Transcript This is the “classic” diagram of a Central Processing Unit. It is not

D75P 34 – HNC Computer
Architecture
Week 1
Main Components Of A Processor
© C Nyssen/Aberdeen College 2003
All images © C Nyssen /Aberdeen College unless otherwise stated
Prepared 2/9/03
In this lecture we will examine the various components
of the Central Processing Unit (CPU).
This is the “classic” diagram of a CPU.
It is not based on any particular model, but most will
have these seven components.
The CPU contains of a number of registers.
A register is an area for storing information in a binary
format. They are typically made of tiny capacitors (a
component capable of holding an electrical charge).
Capacitors can be either charged (1) or discharged (0)
allowing the storage of binary values.
Various types of capacitor, used for different purposes. An old name for a capacitor
is a condenser.
The Control Unit.
An average,
modern Control
Unit uses about 27
million transistors
and capacitors.
It will also contain
a Decoder unit and
the System Clock.
The clock is a tiny crystal of
pure silicon, with an
electrical current passed
across it. This makes it
oscillate at very high speeds
- in a 1 GHz processor it will
vibrate 1,000,000,000 times
per second.
The decoder consists of transistors and capacitors.
When it receives a program instruction, it interprets
the binary code.
The CU needs a “workspace” where it can decode any
instructions it receives.
This is called the Instruction Register.
Whenever a program is about to be run, the binary code
is first loaded into the RAM (Random Access Memory).
The CU then “imports” it’s instructions from the RAM.
But the CPU needs to know from which address in the
RAM - the Memory Address Register points to the right
one.
But how does the MAR know where to point?
(Sometimes) the Program Counter tells it.
The Program Counter also keeps track of what point in
the program we have reached.
The data and instructions may only enter or leave the
CPU by one “portal” or buffer.
This is the Memory Data (Memory Buffer) Register.
When performing calculations or Boolean logic, data is
sent to the Arithmetic and Logic Unit.
The ALU also consists of capacitors and transistors. It
is usually depicted as a “V” shape in diagrams.
Like the CU, the ALU needs a “workspace” to
manipulate values.
This is called the Accumulator.
The seven components shown are essential to the
CPU. Different models will have many, more
registers in addition to those shown here.
Summary
The CPU contains a number of registers. These consist of
capacitors and transistors.
The CU is the overall controller. It decodes instructions held
in the IR. It also contains the system clock.
The PC and MAR are pointer registers. They keep track of
where the program has reached and which RAM cell is being
currently addressed.
The MDR acts as a point of entry/exit to/from the CPU.
The ALU performs arithmetic and logic operations. It
manipulates data in the Acc.