CPU (central processing unit)
Purpose of the CPU - answer The purpose of the CPU is to process data. It is where all
the searching, sorting, calculating and decision making takes place in the computer.
Fetch, decode, execute cycle - answer Fetch:
CPU fetches data and instructions from the main memory and stores it in it's registers.
To do this, the CPU makes use of the the address bus, which fetches the
data/instructions from the address that the CPU has given it. The data/instructions then
moves from the main memory tom the CPU, via the data bus.
Decode:
The next step is for the CPU to make sense of the instruction it has just fetched. The
CPU is designed to understand a specific set of commands. These are called the
'instruction set' of the CPU. Each make of CPU has a different instruction set. The CPU
decodes the instruction and prepares various areas within the chip in readiness of the
next step.
Execute:
This is the part of the cycle when data processing actually takes place. The instruction
is carried out upon the data (executed). The result of this processing is stored in yet
another register. Once the execute stage is complete, the CPU sets itself up to begin
another cycle once more.
The control unit - answerThe Control Unit has three main jobs:
It controls and monitors the hardware attached to the system to make sure that the
commands given to it by the application software are used. For example, if you send
something to print, the control unit will keep a check that the instructions are sent to the
printer correctly. It controls the input and output of data so that the signals go to the right
place at the right time
It controls the flow of data within the CPU - which is the Fetch-Execute cycle described
above.
The immediate access store - answerThis holds the data and programs needed at that
instant by the Control Unit. The CPU reads data and programs kept on the backing
storage and stores them temporarily in the IAS's memory. The CPU needs to do this
because Backing Storage (e.g. the hard disk) is much too slow to be able to run
applications directly. So data and programs are first of all loaded into main memory then
the CPU fetches just the part it immediately needs and loads it into its own internal
registers as part of the Fetch-Execute cycle.
Purpose of the CPU - answer The purpose of the CPU is to process data. It is where all
the searching, sorting, calculating and decision making takes place in the computer.
Fetch, decode, execute cycle - answer Fetch:
CPU fetches data and instructions from the main memory and stores it in it's registers.
To do this, the CPU makes use of the the address bus, which fetches the
data/instructions from the address that the CPU has given it. The data/instructions then
moves from the main memory tom the CPU, via the data bus.
Decode:
The next step is for the CPU to make sense of the instruction it has just fetched. The
CPU is designed to understand a specific set of commands. These are called the
'instruction set' of the CPU. Each make of CPU has a different instruction set. The CPU
decodes the instruction and prepares various areas within the chip in readiness of the
next step.
Execute:
This is the part of the cycle when data processing actually takes place. The instruction
is carried out upon the data (executed). The result of this processing is stored in yet
another register. Once the execute stage is complete, the CPU sets itself up to begin
another cycle once more.
The control unit - answerThe Control Unit has three main jobs:
It controls and monitors the hardware attached to the system to make sure that the
commands given to it by the application software are used. For example, if you send
something to print, the control unit will keep a check that the instructions are sent to the
printer correctly. It controls the input and output of data so that the signals go to the right
place at the right time
It controls the flow of data within the CPU - which is the Fetch-Execute cycle described
above.
The immediate access store - answerThis holds the data and programs needed at that
instant by the Control Unit. The CPU reads data and programs kept on the backing
storage and stores them temporarily in the IAS's memory. The CPU needs to do this
because Backing Storage (e.g. the hard disk) is much too slow to be able to run
applications directly. So data and programs are first of all loaded into main memory then
the CPU fetches just the part it immediately needs and loads it into its own internal
registers as part of the Fetch-Execute cycle.
