Structure And Function Of Processor

Question 1

What does the ALU do?

Answer 1

Performs calculations by receiving Opcodes and Operands. Executes instruction on opcode and outputs result to storage register

Question 2

What components make up a modern processor?

Answer 2

CU, ALU and Registers

Question 3

What are the types of registers?

Answer 3

• MAR
• MDR
• PC
• ACC
• CIR

Question 4

What does the program counter do?

Answer 4

• Contains address of the next instruction to be executed

- Increments when one instruction is read

Question 5

What does the Accumulator Do?

Answer 5

• Stores result of executions temporarily before being transferred to the memory?
• Hold INP/out data currently being processed

Question 6

What is the purpose of the Memory Address register?

Answer 6

• Stores address of memory location currently in use
• Allows communication with address bus
• Output goes to address bus

Question 7

What is they purpose of the MDR?

Answer 7

• Stores data/instructions fetched from memory before use by processor
• Buffer between CPU and memory unit. Makes it so data is written in one big go to the memory instead of writing the data individually. It makes it faster as you are only doing the slow write operation once rather than multiple times
• Allows CPU to communicate with data bus

Question 8

What is the purpose of CIR?

Answer 8

Stores current instruction to be executed

Question 9

What are the types of buses and what do they do?

Answer 9

• Control bus = Used to communicate with other devices and components, carrying commands rom CPU + returning status signals
• Data bus = carries information
• Address bus = Carries memory address of data

Question 10

What does the CU do?

Answer 10

• Sends signals around the processor
• determines how data is transferred between memory-CPU and between components of CPU.
• Decodes instructions
• clock is located in the CU

Question 11

What is cache Memory?

Answer 11

Small amount of RAM built into CPU. Stores info the CPU is most likely to need next. Faster than accessing RAM. Up to three levels (L1-L3 with L1 being smallest but fastest)

Question 12

What is the clock rate?

Answer 12

• Determines how fast instructions are executed
• Each ‘tick’ begins when clock switches from 0 to 1
• Ticks are directly proportional to speed
• Measured in MHz or GHz

Question 13

What happens up in the fetch stage of the cycle?

Answer 13

-PC holds address of next instruction
-This address is copied to the MAR
-The contents of the address in the MAR are copied to the MDR
-contents of MDR copied to CIR
-PC is Incremented and process repeats
LOOK IN PHOTOS FOR DIAGRAM

Question 14

What happens in the decode part of the cycle?

Answer 14

• CU works out what instruction does
• Checks against a set of instructions held in ROM
• Each instruction had microcode
• Microcode provides a step by step guide on how to perform instruction
• Checks all necessary data is present
• Pass instruction and data to schedule

Question 15

What happens in the schedule part of the cycle?

Answer 15

• Decides which execute unit to send instruction to
• Depends what type of instruction as to what one it’s passed to
• Passes to execution

Question 16

What happens in the execute part of the cycle?

Answer 16

• Possibly several execution units working at once in parallel
• Different types of execution units for different types of instruction: Floating point, Arithmetic unit, logic unit
• Returns result from L1
• Result sent to RAM/other appropriate location

Question 17

What is pipelining?

Answer 17

• while one instruction is being executed the next is being decoded and the one after that is being fetched.
• not always possible to accurately predict what instruction needs to be fetched and decoded next

Question 18

What does it mean to “flush out the pipes”?

Answer 18

• an instruction, when executed, might branch to a different, random instruction. (Eg instruction 2 being executed results in branching to instruction 9)
• flushing the pipes means removing existing instructions. So the instructions currently in the decode and fetch stage will be removed. Eg: four will be removed from fetch and three will be removed from decode

Question 19

What is a GPU?

Answer 19

• specially designed processor to perform calculations with graphics
• have instruction sets specially designed for the sorts of calculations required in graphics processing
• use Single instruction multiple data (SIMD) because the same calculations often need to be carried out across multiple points on the screen
• graphics cards contain fast GPU’s with their own memory
• day to day PC’s will have GPU’s embedded onto the main processor

Question 20

What are GPU’s used for?

Answer 20

• modelling physical systems
• audio processing
• breaking passwords
• machine learning
• gaming
• rendering