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A Level Computer Science > Computer Organisation and Architecture > Flashcards

Computer Organisation and Architecture Flashcards

1
Q

What is the processor?

A
  • Executes program instructions in order to run applications
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2
Q

What is the main memory?

A
  • Includes RAM, random access memory
  • Includes ROM, read only memory
  • Stores program instructions and frequently used data
  • Much faster than secondary storage
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3
Q

What is a bus?

A
  • A series of parallel wires that connects internal components of a computer system, allowing signals to be passed between them
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4
Q

What is the width of a bus?

A
  • The number of parallel wires in a bus
  • It has a direct relationship to the number of bits it can transfer
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5
Q

What is the address bus?

A
  • Used to transport memory addresses
  • Specifies where in memory, data is to be sent or retrieved
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6
Q

What happens if you increase the width of the address bus?

A
  • Increases the range of addresses that can be specified by double
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7
Q

What is the data bus?

A
  • Sends data and instructions to and from the components of a computer system
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8
Q

What happens if you increase the width of the data bus?

A
  • Increases the volume of data that can be transferred at any one time
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9
Q

What is the control bus?

A
  • Used to carry control signals that regulate the operation of the computer system
  • Carries the computer’s clock signal
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10
Q

What is an I/O controller?

A
  • Pieces of hardware that control the communication of data between the processor and external hardware devices
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11
Q

What is Harvard architecture?

A
  • The processor uses two separate main memory locations
  • One for instructions and the other for data
  • These can be given characteristics such as:
    • Instructions could be made read-only so that instructions cant be changed
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12
Q

When is Harvard architecture used most?

A
  • Embedded systems such as digital signal processing
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13
Q

What is Von Neumann architecture?

A
  • Both instructions and data are stored together in the same memory
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14
Q

Why might Von Neumann perform worse than Harvard architecture?

A
  • The same buses have to be shared for fetching both instructions and data in Von Neumann
  • Therefore, systems based on Von Neumann often perform worse than those on Harvard
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15
Q

When is Von Neumann architecture used most?

A
  • Everyday general-purpose computer systems like laptops
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16
Q

What is the stored program concept?

A
  • Machine code instructions stored in main memory are fetched and executed serially by a processor that performs arithmetic and logical operations
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17
Q

What is inside a processor?

A
  • An arithmetic logic unit (ALU)
  • A control unit
  • Registers
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18
Q

What is the arithmetic logic unit (ALU)?

A
  • Performs arithmetic and logic operations
  • Arithmetic includes maths operations
  • Logic includes Boolean operations
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19
Q

What is the control unit?

A
  • Responsible for controlling the various components of the processor
  • Controls the fetch-execute cycle
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20
Q

What are registers?

A
  • Small storage locations used to hold data temporarily
  • Have high read and write speeds
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21
Q

What are general-purpose registers?

A
  • Used as storage for any data that is required by instructions during execution
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22
Q

What are special-purpose registers?

A
  • Assigned to the storage of specific information
  • Examples include:
    • Program counter
    • Current instruction register
    • Memory address register
    • Memory buffer register
    • Status register
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23
Q

What is the program counter (PC)?

A
  • Holds the memory address of the next instruction to be execute in the fetch-execute cycle
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24
Q

What is the current instruction register (CIR)?

A
  • Holds the instruction that is currently being executed by the processor
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25
Q

What is the memory address register (MAR)?

A
  • Stores the memory address of a memory location that to is be read from or written to
26
Q

What is the memory buffer register (MBR)?

A
  • Holds the contents of a memory location that has been read from or data that is to be stored
  • Also referred to as the memory data register (MDR)
27
Q

What is the status register (SR)?

A
  • Contains a number of bits, the values of which can change to indicate the occurence of an interrupt
28
Q

What is the system clock?

A
  • Found in the processor
  • Generates a timing signal which changes at a regular frequency
  • Used to synchronise communication between the components of the processor and the rest of the computer system
29
Q

What is the fetch stage of the fetch-decode-execute cycle?

A
  • The next instruction to execute is retrieved from main memory
    1) The contents of the PC is copied to the MAR
    2) The contents of the MAR is transferred to main memory by the address bus
    3) The instruction is sent from main memory to the MBR by the data bus
    4) The PC is incremented by one
    5) The contents of the MBR is copied to the CIR
30
Q

What is the decode stage of the fetch-decode-execute cycle?

A
  • The fetched instruction is decoded
    1) The contents of the CIR is decoded by the control unit
    2) The decoded instruction is split into two parts: opcode and operand
31
Q

What is the execute stage of the fetch-decode-execute cycle?

A
  • The instruction is carried out
    1) Any data required by the instruction that isn’t present in the registers is fetched
    2) The instruction is carried out
    3) Results of any calculations are stored in general purpose registers or main memory
32
Q

How are interrupts checked for in the fetch-decode-execute cycle?

A
  • Between each execute and fetch stage
  • The content of the status register is checked for changes
  • These are changes which could signal the occurence of an interrupt
33
Q

What are interrupts?

A
  • Signals sent to the processor by another part of the computer
  • It requests the attention of the processor
  • Can be handled using the vectored interrupt method
34
Q

What is the vectored interrupt method?

A
  • When an interrupt occurs, the processor stops executing the current program and places the content of its registers onto the system stack
  • The processor loads the appropriate interrupt service routine
  • Once finished, the processor restores the volatile environment from the system stack and resumes execution
35
Q

What is immediate addressing?

A
  • The value specified in the operand is to be treated as the actual value to be used
36
Q

What is direct addressing?

A
  • The value specified by an operand signifies a memory address
37
Q

How does the number of cores affect the processors performance?

A
  • Directly affects the performance
  • Each core can perform its own fetch cycle independently of others
  • Different applications can be allocated different cores
38
Q

What is cache memory?

A
  • A small portion of incredibly fast memory
  • Has high read and write speeds
  • Used to store frequently used info and reduces time wasted in fetching the same info from main memory
39
Q

How does cache memory affect the processors performance?

A
  • The more cache, the more info can be stored in the processor and the more time it can save in fetching info from main memory
40
Q

What is clock speed?

A
  • The frequency of pulses generated by the system clock
41
Q

How does clock speed affect the processors performance?

A
  • The higher the frequency, the more cycles of the fetch-decode-execute cycle can be completed in the same period of time
42
Q

What is word length in terms of the processor?

A
  • A word is a group of bits that is treated as a group of bits by the processor
  • The length is the number of bits assigned
43
Q

How does word length affect the processors performance?

A
  • Higher word lengths allow for more bits to be transferred and manipulated as a single unit
44
Q

What is a barcode?

A
  • Printed diagrams that consist of light and dark portions
  • Contain info which can be read by a computer using a barcode reader
  • Two types:
    • 1D
    • 2D
45
Q

What is the difference between a 1D and 2D barcode?

A
  • 2D can contain more information in the same amount of space as a 1D
  • 2D requires more processing in order to extract contents
46
Q

Describe the principles of operation of a barcode reader

A
  • Consists of a laser light source, a lens, photo diodes and a mirror
  • The mirror directs light from the laser onto a printed barcode
  • The light reflected by the barcode passes through the lens and is incident on the photo diode
  • The photo diode turns light into electrical charge which can be measured and processed to from a digital signal
  • Light portions of a barcode reflect the light
  • Dark portions absorb light
  • The pattern of light and dark corresponds to binary 1s and 0s
47
Q

Describe the principles of operation of a digital camera

A
  • Consists of a lens that focuses light onto a sensor
  • These sensors are either:
    • CMOS (complementary metal oxide semiconductor)
    • CCD (charged coupled device)
  • These sensors convert light into electrical charge and consists of cells, each of which represents a pixel in the image
  • The shutter regulates the path of light between the lens and sensor
48
Q

Describe the principles of operation of a laser printer

A
  • An output device that produces images on paper from digital signals
  • Consists of a laser light source, a mirror, a drum, a toner roller and fusers
  • The drum is positively charged
  • The laser is directed at the drum’s surface by the mirror discharge parts, leaving behind an impression of the page in electrical charge
  • The toner roller dispenses negatively charged toner onto the drum
  • Toner is attracted to the positively charged portions of the drum and applied to the paper
  • The paper is heated by fusers, fixing the toner to the paper
49
Q

How do colour printers work?

A
  • Applies the same process of laser printer
  • But with 4 different colours of toner:
    • Cyan
    • Yellow
    • Magenta
    • Black
  • Known as CYMK
50
Q

What is RFID?

A
  • Stands for Radio Frequency Identification
  • A method of transferring info wirelessly between a tag and a reader
51
Q

What is an RFID tag?

A
  • Contains a chip with small memory
  • Contains a coil of wire, attached to the chip, which acts as an antenna
  • Are either passive:
    • Induces power from the reader to operate the chip
  • Or active:
    • Contains a small power supply like a battery
52
Q

Describe the principles of operation of RFID

A
  • The reader emits radio waves which are picked up by the tag’s antenna
  • The power induced from these waves is enough to power a passive tag’s chip
  • The chip uses its antenna to emit a radio wave, containing the chip’s information
  • This wave is picked up by the reader which decodes the info
53
Q

What are hard disk drives (HDD)?

A
  • Consists of circular platters that are magnetic
  • Between 500 GB to 5 TB
  • Susceptible to damage from movement
54
Q

How do HDD store data?

A
  • Above each platter, hovers an actuating arm on which a read/write head is mounted
  • The read/write head changes the magnetic polarity of parts of the platter
  • The actuating arm allows the read/write head to access all parts of each platter
  • Data is written in concenctric tracks, each of which is divided into sectors
  • The platter rotates thousands of times per minute, allowing for good speeds
55
Q

How can the HDD storage capacity be increased?

A
  • Adding more platters
  • Decreasing the width of tracks
56
Q

What are solid state drives (SSD)?

A
  • Consists of non-volatile NAND flash memory cells and a controller that manages the structure of data on the drive
57
Q

How do SSD store data?

A
  • Memory cells are formed of floating gate transistors which store info by trapping electrical charge
  • Data is stored in pages, which are combined to form blocks
  • If new info is to be written, the entirety of a page must be erased
58
Q

Explain the advantage of SSD over HDD?

A
  • SSD has no moving parts so:
    • is capable of far higher read and write speeds than HDD
    • suitable for use in portable devices
59
Q

What are optical disks?

A
  • Includes CDs, DVDs and Blu-rays
  • Stores info which can be read optically by a laser
  • Can be read-only, recordable or rewritable
  • Have one continuous track which spirals out from the disk centre
60
Q

How do read only disks store data?

A
  • Uses pits and lands
  • Pits are burnt into the disk by a high-power laser which permanently deforms the surface
  • A low-power laser is passed over the surface of a disk:
    • When the laser is on a land, the light reflects back onto a photo diode
    • When the laser is on a pit, the light from a beam is scattered in different directions
  • The pattern of reflections and scatters can be converted into a digital signal
61
Q

How do rewriteable and recordable disks store data?

A
  • Rewriteable:
    • A pattern of reflections and scatters is created by an opaque dye on the disk’s surface
      • If there is no dye, the laser is reflected
      • If there is dye, the laser beam is absorbed
  • Recordable:
    • Use a photosensitive dye which changes from opaque to transparent

A Level Computer Science (6 decks)

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