How The First Cpu Was Organized—(3)

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How the registers inside CPUwork

In the first von Neumann computer

Each “instruction” written by the human engineer

Was made of forty zeroes and ones.

When the instruction (copy of it) was transmitted

From the main memory to the CPU,

On the forty lane superhighway

It was first received in the “Data Register”

Which had forty flip flop chambers.

And which was a most important register.

But each instruction in that ancient computer

Was actually a combination of two instructions

Of twenty bits each and so the Data Register

Broke the big instruction into two.

It sent the second half to another register

For temporary safekeeping

And processed the first twenty bits forthwith.

The Data register again breaks the first half

Into eight bit and twelve bit parts

The first eight bits indicated the mathematical circuit.

To CPU accordingly switches on that specified circuit

(One of the add/subtract/multiply/divide circuits

Contained in the registers of the ALU).

The twelve bit part of the first half

Indicated the 010101code of “memory house ”

The code is sent to the “memory access register”

A command is sent by CPU to the concerned memory house.

As per command from the CPU

A copy of the 010101 code of the number

Contained in that memory house

Goes to the ALU’s mathematical registers.

The 010101 code of the answer coming from ALU

Again had to travel to the Data Register

And from there to a specified memory house

In the main memory board

Reserved for the answer as per CPU’s order.

Then only the second part of the instruction.

Is taken for processing and it is processed in a similar way.

The first eight bits denote the mathematical circuit .

The remaining twelve bits show the 010101 code

Of the memory house containing the number ‘

The “instructions” bring only the 010101 codes

Of only the “memory houses”

And not of the actual numbers

Contained in those memory houses.

This we should understand in the clearest way.

The “memory access register” helps the CPU

In identifying the memory house as per its code

And helps CPU issue the electric pulse required

To bring that number to the Data Register.

(In the form of its twelve bit 010101 code) .

Another important register in CPU called “Index Register”

Intimates the 010101 code of the memory house

Containing the next instruction

And sends it to the Memory Access Register

This register in turn informs the CPU

To send electric pulse to that memory house

To make it send a copy of the instruction

To the versatile Data Register!

You may feel that all this process is long and tedious

But it takes just a billionth of second for the computer

To process all the forty bit instructions of entire program..

The Main Memory, the CPU and the ALU

All working in close coordination

Can process a million instructions in a second

With out any human intervention

That is the great advantage of the “von Neumann machine “



The CPU sends “question” pulses to all the parts

And wants only “yes/no answer” pulses.

As per the reply pulses given by the parts

The CPU switches the big circuits.

All these question/answer pulses both ways

Form a coded language and are recorded

In a permanent section of main memory

As a permanent reference book.

We may say in a way that it has developed

Into the modern “operating system” or “OS”

We can also view the operating system in another way.

The big doctors can not work in hospital

Without help of compounders and nurses.

The big professors can not work in a university

Without a big group of assistants and clerks.

The big actorscan not act in a studio

Without help of the several helping staff

Similarly the big “Processors”

Inside any big moderncomputer

Can not do the data processing work

Without a powerful “operating system”


In modern “desk top computers”

The big dictionary-like operating system

Is recorded in “hard disc” by the manufacturer.

When computer is switched on

The main memory comes alive

And a copy of the OS flows on to it from hard disc

And remains live and active

Till the machine is switched off..

Dr von Neumann clearly defined

The complicated switching duties of CPU .

The CPU is responsible

For ensuring correct functioning of all circuits

And so checks all circuits periodically.

It has also a fixed written list of “microinstructions”

Relating to each standard instruction.

It has to do all switching based only on this list.

The OS which is a part of the CPU

Fixes priorities for use of CPU and ALU

By the other computer parts

(Like the main memory and the input and output devices)..

Such routine duties overburden the main CPU.

So a section of the CPU is developed as the OS

As separate commander to attend to such duties.

Only when the automatic

And self-loading MSDOS

(“Microsoft Disc Operating System”)

Popularized by the legendary Bill Gates

Became available to the common man,

The small “von Neumann machines”

Which we call as the “desk tops computers”

Became popular worldwide and were sold in millions.

They are the common “computers”

Which has become now as common

As the TV, radio and the telephone..


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