Summary notes of GCSE OCR computing - topic: System Architecture

System Architecture

Purpose ofthe CPK

·
The the CPI to data and instructions
purpose of is
process
Itis the
where all
searching, sorting, calculating and decision

making takes place in the
computer

The CPU will issue instructions devices
·


to other depending
the the
results
processing
on of




FDE Cycle Stages of FDE Cycl

Fetch Fetch


·
·
The value in PC is spied to the
Execute Decode MAR the
I
using address in the

MAR data/instructions are fetched
from main memory and stored in

te MDR

·
PC is incremented


Decode
scecute
E

The Instruction MDR
·

in the is

The Instruction
·
decoded the is
by control unit into
performed.
Ifthe
an
operator and
operand instruction involves a


calculation then
or
logic operation
the arithmetic unitis
logic
FDE Cycle Registers responsible for this
-




·
The Resultis stored in the

Program Counter PC accumulator


stores the
·

address of next

Memory Data (MDR)
instruction increments By I each
Register
loop of the FDE cycle
·
Holds the data/instruction
which nas been fetched
Memory Address
Register (MAR) from main memory

·
Stores the address ofthe Accumulator (ACC)
instruction to be fetched or

Holds the
·

written intermediate results
from calculation after decoding
and execution