1.1 - Systems Architecture

Question 1

What is the purpose of CPU?

Answer 1

• To process data
• A place where processes like, sorting, searching & calculating take place

Question 2

What are the three stages of the fetch-execute cycle?

Answer 2

Fetch
Decode
Execute

Question 3

What happens at each stage of the fetch-execute cycle?

Answer 3

Fetch:
- Fetches next instruction from main memory CPU
- Brings instructions back
Decode:
- Inspects instructions, works out what needs to be done
Execute:
- Carries out the instruction

Question 4

What is the CPU?

Answer 4

• Central processing unit
• Decodes and executes instructions

Question 5

What are the four main components of CPU?

Answer 5

• Arithmetic Logic Unit (ALU)
• Control Unit (CU)
• Cache
• Registers

Question 6

What is the function of the ALU?

Answer 6

• Carrying out arithmetic calculations
• Making logical decisions
• Handles bit shifting

Question 7

What is the function of the CU?

Answer 7

• To send signals to control how data moves around the CPU
• Decodes instructions

Question 8

What is the function of Cache?

Answer 8

• To provide fast access to frequently used instructions and data

Question 9

What are Registers?

Answer 9

• Tiny, super fast pieces of onboard memory inside the CPU, each with a very specific purpose
• Enables FDE Cycle

Question 10

What is the Von Neumann Architecture?

Answer 10

• Based on the stored program concept
• Instructions and data share the same memory space
• Instructions are fetched, decoded and executed one at a time

Question 11

What does the VNA consist of?

Answer 11

• Control Unit (CU)
• Arithmetic Logic Unit (ALU)
• Main Memory (RAM)
• Inputs and Outputs

Question 12

What registers does a VN CPU contain?

Answer 12

• Program Counter (PC)
• Memory Address Register (MAR)
• Memory Data Register (MDR)
• Accumulator

Question 13

What is the function of a PC?

Answer 13

PC:
- Holds address of next instruction to be executed in memory

Question 14

What is the function of an Accumulator?

Answer 14

Accumulator:
- Holds the results of calculations
- Used to hold the data currently being processed by the central processor

Question 15

What is the function of MAR?

Answer 15

• Assists the FDE cycle
  MAR:
• Holds the memory address where data is to be fetched from or written to (currently being accessed)

Question 16

What is the function of MDR?

Answer 16

• Assists the FDE cycle
  MDR:
• Holds data fetched from memory or to be written to memory

Question 17

What is the difference between storing data and an address?

Answer 17

• Both instruction & program data are stored in the same memory in binary form
• There is no way to know if the pure binary held in memory represents instructions or data simply by looking at it

Question 18

What are the 3 main characteristics that affect CPU performance?

Answer 18

• Clock speed
• Cache size
• Number of cores

Question 19

What is Clock Speed?

Answer 19

• The number of cycles per second / the frequency at which the internal clock generates pulses
• Measured in Hertz (Hz)
• eg. 3.2GHz clock speed = 3.2 billion instructions fetched per second

Question 20

What is Cache?

Answer 20

• Temporary storage of data and instructions being read to and written from RAM
• Stores copies of recent data and instructions
• Much quicker getting items from cache than RAM
• Tries to avoid getting instructions/data from memory if we don’t need to

Question 21

What is Cache Size?

Answer 21

• The number of instructions / data that can be held within the CPU
• A small cache increases the speed of the CPU because instructions / data are not fetched from RAM

Question 22

What are Cores?

Answer 22

• A processing unit in the CPU
• A complete copy of a CPU
• A quad-core processor would have 4 separate processing units, each with its own Reg, ALU, Accum & CU
• Doubling the number of cores doesn’t double the overall speed

Question 23

What happens if you double the amount of cores you have?

Answer 23

• Doubling the number of cores doesn’t double the overall speed
• CPU cores have to communicate w/ each other, which takes time
• Many programs aren’t designed to make use of multiple cores

Question 24

What happens to each of the characteristics if you change them?

Answer 24

Clock Speed:
- Increase would make the CPU run faster
Cache:
- The bigger the cache, the less time a processor has to wait for instructions to be fetched
Cores:
- System performance will increase if you have more

Question 25

What are embedded systems?

Answer 25

- A computer system with a dedicated function within a larger mechanical system

Question 26

What are the typical properties of an embedded system?

Answer 26

- Low power consumption - Small size - Rugged operating ranges - Low cost per unit

Question 27

What are some examples of embedded systems?

Answer 27

- Traffic lights - House appliances - Factory equipment - Engine management systems - Hospital equipment