1.2 The CPU Flashcards
CPU stands for
Central
Processing
Unit
Importance and use of CPU
Process all the data and instructions that make the system work
CPU has three main parts those being
The control unit
The arithmetic logic unit
The cache
What is the control and what is the use of it
Overall control of the CPU
Executes programs by following the FDE cycle
Controls the flow of data inside the CPU (registers, ALU, cache) and outside (main memory and input/output devices)
What does ALU stand for
Arithmetic
Logic
Unit
What is the ALU and it’s uses
Preforms calculations
Completes simple addition/subtraction/multiplication/division
Compares size of numbers
Logical operations (AND, OR, NOT) and binary shifts
Contains accumulator
What is cache and its use
Very fast memory in CPU (compared to RAM)
Stores regularly used data so CPU can access quickly (CPU checks cache if not there then fetches from RAM)
Low capacity and expensive
The CPU contains varies registers which
They temporarily hold tiny bits of data needed by CPU
Super quick to read/write
What is the Von Neumann design
It describes a system where the CPU runs programs stores in memory
Programs consist of instructions and data which are stored in memory as addresses
What is inside a CPU
3 boxes on the Von Neumann design
Control unit
Registers
ALU
What is inside the control unit and why is this important
The program counter (PC)
This holds the memory address of the instruction for each cycle
What is inside the ALU and why is it important
Accumulator
Stores the results of calculations
What are the 4 processor registers
Pc (program counter)
MAR (Memory Address Register
MDR ( Memory Data Register)
CIR (Current Instruction Register)
What is PC
Hold the location of the next instruction/data address in main memory
What is MAR
Memory address register
The contents of the PC are copied here and then transferred along the address bus
What is MDR
Memory data register
Once data/ instructions are bright from the memory address in main memory they are placed here
What is CIR
Current instruction register
The instructions stores in MDR are copied here
What is a bus
Set of parallel wires connecting two or more independent components of a computer system in order to pass signals between them
What are the three busses
Data bus
Control bus
Address bus
What does the address bus do
Carries addresses from processor to main memory
One direction ( processor generates address)
What does the data bus do
Carries instructions from main memory to the processor
Travel two ways
Data can be read or written
What does the control bus do
Controls signals are sent along the control bus
(E.g memory read or memory write)
Instructs which data will be travelling to/from memory
What is CU
Control unit
Sends control signals between the different internal components
(Memory read/write, HDD)
CPU follows FDE cycle
What does this stand for
Fetch
Decode
Execute
Explain the fetch part of the cycle
Copy address memory from PC to the MAR
Copy the instruction stored in the MAR address to the MDR
Increases the program counter to point to the address of the next instruction, ready for the next cycle
Explain the decode part of the cycle
The instruction in MDR is decided by the CU
The CU may then prepare for the next step
E.g by loading values onto the MAR or MDR
Explain the execute part of the cycle
The instruction is performed
This could be load data from memory,
writes date to memory,
do calculations or logic operation (using ALU),
change address in the PC or halt the program
What are peripherals
Any device not directly connected to CPU
E.g mouse, keyboard, printer, HDD
Devices known as I/O devices (input/output devices) to
What do I/O controllers allow
Allow interface between a hardware device external to the motherboard and the processor itself self
