directly) wired to the ALU as BOD

42
Q

Explain why the Harvard architecture is sometimes used in preference to the von Neumann architecture. [2 marks]

A
  • Instruction and data can be accessed simultaneously; (1)
  • Avoid/reduce delays waiting for memory fetches
  • Instruction and data memory can have different word lengths;
  • Avoids possibility of data being executed as code (which is one method that can be exploited by hackers);

Being able to use exclusively ROM for instruction memory prevents the program being modified/hacked; A. Program cannot be accidentally overwritten (by data)

Different technologies can be used to implement instruction and data memory; Different quantities of instruction and data memory means that address lengths can differ between the two // memory address structures can differ;

43
Q

State the purpose of the operand part of an instruction and explain how the addressing mode is related to this [2 marks]

A

An operand is a value/data that will be used by an operation; [1]

The addressing mode indicates how the value in the operand should be interpreted // the addressing mode indicates if the value in the operand is a memory address/register or a data/immediate value; [1]
A. In immediate addressing the operand is the value to use and in direct addressing it is a memory address/register number
NE. Addressing mode indicates if direct or immediate addressing is used

CS A Level Paper 2 (8 decks)

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