JEKIE YEAKPEE
06/24/143
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September, 1987

Any discussion of computer architectures, of how computers and computer systems are organized, designed, and implemented, inevitably makes reference to the "von Neumann architecture" as a basis for comparison. And of course this is so, since virtually every electronic computer ever built has been rooted in this architecture. The name applied to it comes from John von Neumann, who as author of two papers in 1945 [Goldstine and von Neumann 1963, von Neumann 1981] and coauthor of a third paper in 1946 [Burks, et al. 1963] was the first to spell out the requirements for a general purpose electronic computer. The 1946 paper, written with Arthur W. Burks and Hermann H. Goldstine, was titled "Preliminary Discussion of the Logical Design of an Electronic Computing Instrument," and the ideas in it were to have a profound impact on the subsequent development of such machines.

Von Neumann's design led eventually to the construction of the EDVAC computer in 1952. However, the first computer of this type to be actually constructed and operated was the Manchester Mark I, designed and built at Manchester University in England [Siewiorek, et al. 1982]. It ran its first program in 1948, executing it out of its 96 word memory. It executed an instruction in 1.2 milliseconds, which must have seemed phenomenal at the time. Using today's popular "MIPS" terminology (millions of instructions per second), it would be rated at .00083 MIPS. By contrast, some current supercomputers are rated at in excess of 1000 MIPS. And yet, these computers, such as the Cray systems and the Control Data Cyber 200 models, are still tied to the von Neumann architecture to a large extent.

Over the years, a number of computers have been claimed to be "non-von Neumann," and many have been at least partially so. More and more emphasis is being put on the necessity for breaking away from this traditional architecture in order to achieve more usable and more productive systems. The expectations for the fifth generation systems seem to require that substantially new architectures be evolved, and that both hardware and software be freed from the limitations of the von Neumann architecture [Sharp 1985].

We all know what the von Neumann architecture is, of course. At least we have strong intuitive feelings about it because this is what we have always used. This is "the way computers work." But to really comprehend what choices there are for computer designers, to appreciate what new choices must be found, it is necessary to have a more definitive understanding of what the von Neumann architecture is and is not and what its implications are.

Von Neumann begins his "Preliminary Discussion" with a broad description of the general-purpose computing machine containing four main "organs." These are identified as relating to arithmetic, memory, control, and connection with the human operator. In other words, the arithmetic logic unit, the control unit, the memory, and the input-output devices that we see in the classical model of what a computer "looks like."

To von Neumann, the key to building a general purpose device was in its ability to store not only its data and the intermediate results of computation, but also to store the instructions, or orders, that brought about the computation. In a special purpose machine the computational procedure could be part of the hardware. In a general purpose one the instructions must be as changeable as the numbers they acted upon. Therefore, why not encode the instructions into numeric form and store instructions and data in the same memory? This frequently is viewed as the principal contribution provided by von Neumann's insight into the nature of what a computer should be.

He then defined the control organ as that which would automatically execute the coded instructions stored in memory. Interestingly he says that the orders and data can reside in the same memory "if the machine can in some fashion distinguish a number from an order" MOORE’S LAW
And yet, there is no distinction between the two in memory. The control counter (what we now usually call the program counter) contains the address of the next instruction, and that word is fetched to be executed. Whatever the control unit "believes" to be an order or to be data is treated as suchMoore’s Law is a computing term which originated around 1970; the simplified version of this law states that processor speeds, or overall processing power for computers will double every two years. A quick check among technicians in different computer companies shows that the term is not very popular but the rule is still accepted.

To break down the law even further, it specifically stated that the number of transistors on an affordable CPU would double every two years (which is essentially the same thing that was stated before) but ‘more transistors’ is more accurate. cpu 2 Moores Law
CPU

If you were to look at processor speeds from the 1970’s to 2009 and then again in 2010, one may think that the law has reached its limit or is nearing the limit. In the 1970’s processor speeds ranged from 740 KHz to 8MHz; notice that the 740 is KHz, which is Kilo Hertz – while the 8 is MHz, which is Mega Hertz.

From 2000 – 2009 there has not really been much of a speed difference as the speeds range from 1.3 GHz to 2.8 GHz, which suggests that the speeds have barely doubled within a 10 year span. This is because we are looking at the speeds and not the number of transistors; in 2000 the number of transistors in the CPU numbered 37.5 million, while in 2009 the number went up to an outstanding 904 million; this is why it is more accurate to apply the law to transistors than to speed.

With all this talk of transistors the average technician or computer user may not understand what the figures mean; a simpler way to explain is that the earlier CPUs on the market had a single speed or frequency rating while the newer models have a rating which refers to more than one CPU. gordon moore 263x300 Moores Law
Gordon E. Moore If you’ve purchased a computer recently you might have an idea of what this means as salespersons may have sold you on the wonders of multi-core CPUs. In the example given above, the speeds over a large number of years went between 1.3 and 2.8, which is barely double but what needs to be kept in mind is that the 2.8 is a QUAD CORE while the 1.3 is a single CORE. This means that the actual power of the 2.8 would be found if you multiply by four – which would give you a whopping 11.2 which is a far cry from 1.3.

Due to the rapid rate that technology has grown in the past few years, most computer technicians you speak with – whether they have heard of Moore’s Law or not will tell you that CPU speeds double each year. Though Moore’s Law had said every two years, this rapid increase in technological production has lessened the period in the minds of technicians and users alike.

The limitation which exists is that once transistors can be created as small as atomic particles, then there will be no more room for growth in the CPU market where speeds are concerned

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