1.1 Systems Architecture Flashcards
What is the purpose of the control unit (CU)?
- Co-ordinates all activities of the CPU
- Directs the flow of data between the CPU and other devices
What is the purpose of the program counter (PC)?
- Holds the address of the next instruction to be executed
What is the purpose of the memory address register (MAR)?
- Holds the address of the memory location from which data or an instruction is to be fetched or to which data is to be written
- Sends the address to memory down the address bus
What is the purpose of the memory data register (MDR)?
- Used to temporarily store the data which is read from and written to memory
- All data to and from memory must travel down the data bus and pass through the MDR
What is the purpose of the current instruction register (CIR)?
- Holds the current instruction being executed
- Contains the opcode and operand of the current instruction
What is the purpose of the arithmetic logic unit (ALU)?
- Performs logical and arithmetic operations on data
What is the purpose of the accumulator?
- Holds the results of calculations made in the ALU
What are buses?
- A physical set of parallel wires connecting and carrying groups of bits between several components of a computer
What is an address bus?
- Carries memory address which identify where data is read from or written to
What is a data bus?
- Carries that binary that make up the actual information being transmitted around the CPU
What is a control bus?
- Controls command and control signals to and from every other component of the CPU
What are the factors that affect the performance of the CPU?
- Clock speed
- Cache size
- Number of cores
Factors that affect the performance of the CPU: clock speed
- The number of instruction cycles it can execute per second
- Measured in hertz
Factors that affect the performance of the CPU: cache size
- Holds data and instructions that are frequently accessed and used by the CPU
- Much quicker to access than RAM
Factors that affect the performance of the CPU: number of cores
- A complete copy of the CPU
- CPUs with multiple cores have the power to run multiple programs at the same time
Why does doubling the number of cores not necessarily mean it will double the performance?
- Extra communication is needed between the cores = extra time
- Many programs are not designed to make use of multiple cores
What is pipelining?
- The process of completing the FDE cycles of three separate instructions simultaneously
Von Neumann architecture
- Shared memory space for data and instructions (in the same format)
- A single CU/processor follow a linear FDE cycle
- One instruction at a time
Harvard architecture
- Instructions and data stored in separate memory units (own bus)
- Reading and writing can be done at the same time as fetching an instruction
- Used by RISC processors
Contemporary Processor architecture
- A modern computer architecture combining elements of both Von Neumann and Harvard architecture
What is the the purpose of Single Instruction Multiple Data (SIMD)?
- Parallel processing is where a processor carries out a single instruction on multiple data items at the same time
What is the the purpose of Multiple Instruction Multiple Data (MIMD)?
- Multiple instructions are carried out on multiple data across several cores