1945 AD
Von Neumann writes the "First Draft"
In June 1944, the Hungarian- American mathematician Johann (John) Von Neumann
first became aware of ENIAC.
Von Neumann, who was a consultant on the Manhattan Project, immediately recognized the role that could be played by a computer like ENIAC in solving the vast arrays of complex equations involved in designing atomic weapons.
John von Neumann
Copyright (c) 1997. Maxfield & Montrose Interactive Inc.
A brilliant mathematician, Von Neumann crossed mathematics with subjects such as philosophy in ways that had never previously been conceived; for example, he was a pioneer of Game Theory, which continues to find numerous and diverse applications to this day.
Von Neumann was tremendously excited by ENIAC and quickly became a consultant to both the ENIAC and EDVAC projects. In June 1945, he published a paper entitled "First Draft of a report to the EDVAC," in which he presented all of the basic elements of a stored-program computer:
1.
A memory containing both data and instructions. Also to allow both data and
instruction memory locations to be read from, and written to, in any desired
order.
2.
A calculating unit capable of performing both arithmetic and
logical operations on the data.
A control unit, which could interpret an instruction retrieved from the memory and select alternative courses of action based on the results of previous operations.
The key point made by the paper was that the computer could modify its own programs, in much the same way as was originally suggested by Charles Babbage for his Analytical Engine. The computer structure resulting from the criteria presented in the "First Draft" is popularly known as a von Neumann Machine, and virtually all digital computers from that time forward have been based on this architecture.
The "First Draft" was a brilliant summation of the concepts involved in stored-program computing; indeed, many believe it to be one of the most important documents in the history of computing. It is said that the paper was written in a way that possibly only von Neumann could have achieved at that time.
However, although there is no doubt that von Neumann made major contributions to the EDVAC design, the result of the "First Draft" was that he received almost all of the credit for the concept of stored-program computing, while Mauchly and Eckert received almost none. But Mauchly and Eckert discussed stored-program computers a year before von Neumann arrived on the scene, and Eckert wrote a memo on the subject six months before von Neumann had even heard about ENIAC.
It has to be said that there is no evidence that Von Neumann intended to
take all of the credit for EDVAC and the stored program computing concept (not
the least that his paper was titled "First Draft ...."), but
it also cannot be denied that he didn't go out of his way to correct matters
later.
These
notes are abstracted from the book Bebop BYTES Back
(An Unconventional Guide to Computers) Copyright Information
Harvard
architecture
From
Wikipedia, the free encyclopedia.
The term Harvard
architecture originally referred to computer architectures that used separate data
storage for their instructions and data (in contrast to the Von Neumann architecture). The term
originated from the Harvard Mark I relay based computer, which stored
instructions on punched tape and data in relay latches.
The term Harvard
architecture is usually used now to refer to a particular computer architecture design philosophy where
separate data paths exist for the transfer of instructions and data.
All computers
consist primary of two parts, the CPU which processes data, and the memory which holds
the data. The memory in turn has two aspects to it, the data itself, and the
location where it is found - known as the address. Both are important to the
CPU, as many common instructions boil down to something like "take the
data in this address and add it to the data in that address", without
actually knowing what the data itself is.
In recent years the
speed of the CPU has grown many times in comparison to the memory it talks to,
so care needs to be taken to reduce the numbers of times you access it in order
to keep performance. If, for instance, every instruction run in the CPU
requires an access to memory, the computer gains nothing for increased CPU
speed - a problem referred to as being memory bound.
Memory can be made
much faster, but only at high cost. The solution then is to provide a small
amount of very fast memory known as a cache. As long as
the memory the CPU needs is in the cache, the performance hit is very much less
than it is if the cache then has to turn around and get the data from the main
memory. Tuning the cache is an important aspect of computer design.
The Harvard
architecture refers to one particular solution to this problem. Instructions
and data are stored in separate caches to improve performance. However this has
the disadvantage of halving the amount of cache available to either one, so it
works best only if the CPU reads instructions and data at about the same
frequency.
Von Neumann architecture
From
Wikipedia, the free encyclopedia.
Von Neumann architecture refers to computer architectures that use the same data
storage for their instructions and data (in contrast to the Harvard architecture). The term originated
from First Draft of a Report on the EDVAC (1945), a paper written
by the famous mathematician John
von Neumann, that proposed the stored program concept. The paper was
written in connection with plans for a successor machine to the ENIAC and its
concepts were discussed by J.
Presper Eckert, John Mauchly, Arthur Burks, and others over a period of several
months prior to Von Neumann writing the draft report.
A
von Neumann Architecture computer has five parts: an arithmetic-logic unit, a
control
unit, a memory, some form of input/output and a bus
that provides a data path between these parts.
A
von Neumann Architecture computer performs or emulates the following sequence
of steps:
1.
Fetch the next instruction from memory at the address in the
program counter.
2.
Add 1 to the program counter.
3.
Decode the instruction using the control unit. The control
unit commands the rest of the computer to perform some operation. The
instruction may change the address in the program counter, permitting
repetitive operations. The instruction may also change the program counter only
if some arithmetic condition is true, giving the effect of a decision, which
can be calculated to any degree of complexity by the preceding arithmetic and
logic.
4.
Go back to step 1.
Very
few computers have a pure von Neumann architecture. Most computers add another
step to check for interrupts, electronic events that could occur at any time.
An interrupt resembles the ring of a telephone, calling a person away from some
lengthy task. Interrupts let a computer do other things while it waits for
events.
Von
Neumann computers spend a lot of time moving data to and from the memory, and
this slows the computer (this problem is called von Neumann bottleneck ) so, engineers often
separate the bus into two or more busses, usually one for instructions, and the
other for data.