Systems architecture Flashcards
Central processing unit (CPU)
The purpose of the CPU is to fetch decode and execute instructions.
FDE cycle
The FDE cycle is the cycle that the CPU runs billions of times per second. A computer takes an input and then delivers the output for the user.
Fetch stage
During the fetch stage of the cycle, the next instruction or data must be fetched from the computers memory (RAM. The instruction or data is brought back to the CPU.
Decode stage
During the decode stage the CPU needs to work out what is required from the instruction.
Execute stage
During the execute stage I the CPU will carry out the instruction that was fetched. For example performing calculations or storing data back in the main memory.
Arithmetic logic unit (ALU)
Performs arithmetic operations and logical decisions.
Control unit (CU)
Coordinates how data moves around the CPU by sending signals to control the flow of the data. It also decodes the instructions fetched from memory.
Cache
Very small, fast memory located in the CPU which is used to provide quick access to frequently used instructions and data.
The more cache there is the more data can be stored which speeds up the performance of the CPU.
It prevents the CPU from having to repeatedly fetch frequently used instructions from RAM.
Registers
Extremely small fast memory located in the CPU. Each register has its own purpose.
It is a temporary storage area built into the CPU.
PC, MAR, MDR, ACC
Von Neumann architecture
The Von Neumann architecture is a design of the CPU. It outlines how the computer memory, input and output devices and processor all work together. The idea that the programme instruction and the data required are both stored in the same memory.
Program counter (PC)
Holds the memory address of the next instruction to be executed. Increments by 1 as the FDE cycle runs.
Memory address register (MAR)
Holds the memory address of the current instruction to be executed and the address of the data to be fetched.
Memory data register (MDR)
Stores the data or actual instruction which has been fetched from memory.
Accumulator (ACC)
Temporarily stores the result of any calculations that have taken place in the ALU.
Clock speed
The clock speed is measured in hertz (Hz) The clock speed measures the number of FDE cycles that take place per second. The faster the clock speed the more instructions can be carried out per second. Modern computers have a clock speed in gigahertz (GHz).
