7 - Fundamentals of Computer Organisation and Architecture Flashcards

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1
Q

Explain the role of the Arithmetic Logic Unit.

A

The ALU is part of the processor that processes and manipulates data. It performs arithmetic and logical operations on data supplied in registers, storing the result in a register.

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2
Q

Explain the role of the Control Unit.

A

The CU controls operation of the fetch-decode-execute cycle and sends control signals to other components of the cycle.

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3
Q

Explain the role of general-purpose registers.

A

General-purpose registers have no specific purpose and can be used by the programmer to store data, as needed.

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4
Q

Explain the role of the clock.

A

The system clock is a unit inside the processor that provides regular clock pulses that are used to sequence the operation of the processor and the movement of data around the other components of the computer.

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5
Q

Explain the role of the Program Counter.

A

The PC stores the memory address of the next instruction to be fetched and executed and is incremented as part of the fetch-decode-execute cycle.

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6
Q

Explain the role of the Current Instruction Register.

A

The CIR stores the instruction that is currently being executed by the processor. The “decode” step is also performed on the CIR.

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7
Q

Explain the role of the Memory Address Register.

A

The MAR stores the memory location where data in the MBR is about to be written to or read from. This is also the processor’s direct connection to the address bus for accessing main memory.

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8
Q

Explain the role of the Memory Buffer Register.

A

The MBR holds the data that has just been read from or is about to be written to main memory. This is also the processor’s direct connection to the data bus for accessing main memory.

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9
Q

Explain the role of the Status Register.

A

The SR stores single bit condition codes each of which indicates the outcome of arithmetic and logical operations carried out in the ALU, for example an arithmetic operation may produce a positive, negative, zero result, a carry or overflow and the corresponding condition codes are set (made 1).

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10
Q

What are registers?

A

Registers are memory locations within the processor that support fast access as well as rapid manipulation of their contents.

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11
Q

What are the major components in a processor?

A
  • Arithmetic Logic Unit
  • Control Unit
  • Clock
  • General purpose registers
  • Dedicated registers, including:
    • Program Counter
    • Current Instruction Register
    • Memory Address Register
    • Memory Buffer Register
    • Status Register
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12
Q

Explain how the Fetch-Execute cycle is used to execute machine code programs.

A

A machine code program is made up of machine code instructions which are fetched from main memory, one at a time, and executed in the processor.

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13
Q

Describe what happens in the Fetch stage of the Fetch-Execute cycle.

A

1) The address of the next instruction to be executed (held in the PC) is copied to the MAR.
2) The address bus is used to transfer this address to main memory.
3) The instruction held at that address in main memory is transferred via the data bus to the MBR.
4) The contents of the PC are incremented to hold the address of the next instruction to be executed.
5) The contents of the MBR are copied to the CIR. This frees up the MBR for the execute phase.

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14
Q

Describe what happens in the Decode stage of the Fetch-Execute cycle.

A
  • The instruction held in the CIR is decoded by the CU.

* The instruction is split into opcode and operand.

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15
Q

Describe what happens in the Execute stage of the Fetch-Execute cycle.

A
  • The opcode identifies what type of instruction it is.
  • Instructions are executed by the relevant part of the processor.
  • Further memory fetches are carried out if required.
  • For maths or logic instructions, the ALU executes the instruction.
  • The result of computation is stored in the accumulator.
  • The status register is updated.
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16
Q

Describe the role of interrupts.

A

An interrupt is a signal that is sent to the processor to request immediate attention. When the processor receives an interrupt, it suspends what it is doing and runs the process associated with the interrupt.

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17
Q

Describe the role of Interrupt Service Routines.

A

An ISR is a small program designed to respond to each interrupt. These can be provided by either the operating system or I/O device drivers.

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18
Q

Describe the effects of interrupts on the Fetch-Execute cycle.

A

1) The processor receives the interrupt.
2) The processor completes the Fetch-Execute cycle of the instruction that it was running when it received the interrupt.
3) The current contents of the processor registers (including the PC) are saved to memory.
4) The origin of the interrupt is identified so that the appropriate ISR is called.
5) All other lower priority interrupts are put on hold to allow the ISR to finish running.
6) The PC is updated with the address of the first instruction of the ISR.
7) The ISR completes its execution.
8) The processor registers are reloaded with the values that were saved to memory.
9) The lower priority interrupts that were put on hold are re-established.
10) The PC is set to point to the address of the next instruction that needs to be executed in the program that the processor was running when it received the interrupt.

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19
Q

What is a volatile environment?

A

A volatile environment is a snapshot of the information needed to execute a process from its current instruction. This contains the special purpose and general purpose registers (including the PC).

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20
Q

Explain what happens when an interrupt occurs?

A

The volatile environment is saved on the stack. The source of the interrupt is identified so the appropriate ISR is called. After the ISR has finished its execution, the volatile environment is restored.

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21
Q

Why is it important to save the volatile environment while the interrupt is being serviced?

A

Running the ISR causes the contents of processor registers to change. Unless the volatile environment is saved before these changes occur, restoring the contents of the affected registers will be impossible as will returning the processor to the exact state it was in just before executing the ISR.

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22
Q

Name 6 factors that affect processor performance.

A
  • Multiple cores
  • Cache memory
  • Clock speed
  • Word Length
  • Address bus width
  • Data bus width
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23
Q

Explain the effect on processor performance of multiple cores.

A

By having multiple cores in a computer system, parallel processing can take place. This is where a task is split up into different parts which are executed at the same time in different cores. Therefore by increasing the number of cores, the speed of execution is increased (as long as those instructions can be executed in parallel).

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24
Q

Explain the effect on processor performance of cache memory.

A

The cache is a small amount of fast memory placed near the processor which stores copies of data from frequently used memory locations, data to be written to main memory and pre-fetched instructions. The cache can be accessed much faster than main memory. By increasing the size of the cache, more data and instructions can be stored there, resulting in programs being able to run faster.

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25
Q

Explain the effect on processor performance of clock speed.

A

A processor executes a particular instruction in a set number of clock ticks or clock cycles. Therefore increasing the clock speed causes instructions to be executed at a faster rate.

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26
Q

Explain the effect on processor performance of word length.

A

Increasing the word length means that the processor can handle more data per instruction. This is useful as processing an instruction may require multiple fetches of data from main memory. Therefore, by being able to pass larger amounts of data to the processor with every pass, the system is likely to carry out instructions faster. Increasing the word length means that the processor can access a larger amount of memory through direct accessing and could also allow the processor to have a larger instruction set.

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27
Q

Explain the effect on processor performance of the address bus width.

A

The size of the address bus represents the amount of unique memory locations that are addressable. Increasing the width of the address bus will increase the number of addressable locations and therefore allows more memory to be installed on the computer.

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28
Q

Explain the effect on processor performance of the data bus width.

A

Increasing the width of the data bus means that more bits and therefore more data can be passed down it with each pulse of the clock. Therefore increasing the width of the data bus increases the rate of data transfer.

29
Q

What are the different definitions of processor performance.

A
  • Speed/Throughput - Number of instructions executed per second.
  • Scalability - could this processor cope with, say, more memory?
  • Response Time - How long does it take for a single request to be fully completed?
  • Power consumption.
30
Q

What is the three box model?

A

The three box model is the simplest way to represent the internal components of a computer system.

system bus
←—————————————→
↕↕↕
processormaininput/
memoryoutput
31
Q

What are the basic internal components of a computer?

A

The internal subsystems are:
• Processor or Central Processing Unit (CPU)
• Main memory (RAM)
• I/O controllers - input only, output only, both input and output
• Buses

32
Q

What is the role of the processor, and how does it relate to the other internal components?

A

The processor executes machine instructions that have been fetched from main memory locations. The processor selects a memory location by placing the address of the location on the address bus. The data processed by machine instructions is fetched along the data bus from main memory and the results of processing are returned in the same way. The control bus is used by the processor to assert actions and to allow devices (such as the keyboard controller) to grab the attention of the processor via the interrupt mechanism when a key is pressed.

33
Q

What is the role of main memory?

A

Main memory is memory that can be accessed directly by the processor. The main memory consists of a contiguous block of read/write, randomly accessible storage locations where instructions or data are stored as binary sequences.

34
Q

What is the role of the address bus?

A

The address bus is unidirectional and is used to select a specific memory location containing a word of data or an instruction. It does this by carrying the address of the desired location on its bus. The address bus is also used to address I/O ports during input/output operations.

35
Q

What is the role of the data bus?

A

The data bus provides a bidirectional path for moving data and instructions between system components.

36
Q

What is the role of the control bus?

A

The control bus is a bidirectional bus which is used to transport control signals that manage and orchestrate the operations that take place in a computer system between components. This includes exchanging status signals between the components and transmitting clock signals required for the coordination of instructions.

37
Q

What is the role of the I/O controllers?

A

An I/O controller is a board of electronics that enables the processor to control and communicate with a peripheral device through a I/O port. It translates signals from the device into the format required by the processor which allows the flexibility to add new devices without having to redesign the processor as each device operates using different electronic signals. It is also used to buffer data being sent between the processor and the device, so that the processor does not have to wait for the individual device to respond.

38
Q

What is the system bus?

A

The system bus is a set of parallel wires connecting independent components of a computer system and is used to pass signals between components. The signals can represent data, addresses or control information.

39
Q

What is the difference between von Neumann and Harvard architectures?

A

In von Neumann architecture, instructions and data share the same memory which the processor communicates with over a shared bus called the system bus. In Harvard architecture, instructions and data are allocated separate memories. The processor is connected to both memories by separate buses so that each memory can be accessed simultaneously.

40
Q

What are the advantages of Harvard architecture.

A
  • Instructions and data are handled quicker as they do not have to share the same bus.
  • Avoid bottleneck of single data/address bus.
  • Instructions 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.
41
Q

Where is von Neumann architecture used?

A

Von Neumann architecture is used extensively in general purpose computing systems.

42
Q

Where is Harvard architecture used?

A

Harvard architecture is extensively used in embedded systems such as digital signal processing (DSP) systems.

43
Q

What is meant by the stored program concept?

A

A program must be resident in main memory in order to be executed. Instructions are fetched and executed one at a time by the processor. Programs can be moved in and out of memory.

44
Q

Describe and explain the process with which data is originally saved onto a read only optical disk and how this is read by a consumer.

A

Pits and flats are stamped into aluminium layer. The laser in the disk drive reads the pits and flats. The pits represent 0s and flats represents 1s. The binary values are then read.

45
Q

What does the term peripheral mean?

A

An external device not directly under the control of the processor.

46
Q

What three parts do I/O controllers consist of?

A

The controller consists of three parts:
• The I/O port - to allow exchange of signals between the processor and the peripheral.
• Electronics that interface the controller to the system bus.
• Electronics appropriate for sending signals to the device connected to the computer.

47
Q

Why is it not sensible to connect peripherals directly to the processor?

A
  • Each peripheral operates in a different way.
  • Not sensible to design a processor to control every possible peripheral.
  • A new type of peripheral would require the processor to be redesigned.
  • Peripherals may operate at a different voltage from the processor.
  • Peripherals will usually operate at a slower rate than the processor.
48
Q

Describe the principles of operation of a laser printer.

A

The print drum is coated in static charge. The printer generates a bitmap image from the data. Laser beams are directed on the print drum via a rotating octagonal mirror. The laser is modulated and neutralises electric charge on the drum where image should be dark. Toner is given charge and the charged drum picks up toner. There is one drum mechanism for each colour. Toner is then transferred from drum to paper. The toner is then fused to the paper by heated rollers.

49
Q

Describe the principles of operation of a hard drive.

A

The hard disk is a magnetic medium. Binary digits are represented by magnetising spots on the disk. The hard disk is made up of platters and is divided into tracks (which are concentric circles) and sectors. The drive head moves radially, while the disk continually spins at a high speed. Data is read/written as correct sector passes under the read/write head. There is one head per platter and the head is parked when not in use.

50
Q

Ignoring any differences in price and assuming that both drives have the same capacity, state the reasons why you might choose a solid-state drive rather than a traditional hard disk drive?

A
  • Faster access speed.
  • Silent operation.
  • Less heat generated.
  • Less power required.
  • More robust due to no moving parts.
51
Q

Why are CD-ROM disks suitable for music storage?

A
  • Easily portable.
  • Enough storage to hold music files.
  • Can be read by many devices.
  • Can’t be overwritten.
  • Small form factor.
  • Can be stored in a small space.
  • Non-volatile.
  • Durable.
52
Q

What does an opcode represent?

A

It indicates the basic machine operation.

53
Q

What does an operand represent?

A

The value that the instruction operates on.

54
Q

What is the difference between direct and immediate addressing?

A

Direct addressing means that the operand is the memory address or register number of the datum whereas immediate addressing means the operand is the datum.

55
Q

During the decode and execute stages of the fetch-decode-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.

A

To execute the instruction other data may need to be fetched from main memory. Further memory fetches would overwrite the contents of the MBR.

56
Q

How does the addressing mode relate to the operand of an instruction?

A

It indicates how the value in the operand should be interpreted.

57
Q

When the processor writes data to the main memory it will make use of the address, control and data buses. Explain how each of these buses will be used during this write process.

A

The address of the memory to be written to is placed on the address bus.
The data to be written is placed on the data bus.
The signal to write is placed on the control bus.
The control bus carries a clock signal to synchronise the memory and processor.
When the write signal is received by the memory on the control bus, the data from the data bus is stored into the location identified by the address bus.

58
Q

A RFID system is made up of a transponder built into an RFID tag and an interrogator or reader. Explain the principle of operation of this RFID system.

A

The RFID reader transmits a signal to the antenna of the RFID tag. The RFID tag is energised by the signal from the reader. The transponder in the tag sends the data signal which is received by the reader.

59
Q

Explain the purpose of the check digit in a bar code.

A

To check the bar code is valid.

60
Q

Describe the principles of operation of a bar code reader, excluding the use of the check digit.

A

For a photodiode system a laser is shone at the bar code. A moving mirror moves the light beam across the bar code and the light is reflected back. White bands reflect more light than black bands. A light sensor measures the amount of reflected light which is converted into an electrical signal and analysed to determine the value encoded in the bar code.

61
Q

What is an instruction set?

A

The set of bit patterns for which machine operations have been defined. An instruction set is processor specific.

62
Q

Describe the principles of operation of a digital camera.

A

Lens focuses light onto an array of sensors on the sensor chip. Each sensor produces an electrical signal. The signal represents a pixel. The image is captured when the shutter is pressed. An ADC converts measurement of light intensity into binary data.
Firmware performs data processing to “tidy up” image. Colour filter is used to generate data separately for red, green, blue colour components. Image is recorded as an array of pixels.

63
Q

Describe the principles of operation of a solid state drive (SSD)

A

Most commonly uses NAND flash memory. Data is stored using floating gate transistors. This is a type of transistor that can trap and store charge. Data must be read in pages and written/erased in blocks. Can use single-level cells that store one bit or multi-level cells that store two bits.

64
Q

Describe how data is written to and read from a CD-R disk.

A

To write data a high powered laser makes sections less reflective.

To read a low powered laser is used to read data back from the disk

The difference between pits and lands indicates the 1s and 0s. Data is stored as a continuous spiral track.

65
Q

What are the development in the design of hard disk drives that has enabled an increase in storage capacity?

A
  • More platters
  • Greater density of each platter
  • More tracks on a platter
  • Change to perpendicular magnetic domains
  • Ability to write smaller magnetic domains
  • Use of different alloy materials for the platter
66
Q

What are the hardware components of a solid-state drive?

A
  • NAND memory
  • Controller
  • SATA interface
67
Q

What are the differences between primary and secondary storage?

A
  • Secondary storage is non-volatile
  • Secondary storage is not directly accessible to the processor
  • Capacity of primary store is limited by width of the address bus whereas there is no limit on capacity of secondary store
  • Data in primary store can be accessed more quickly than data in secondary store
68
Q

Describe the principles of operation of an optical disk drive that is used to read data from an optical disk, ushc as CD-ROM or DVD-ROM

A

With optical disks, data is stored on a spiral track. The disk spins at variable angular velocity. A low power laser is shone at the disk. Light is focussed on spot on track. Some light is reflected back from the disk. The amount of light reflected back is measured. Continuation of land/pit on the disk reflects light whereas transition between land and pit scatters light. Transition between land and pit indicates a 1 and continuation of land/pit represents 0.