Processors, I/O and storages devices

Question 1

Describe the fetch stage of the FDE cycle

Answer 1

-Contents of PC copied from PC to MAR
-Address is sent along address bus
-Control unit sends a read signal to main memory along control bus
-Content stored in memory address copied to MDR (sent along data bus)
-PC incremented to next instruction
-Contents of MDR copied to CIR

Question 2

Describe the decode stage of the FDE cycle

Answer 2

-Instruction held in CIR is decoded by the CU, split into opcode and operand
-Opcode determines type of instruction and hardware needs
-Operand holds either the address of the data (copied to MAR), the actual data (copied to MDR) or the data to be operated on (copied to ALU/ACC)

Question 3

Describe the execute stage of the FDE cycle

Answer 3

Instruction carried out on the operand

Question 4

What is the function of the control unit?

Answer 4

-Synchronisation of FDE cycle
-Sends control signals to coordinate movement of data through processor
-Controls buses
- Decodes instuctions

Question 5

What are registers and why are they needed?

Answer 5

-Temporary storage/memory location inside the CPU, used for a specific purpose
-Needed because they allow fast access to frequently needed data (1), faster that accessing RAM/secondary storage (1)

Question 6

In what situation may a register value change?

Answer 6

-PC increments during FDE cycle
-Jump instruction from CIR (1), PC changes to address given (1)

Question 7

What is the function of the program counter?

Answer 7

PC stores address of next instruction, sends this to MAR then increments

Question 8

What is the function of the memory address register?

Answer 8

MAR stores the memory location of the data to be fetched

Question 9

What is the function of the memory data register?

Answer 9

-MDR stores the data from memory location specified by MAR
-Acts as buffer

Question 10

What is the function of the address bus?

Answer 10

Carries the address of the memory location being read from or written to.

(Address bus transfers the memory location to access the data)

Question 11

What is the function of the data bus?

Answer 11

Carries data between the processor and memory

(Data bus transfers the data from the memory location specified by MAR)

Question 12

What is the function of the control bus?

Answer 12

Control bus transmits control signals from the control unit

Question 13

What is the function of the accumulator (at least 5)?

Answer 13

-Holds all input/output
-Holds results of calculations (from the ALU)
-Checked for conditional branching (e.g. BRZ)
-Stores data which has come from the MDR/RAM
-Temporary storage for data being processed / during calculations
-I/O in processor, used as buffer

Question 14

What is a GPU?

Answer 14

-Specialised electronic circuit for graphics
-Has parallel structure
-Thousands of small but efficient cores
-Can process huge blocks of visual data simultaneously
-However, CPU is general purpose
-SIMD device (Single Instruction, multiple data)

Question 15

What is meant by CISC?

Answer 15

-Complex instruction set computer
-Each instruction may take multiple cycles
-Single register set
-Many instructions available
-Complicated processor design
-Integrated circuit is expensive

Question 16

What is meant by RISC?

Answer 16

-Reduced instruction set computer
-Each instruction performs a single task
-Limited number of instructions available
-Complex tasks can only be performed by combining multiple instructions
-Simple processor design (less transistors)

Question 17

Explain one advantage of RISC over CISC

Answer 17

Programs run faster (1) due to simpler instructions (1)

Question 18

What is meant by a coprocessor?

Answer 18

-Does floating point arithmetic
-Can do calculations
-So processing is faster

Question 19

What are the characteristics of Von Neumann architecture?

Answer 19

-Instructions executed in linear sequence
-Single control unit
-One instruction at a time
-FDE cycle
-Instructions and data stored together / in the same format

Question 20

What is meant by array processing?

Answer 20

-Single instruction multiple data (SIMD)
-Allows same instruction to operate simultaneously on multiple locations / many ALU’s

Question 21

What is pipelining and how does it improve performance?

Answer 21

-Concurrent processing of multiple instructions
-One instruction can be fetched whilst the previous one is being decoded…
-…and the one before is being executed.
-In case of a branch pipeline is flushed
-Increases throughput
-Prevents idle components

Question 22

What are the characteristics of Harvard architecture?

Answer 22

-Uses separate memory blocks for instructions and data
-Has separate buses (data and address) for data and instructions
-Has fixed memory sizes for data and instructions
-Instruction memory may be ROM
-Can read/write data and instructions
simultaneously (2024 MS)

Question 23

How does a magnetic hard drive work?

Answer 23

Works by magnetic patterns being read off platters that mechanically spin at high speeds

Question 24

Explain a disadvantage of a magnetic hard drive

Answer 24

-Not very portable, as it is susceptible to damage if moved quickly/suddenly due to head coming in contact with platter

Question 25

How does a solid state drive work?

Answer 25

They use memory chips, which can have contents erased and subsequently overwritten when electrical charge is applied

Question 26

Explain an advantage of a solid state drive

Answer 26

-No moving parts, so can be compact -Silent, so lower power consumption

Question 27

How does optical media work?

Answer 27

-Read / written to, using a laser -Read / written onto a reflective surface -Data is stored using pits and lands -E.g. Blu-Ray / CD

Question 28

State the advantages of optical media

Answer 28

– Cheap to produce / buy – Capacity big enough to hold film – Robust enough to be used over long periods / moved around – Portable – Does not need an internet connection

Question 29

What is meant by RAM?

Answer 29

-Random Access Memory -A form of primary memory -Used to hold data and / or programs in use (active/running data) -Volatile / Loses its contents when power is lost

Question 30

What needs to be stored in RAM?

Answer 30

-Software / user files need to be stored in RAM to offer direct access and allow use to alter contents of files, fast read/write speeds

Question 31

How does adding RAM improve performance?

Answer 31

-Reduces reliance on VM, and RAM is faster to access than VM, and it prevents disk thrashing

Question 32

What is meant by ROM?

Answer 32

-Read only memory -Volatile -Stores boot program (bootstrap loader) -Quick to start up

Question 33

What are some uses of ROM in embedded systems?

Answer 33

-Storing OS as it doesn’t need to be updated, so it is quicker to access -May store instructions (*extracted from Harvard architecture mark scheme*) -Storing encryption keys that cannot be changed -Used as primary/secondary storage

Question 34

What is BIOS and what does it do?

Answer 34

-Basic input/output system -Contains the computer start-up instructions -Loads settings/configuration (CMOS) -Checks hardware devices are available / carries out POST (power-on self-test) check -…and reports errors -Determines the drive on which OS is stored -Loads the bootstrap / OS (into main memory)

Question 35

What is meant by virtual storage, state its advantages?

Answer 35

-Virtual storage is storage that appears to the user as local, but is actually stored on remote servers and accessed via the internet, such as in cloud storage solutions (CHAT GPT) -Can be accessed from elsewhere / other machines -Storage can be expanded as necessary//no limit on size -No on site maintenance required -Allows more local storage capacity for data