1.1 - Systems Architecture Flashcards
What is the purpose of CPU?
- To process data
- A place where processes like, sorting, searching & calculating take place
What are the three stages of the fetch-execute cycle?
Fetch
Decode
Execute
What happens at each stage of the fetch-execute cycle?
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
What is the CPU?
- Central processing unit
- Decodes and executes instructions
What are the four main components of CPU?
- Arithmetic Logic Unit (ALU)
- Control Unit (CU)
- Cache
- Registers
What is the function of the ALU?
- Carrying out arithmetic calculations
- Making logical decisions
- Handles bit shifting
What is the function of the CU?
- To send signals to control how data moves around the CPU
- Decodes instructions
What is the function of Cache?
- To provide fast access to frequently used instructions and data
What are Registers?
- Tiny, super fast pieces of onboard memory inside the CPU, each with a very specific purpose
- Enables FDE Cycle
What is the Von Neumann Architecture?
- Based on the stored program concept
- Instructions and data share the same memory space
- Instructions are fetched, decoded and executed one at a time
What does the VNA consist of?
- Control Unit (CU)
- Arithmetic Logic Unit (ALU)
- Main Memory (RAM)
- Inputs and Outputs
What registers does a VN CPU contain?
- Program Counter (PC)
- Memory Address Register (MAR)
- Memory Data Register (MDR)
- Accumulator
What is the function of a PC?
PC:
- Holds address of next instruction to be executed in memory
What is the function of an Accumulator?
Accumulator:
- Holds the results of calculations
- Used to hold the data currently being processed by the central processor
What is the function of MAR?
- Assists the FDE cycle
MAR: - Holds the memory address where data is to be fetched from or written to (currently being accessed)
What is the function of MDR?
- Assists the FDE cycle
MDR: - Holds data fetched from memory or to be written to memory
What is the difference between storing data and an address?
- 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
What are the 3 main characteristics that affect CPU performance?
- Clock speed
- Cache size
- Number of cores
What is Clock Speed?
- 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
What is Cache?
- 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
What is Cache Size?
- 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
What are Cores?
- 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
What happens if you double the amount of cores you have?
- 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
What happens to each of the characteristics if you change them?
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
What are embedded systems?
- A computer system with a dedicated function within a larger mechanical system
What are the typical properties of an embedded system?
- Low power consumption
- Small size
- Rugged operating ranges
- Low cost per unit
What are some examples of embedded systems?
- Traffic lights
- House appliances
- Factory equipment
- Engine management systems
- Hospital equipment
