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A-Level Computer Science & IT > 7: Fundamentals of Computer Organisation & Architecture > Flashcards

7: Fundamentals of Computer Organisation & Architecture Flashcards

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1
Q

Basic Internal Components (4)

A
  • Processor
  • Main memory
  • Input / output (I/O) controllers
  • These components are connected by the system bus, which is made up of the address, data and control bus
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2
Q

Main memory (2, 1:2)

A
  • Main memory is memory that can be accessed directly by the processor
  • Each memory location has a physical address (which is used to locate and access its contents)
  • There are two types of main memory:
    – RAM is volatile working memory, which is used by the processor in the fetch-execute cycle and stores instructions and data currently in use
    – ROM is non-volatile and stores information, which is used in the boot process of the computer system
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3
Q

Processor

A

The processor processes and completes tasks by executing program instructions

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4
Q

Bus

A

Connects components of a computer system by transferring data between them

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5
Q

Address Bus (4)

A
  • The address bus is used to specify the address of a memory location to either read or write data there
  • The address bus is unidirectional and there is a connection from the processor to main memory and I/O controllers across the address bus
  • The width of the address bus refers to its number of parallel lines, which determines the number of bits that can be used to form an address
  • Therefore, the width of the address bus determines the maximum memory capacity of a computer system
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6
Q

Data Bus (1:2, 3)

A
  • The data bus is used to transfer data and instructions:
    • Data is transferred to and from the processor, main memory and I/O controllers
    • Instructions are carried from main memory into the processor
  • The data bus is bidirectional, allowing values to be written to or read from a memory location
  • The width of the data bus refers to its number of parallel lines, which determines the number of bits that can be transferred in one operation
  • Therefore, the data bus width determines the amount of data that can be fetched at once, which affects processor performance
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7
Q

Control Bus (2, 1:7)

A
  • The control bus is used to send control signals which manage the operations that take place inside a computer system
  • The control bus is bidirectional
  • Examples of control signals:
    • Memory read
    • Memory write
    • Bus request
    • Bus grant
    • Bus busy
    • Interrupt request
    • Clock signals
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8
Q

Memory Read

A

Places data from a specific memory location (whose address is on the address bus) onto the data bus

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9
Q

Memory Write

A

Stores the data from the data bus onto a specific memory location (whose address is on the address bus)

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10
Q

Bus Request

A

Signifies that a component needs to access a bus

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11
Q

Bus Grant

A

Informs a component that it can use the bus it requested access to

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12
Q

Bus Busy

A

Signifies that a bus is not available for use as it is being used by another component

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13
Q

Interrupt Request

A

Signifies that an error or exception has occurred that requires the processor’s attention

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14
Q

Clock Signals

A

Supplies the components with clock pulses generated by the system clock

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15
Q

I/O Controllers (1:2, 3)

A
  • External (peripheral) devices are connected to the processor through I/O controllers. This means:
    • Input data can be received from input devices
    • Results of computation can be sent to output devices
  • I/O controllers provide a set of addressable registers that the processor can access to communicate with I/O devices
  • A physical port on the controller provides a connection for the peripheral. The peripheral has a cable or connector to connect it to the port. The I/O controller facilitates the exchange of data between the processor and the peripheral. The controller translates the electrical signals into the correct form
  • A device driver is needed for every peripheral. This is a piece of software that provides a software interface for the peripheral device, which enables the OS to access the functions of the hardware
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16
Q

Von-Neumann Architecture (4)

A
  • The Von-Neumann architecture stores program instructions and data in main memory
  • The same address and data buses are used to transfer instructions and data
  • https://docs.google.com/presentation/d/1py7HJi8pHccmohEDrAKt8b95MUccaP7SkL4OhR6-mvw/edit#slide=id.g346a6d8c8c_0_44
  • It is used in general purpose computer systems
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17
Q

Harvard Architecture (3)

A
  • The Harvard architecture keeps instructions and data in separate memories
  • The processor accesses these memories using separate data and address buses
  • Embedded systems such as digital signal processing (DSP) systems use Harvard architecture processors
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18
Q

Concept of Addressable Memory

A

Each memory location has an address, with which its contents can be accessed

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19
Q

Stored Program Concept

A

Machine code instructions, stored in main memory, are fetched, decoded and executed serially by a processor. Programs can be moved in and out of main memory

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20
Q

Arithmetic Logic Unit

A

The ALU performs arithmetic calculations and comparisons and logical operations

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21
Q

Control Unit (4)

A
  • It uses control signals to enable data to be read from and written to main memory
  • It decodes every instruction that the processor will execute to determine what needs to be done
  • It organises the sequence of micro-operations that need to be performed to execute an instruction
  • It uses control signals to determine the operation the ALU will carry out
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22
Q

Clock (4)

A
  • The system clock generates regular clock pulses by emitting a signal that continually oscillates between a low and a high state
  • The clock signal is used to synchronise the operations of the processor’s components
  • A rising edge is a change from a low state to a high state. The time taken between two sequential rising edges is the clock period and it corresponds to one clock cycle
  • The clock speed (measured in Hertz) is the number of clock cycles per second
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23
Q

General-Purpose Registers (3)

A
  • Registers are memory locations inside the processor
  • The processor uses registers to temporarily store and access results of operations
  • The ALU is connected to a set of general-purpose registers that keep the results of intermediate calculations, that are part of a larger computation
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24
Q

Dedicated Register (2, 1:5)

A
  • Dedicated registers are processor-based registers, which have a specific purpose
  • The registers, used in the fetch-execute cycle, are dedicated as each one has a specific role to play in each phase of the cycle
  • Examples:
    • Program counter (PC)
    • Current instruction register (CIR)
    • Memory address register (MAR)
    • Memory buffer register (MBR)
    • Status register (SR)
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25
Q

Program Counter

A

The PC holds the address of the next instruction to be executed by the processor

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26
Q

Current Instruction Register

A

The CIR holds the current instruction that the processor is executing

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27
Q

Memory Address Register

A

The MAR temporarily holds the address of the memory location that the processor needs to access to read from or write to

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28
Q

Memory Buffer Register

A

MBR temporarily holds the data that has been read from or written to main memory

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29
Q

SR (3)

A
  • The Status Register stores information about the results of the ALU’s last operation
  • Each bit in the SR indicates if an error or exception has occurred (e.g., negative / zero results or overflow bits)
  • Or to enable or disable interrupts to be raised
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30
Q

Fetch-Execute Cycle (1:5, 1, 1:5)

A
  • Fetch:
    • The contents of the PC are copied to the MAR
    • The contents of the MAR are loaded onto the address bus
    • The contents of the addressed memory location are received from the data bus and loaded into the MBR
    • Simultaneously, the PC is incremented
    • The contents of the MBR are copied to the CIR
  • Decode:
    • The control unit decodes the instruction in the CIR, by splitting it into opcode and operand
  • Execute:
    • If necessary, data is fetched from or stored in memory
    • The opcode identifies the type of instruction to be performed by the processor
    • The results may be stored in a register of the accumulator
    • The status register is updated
    • If a jump is required, the PC is updated
31
Q

Processor Instruction Set

A

Set of instructions, that work with a specific processor

32
Q

Instructions consist of an ____ and one or more ____

A

Opcode, operands (value, memory address or register)

33
Q

Immediate Addressing

A

The operand is the datum

34
Q

Direct Addressing

A

The operand is the address of the datum (address could be either main memory or register)

35
Q

Basic Machine-Code Operations (7, 1:2, 1)

A
  • Load
  • Add
  • Subtract
  • Store
  • Branching (conditional and unconditional)
  • Compare
  • Logical bitwise operations (AND, OR, NOT, XOR)
  • Logical:
    • Shift left
    • Shift right
  • Halt
36
Q

Load

A

Loads a value stored in a memory location into a specified register

37
Q

Add

A

Adds a value to another value and stores the results in a specific register

38
Q

Store

A

Stores a value from a register into a specified memory location

39
Q

Branching – Conditional

A

Branches to a specific line in the program if a condition is met. The possible conditions are equal to, not equal to, greater than and less than. A label is required to know where to jump to

40
Q

Branching – Unconditional

A

Branches to a specific line in the program. A label is required to know where to jump to

41
Q

Compare

A

Compares two operands. The results is used to perform a conditional branch

42
Q

Logical Bitwise Operator – AND

A

Performs the AND operation on the stored binary values

43
Q

Logical Bitwise Operator – OR

A

Performs the OR operation on the stored binary values

44
Q

Logical Bitwise Operator – NOT

A

Performs the NOT operation on the stored binary value

45
Q

Logical Bitwise Operator – XOR

A

Performs the XOR operation on the stored binary values

46
Q

Logical – Shift Left

A

Shifts a binary value left by the number of spaces in the operand (n). This multiplies the number by 2ⁿ

47
Q

Logical – Shift Right

A

Shifts a binary value right by the number of spaces in the operand (n). This divides the number by 2ⁿ

48
Q

Halt

A

Stops the execution of the program

49
Q

Factors Affecting Processor Performance (6)

A
  • Multiple cores
  • Cache memory
  • Clock speed
  • Word length
  • Address bus width
  • Data bus width
50
Q

Multiple Cores (3)

A
  • The more cores a computer has, the more tasks it can run in parallel, increasing the speed of execution
  • However, multicore computer systems spend time organising which cores receive which data and instructions
  • Also, the efficiency of a multicore computer system depends on if the task supports parallel processing
51
Q

Cache Memory (4)

A
  • Cache is fast, small capacity, volatile and expensive memory, near the processor, which stores frequently used data and instruction
  • When an instruction is used a lot, it is slower to fetch it from RAM every time so it is stored in cache so it can be fetched quicker
  • Most computer systems have three levels of cache. The slowest is L3 and the fastest is L1
  • Cache memory affects system performance. Larger cache means a higher quantity of frequent instructions can be accessed faster and larger lower levels of cache (namely L1) means instructions, that are more frequent, can be accessed faster
52
Q

Clock Speed (3)

A
  • Generally, the greater the clock speed, the more instructions are executed per unit time
  • However, the processing of a single instruction typically takes multiple clock cycles
  • Therefore, clock speed is a theoretical maximum and a system may not be able to actually execute X billion instructions per second (X GHz)
53
Q

Word Length (1, 1:4, 1)

A
  • Word length is the number of bits that can be processed in one go
  • Word length affects many features of a computer system:
    • It determines the size of a bit pattern that can be transferred to or from main memory in one operation
    • The size of the processor registers is the same as the word length
    • It determines data bus width
    • Each addressable memory location in main memory is the size of a word
  • The larger the word size, the greater the number of bits that can be transferred to the processor in one pass. So, with greater word length, the quicker (fewer passes) the processor can access an instruction or datum meaning performance is increased
54
Q

Address Bus Width (4)

A
  • The address bus width determines the number of bits that can be used to form an address of a memory location. The greater the address bus width, the more memory locations can be addressed
  • If the address bus width is n bits, then there are 2ⁿ addressable memory locations available for main memory
  • System performance is increased as having more memory means that the data and instruction that need to be processed will not have to be fetched from secondary storage
  • However, increasing address bus width only increases performance if all of the instructions and data can’t be held in main memory (as there aren’t enough addressable memory locations)
55
Q

Data Bus Width (3)

A
  • The data bus width determines the number of bits that can be transferred to or from a component in one operation. The greater the data bus width, the more data can be transferred between the internal components simultaneously
  • If the data bus width is n bits, then n bits and 2ⁿ different bit patterns can be transferred between the internal components in one operation
  • System performance is increased as less fetches are needed to retrieve data so instructions and data can be processed faster
56
Q

Input & Output Devices (4)

A
  • Barcode reader
  • Digital camera
  • Laser printer
  • RFID
57
Q

Barcode Reader (5)

A
  • A barcode represents data (usually about commercial products) in a machine-readable form
  • Linear barcodes use a set of parallel lines of varied width and spacing
  • The code is printed below for manual entry as well as a check digit
  • A QR (Quick Response) code usually provides a link to a website as they can store more information
  • Barcode readers use laser scanners whereas QR code scanners can be a camera and app on a mobile device
58
Q

Barcode Reader Operation (6)

A
  • A laser is directed at bar code
  • Mirror moves light beam across bar code
  • Light reflected back
  • Black / white bands reflect different amounts of light
  • Light sensor measures amount of reflected light
  • Light reflected converted into an electrical signal
59
Q

Digital Camera Operation (7)

A
  • Digital cameras are used to capture images
  • Light is focussed by the lens onto an array of sensors on the sensor chip
  • Each sensor produces an electrical signal
  • The signal represents a pixel
  • An ADC converts measurement of light intensity into digital data
  • Colour filter is applied to generate separate data values for red, green and blue colour components
  • The pixels are recorded as an array
60
Q

Laser Printer (3)

A
  • Laser printers can print quickly
  • They used powdered ink called toner
  • The quality of output is good for text but not good for photo-quality images
61
Q

Laser Printer Operation (10)

A
  • Print drum coated in positive static charge
  • Printer generates bitmap of page from the data
  • Laser beams shone on print drum via a rotating, octagonal mirror
  • Laser is modulated (turned on & off)
  • Laser reverses electric charge on drum where the image should be dark
  • Toner is given positive charge
  • Charged drum picks up toner
  • One drum/laser mechanism for each colour in CMYK
  • Paper rolled over drum to transfer toner onto it
  • Toner is fused by heated rollers and pressure
62
Q

RFID (2, 1:3)

A
  • Radio Frequency Identification allows data to be transmitted over radio waves
  • An RFID system contains a tag and a reader
  • They can be used for:
    • Tracking the movement of farm animals and identifying pets
    • Employee and student ID cards for opening doors
    • Contactless card payment
63
Q

RFID Operation (7)

A
  • RFID tag contains transmission circuitry and antenna
  • Memory on tag stores data
  • RFID reader transmits signal
  • Signal activates RFID tag if tag is passive
  • RFID tag transmits data by radio wave
  • RFID reader converts signal back into binary data
  • RFID transmits over very short range
64
Q

HDD (5)

A
  • A Hard Disk Drive is a secondary storage device
  • They contain moving parts so are less robust and more likely to fail
  • Data is represented on the disk surface by magnetised dots. Binary data is represented through two states of ‘magnetised’ and ‘non-magnetised’
  • The read-write process requires the disk to spin, which makes HDDs slow
  • The main advantage of an HDD are its capacity and cost
65
Q

Hard Disk Fragmentation (3)

A
  • Fragmentation occurs when there is insufficient contiguous space to store a file
  • If a file is fragmented, then each part of the file will be in a separate location with a link to the next location
  • If a disk is nearly full, it will take longer to find space to write file segments and to access a fragmented file
66
Q

Hard Disk Operation (6)

A
  • The disk contains one or more metal platters with a magnetic coating. Binary data is stored on the platter as series of polarised states, representing 1 or 0
  • Each platter is broken down into a set of concentric tracks, which are broken down into sectors. A contiguous group of sectors is called a cluster
  • This is the smallest unit of storage that can be addressed by the file system
  • To read and write data, the device has two mechanical arms with a read-write head (with a tiny magnet at the end)
  • There is a thin gap between the head and disk surface. The head sweeps across the tracks, while sectors pass underneath, as the disk rotates
  • The read-write head reads and changes magnetic charge
67
Q

Optical Disk (5)

A
  • Optical discs include CD (Compact Disc), DVD (Digital Versatile Disc) and Blu-ray disc
  • ‘ROM’ (Read-Only Memory) is used for distributing music, films and software
  • ‘R’ (Recordable) are write-once read-many and used for archiving data
  • ‘RW’ (Rewritable) is used for backing up data - making temporary copies
  • The availability of optical drives is decreasing from computers, music players and cars due to an increase in cloud computing
68
Q

Optical Disk Operation (2, 2:3)

A
  • Each disc has a continuous track of data arranged in a spiral
  • Data is stored in the form of pits and lands (representing 0s and 1s) on the disc surface
  • Reading:
    • Laser light is shone onto the surface of the rotating disc
    • Pits and lands reflect different amounts of light, representing data bits
    • Reflected light hits an optoelectrical device, which interprets the different light intensities as data bits
  • Writing:
    • The laser is used at a high intensity
    • The light burns dots into the chemical layer, altering the amount of light reflected
    • With RW discs, the burning process can be reversed so data can be erased and rewritten
69
Q

SSD (4)

A
  • A Solid-State Drive is an electronic device that uses flash memory and has no moving parts
  • The absence of moving parts mean they are more robust and use less energy so generate less heat
  • They have lower latency and faster transfer speeds than a magnetic disk drive
  • The number of times an SSD can be written to is finite
70
Q

SSD Operation (8)

A
  • Data is stored electronically
  • Data is stored in floating gate transistors
  • Presence of trapped charge or absence indicates 0 / 1
  • NAND memory is used
  • Data is organised into pages / blocks
  • A whole block of data must be written
  • A block must be erased before it can be overwritten
  • Controller manages the reading and writing of data
71
Q

Comparison of Capacity & Speed of Access of Various Media

A

Media | Capacity | Speed of Access
Hard Disk | 1 TB | Medium
CD | 700 MB | Low
DVD | 4.7 GB | Low
Blu-ray Disc | 25 GB | Low
SSD | 256 GB | High

72
Q

Interrupt

A

A signal sent to the processor to request immediate attention. The processor suspends what it is doing and runs the process associated with the interrupt

73
Q

ISR (2)

A
  • The OS will have an Interrupt Service Routine to process each interrupt
  • An ISR is a mini program, built into the OS or provided by a device driver
74
Q

Servicing the Interrupt (6)

A
  • If the processor receives an interrupt, it completes the current cycle of the fetch-execute cycle
  • The current contents of the registers are saved to memory so the processor can continue executing this task after servicing the interrupt
  • The PC is updated with the address of the first instruction of the ISR
  • The ISR is executed
  • The registers are reloaded with the values saved to memory
  • The processor continues executing the task before the interrupt

A-Level Computer Science & IT (11 decks)

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