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26 CHAPTER 2 / COMPUTER EVOLUTION AND PERFORMANCE

Table 2.2 Computer Generations

Approximate Typical Speed
Generation Dates Technology (operations per second)

1 1946–1957 Vacuum tube 40,000
2 1958–1964 Transistor 200,000
3 1965–1971 Small and medium scale 1,000,000
integration
4 1972–1977 Large scale integration 10,000,000
5 1978–1991 Very large scale integration 100,000,000
6 1991– Ultra large scale integration 1,000,000,000

company to deliver the new technology. NCR and, more successfully, RCA were the
front-runners with some small transistor machines. IBM followed shortly with the
7000 series.
The use of the transistor defines the second generation of computers. It has be-
come widely accepted to classify computers into generations based on the fundamen-
tal hardware technology employed (Table 2.2). Each new generation is characterized
by greater processing performance, larger memory capacity, and smaller size than the
previous one.
But there are other changes as well. The second generation saw the introduc-
tion of more complex arithmetic and logic units and control units, the use of high-
level programming languages, and the provision of system software with the
computer.
The second generation is noteworthy also for the appearance of the Digital
Equipment Corporation (DEC). DEC was founded in 1957 and, in that year, deliv-
ered its first computer, the PDP-1.This computer and this company began the mini-
computer phenomenon that would become so prominent in the third generation.

THE IBM 7094 From the introduction of the 700 series in 1952 to the introduction
of the last member of the 7000 series in 1964, this IBM product line underwent an
evolution that is typical of computer products. Successive members of the product
line show increased performance, increased capacity, and/or lower cost.
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Table 2.3 illustrates this trend.The size of main memory, in multiples of 2 36-bit
4
words, grew from 2K (1K = 2 ) to 32K words, while the time to access one word of
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memory, the memory cycle time, fell from 30 s to 1.4 s. The number of opcodesmm
grew from a modest 24 to 185.
The final column indicates the relative execution speed of the central process-
ing unit (CPU). Speed improvements are achieved by improved electronics (e.g., a
transistor implementation is faster than a vacuum tube implementation) and more
complex circuitry. For example, the IBM 7094 includes an Instruction Backup Reg-
ister, used to buffer the next instruction.The control unit fetches two adjacent words

4 A discussion of the uses of numerical prefixes, such as kilo and giga, is contained in a supporting docu-
ment at the Computer Science Student Resource Site at WilliamStallings.com/StudentSupport.html.