CPU Informations: Instructions Processing

CPU Informations:

 
 

Introduction:

To have increasingly fast processors we should increase the frequency, or optimize the circuits already existing, or add a new calculating unit. But if the frequency is increased the production of heat increases too.
This heat can be very dangerous if it exceeds 60 degrees Celsius (electromigration...).
Therefore the engineers seek without stop of new techniques to reduce the size of the processors.
It is necessary to use the capacities of the CPU as well as possible in order not to have to add calculating units.

Procedure:

The first phase is the reading of the instruction in internal memory and is called: theLecture Instruction stage (A).
Then, this instruction must be analyzed in the controller of the processor, it is the Décodage Instruction stage (b),
the following stage relates to the execution of the instruction: execution stage (c).
The last stage relates to the recovery of the result of the operations: stage of arrangement of the operations (d) .

Each stage takes a cycle to be carried out. Thus the fastest instructions are carried out in 4 cycles.
But certain instructions require several cycles at the same time (C).

Comparisons:

Examples:   (pentium)
8 bits Division (unsigned) 15 cycles
16 bits Division (unsigned) 25 cycles
32 bits Division (unsigned) 41 cycles
This information is general, makes a pentium of it has 5 stages for the integer and 8 stages for the floating point.
Each processor has its own characteristics.
Each calculating unit (ALU and FPU) thus have their own stages, less there are stages and more calculation will be fast.

Examples:
iPentium 60 Mhrz Division 16 bits 15cycles 
2.E-4 ms
iPentium 60 Mhrz Division 32 bits 25cycles 
4.17E-4 ms
iPentium 200 Mhrz Division 16 bits 15cycles 
7E-5 ms
iPentium 200 Mhrz Division 32 bits 25cycles 
1.2E-4 ms
The computing speed is thus proportional to the computing speed. But there is another significant point: the number of stages.
 
number of stages: ALU FPU
i Pentium 5 8
i Pentium Pro 14 16
Power PC 4 6
The pentium pro is a processor which must convert the instructions to carry out them (CISC-RISC). It thus has a very great number of stages, but as it is very fast during calculation it exceeds Pentium.