Dr Von Neumann's Computer—-(3)

But how can a lifeless part CPU do the work

Dr von Neumann devised an entire world

Of almost magical computer architecture and working plan.

For this purpose he kept many special purpose registers

Inside each processor like alu and CPU.

One register could divide

Forty bit long 010101 strings into smaller specified pieces

And send to smaller registers specially made for them.

One register could decode the binary code

Relating to electric circuits

So that CPU could issue necessary electric signals.

The DR register made of forty chambers

Is actually two registers of twenty chambers each

Each twenty bit register is divided

Into still smaller registers

Of eight bit and twelve bit parts

Thus the DR takes in the forty bit instruction

Coming from the main memory board

In the special forty bit super highway

The DR divides the forty bit instruction

Into two twenty bit parts.

First group of twenty bits are retained

And the second group of twenty bits

Automatically flows to another register called IBR.

The IBR is a temporary store (it is a “buffer”.)

The first group of twenty bits is again cut into two parts

First eight bits is a code to switch on

The special electric circuit in ALU

To “add/subtract/multiply/ divide”

The remaining twelve bits is the address

Of the particular memory house

In which thenumber

To be added/subtracted

Or to be multiplied or divided

Is resting for a little billionth of a second.

Remember here one of the foremost rules

Of the von Neumann machine

The registers mention

Only the name of the memory houses

Where numbers are resting

They do not contain the number!

The eight bit code of the mathematical circuit

Is sent to the CPU the chief switching expert.

The CPU sends electric signals

Which immediately switch on that circuit in the ALU

The twelve bit part is the address (in 010101code)

Of the memory house in the main memory board

In which the number on which

The “add/subtract/multiply/ divide”

Is to be done and which is resting

In the memory house.

Only this address of the memory house is sent to

The register called IR (which works inside cpu)

The very important duty of IR

Is to link these “house names” like X, Y, Z

Given by the human engineer with the “house numbers”

Allotted by the manufacturer of the computer

To the “memory houses” of the Main Memory.

(In modern computers the main memory board

Is a mega city with millions of memory houses,

Built from millions of submicroscopic transistors

In a shirt button size silicon chip.

But in the ancient computers of 1940s

There were perhaps only a few hundred memory houses

On the magnetic main memory board!)

If the register IR supplies that” house number”.

Another register called Memory Address Register (MAR)

Directly points the direct electrical path

To that particular memory house, you may say.

To that memory house pointed out by MAR

The CPU sends the prescribed standard electric signals.

Then automatically and instantly

The 010101 binary code

Of that number contained in that memory house

Travels through one of the computer’s super highways

Into the register DR (already familiar to us.)

DR in turn forwards that binary code of the number

To the“accumulator” register inside the ALU.

(About the “accumulator” register

Which exists inside the alu we already know.

It is like a water drum into which

Water using a standard measuring jar

Is poured and poured and level goes on increasing.

Or water is removed with the same measuring jar

And level decreases accordingly.

The accumulator drum always shows the current level).

Into “accumulator register” of ALU

Numbers are “poured in” or “poured out”

And the register shows current answer worked out in ALU.

The wonder is that all this action is over

In a billionth of a second

And answers start flowing out in to other

Identified memory houses on main memory board

Awaiting orders of CPU.



Are fully implemented

And final answer is finally worked out