Internal computer arvhitectures Flashcards

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1
Q

summarise Von neumann architecture

A

CPU, arrow, system bus, RAM, Instructions, Data

  • shared memory space for instructions and data
  • instructions and data stored in the same format
  • a single control unit it processor follows a linear fetch, decode, execute cycle
  • one instruction at a time
  • registers are used as fast access to instructions and data
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2
Q

summarise the Harvard architecture

A
  • instructions and data stored in separate memory units
  • each has its own bus
  • reading and writing data can be done at the same time as fetching an instruction
  • used by RISC processors
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3
Q

disadvantages of harvard architecture

A
  • no adaptability
  • not appropriate for general or multi purpose machines as you can’t install and uninstall programs
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4
Q

what is the stored program concept

A

the idea that instructions are fetched one at a time from main memory and executed immediately by the processor in the sequential order
- program can be replaced by loading another program into memory
- contents in memory location can be interpreted as instruction or data

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5
Q

What happens during the Fetch stage of the Fetch-Execute cycle

A
  • contents of PC transferred to MAR
  • Address bus is used to transfer this address to main memory
  • main memory content is transferred using the data bus
  • contents of memory address location is loaded into MBR
  • contents of MBR copied into CIR
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6
Q

What happens during the Decode stage of the Fetch-Execute cycle?

A
  • The Control Unit decodes the instruction held in the CIR.
  • : The instruction is split into the opcode and operand
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7
Q

What happens during the execute stage of fetch-decode-execute

A
  • if necessary, data is fetched
  • opcode identifies type of operation to be performed
  • ALU is used to carry out the operation
  • result stored in main memory
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8
Q

what does an instruction contain

A

an opcode and an operand

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9
Q

what does the opcode do

A

Tells the CPU what to do

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10
Q

what does an operand do

A

is a value or is data that will be used in an operation

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11
Q

what can the operand be

A
  • the actual data that you’re performing the operation on
  • a memory location where the data is found
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12
Q

whats the difference between direct and immediate addressing

A
  • addressing mode 01 specifies that the data is an address, not a value (direct)
  • addressing mode 00 specifies that data is a value, not an address (immediate), represented with a hashtag before the value
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13
Q

Why are registers used as a fast access to instructions and data in the von Neumann architecture?

A

Because it’s quicker to work with data in the CPU than it is to work with directly in memory

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14
Q

Examples of alternative architecture

A
  • Parallel processing-where the processor carries out a single instruction on multiple data
  • distributor computing
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15
Q

What could the operand contain?

A

It could contain the actual data or an address where the data is found

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16
Q

How to read an instruction

A

If we are using eight bits:

  • The first four bits are the opcode, but the first three bits are the basic machine operation (ADD)
  • the last bit of the opcode is the addressing mode
  • the last four bits are the operand
17
Q

How many different opcode would be available in an 8-bit instruction

A

2^4 (four bits in opcode)

18
Q

when is the harvard architecture used

A
  • in microcontrollers
  • microprocessors
  • embedded devices, eg embedded digital signal processing, traffic lights, navigation systems
19
Q

differences between von numann and harvard

A
  • Harvard uses separate buses, Neumann uses combined buses
20
Q

why might Harvard architecture be more preferred over Von

A
  • instruction and data can be accessed simultaneously
  • avoids possibility of data being executed as code
  • ## program cannot be accidentally overwritten
21
Q

difference between direct and intermediate addressing

A

direct addressing means that the operand is the address number whereas intermediate addressing means the operand is the datum

22
Q

Explain why the data bus in a computer system must be bidirectional.

A
  • When data is fetched they have to be transferred from memory to
    the processor
  • data may need to be transferred back to memory
23
Q

if the data bus is 8 bits wide, how long is each instruction

A

16

24
Q

if the address bus is 8 characters long, what is the max address it can transmit

A

255 (2^8)-1

25
Q

what is an instruction set

A

all the instructions which are supported by a processors hardware

26
Q

why might compiles code not run on a computer with a certain processor

A
  • different processors have different instruction sets
  • and the program makes use of the instructions
27
Q

what does the addressing mode do

A

indicates how the value in the operand should be interpreted
- indicates if the value in the operand is a memory address or a data value

28
Q

Describe what an interrupt is and explain the purpose of interrupts

A
  • A signal sent to the processor
  • So that a device that needs the (immediate) attention of the processor can be serviced