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32 CHAPTER 2 / COMPUTER EVOLUTION AND PERFORMANCE
1 billion
transistor CPU
10 9
10 8 7
Transistors per chip 10 6
10
10 5
10 4
10 3
1970 1980 1990 2000 2010
Figure 2.8 Growth in CPU Transistor Count [BOHR03]
was necessary to break out of some of the constraints of the 7000 architecture and to
produce a system capable of evolving with the new integrated circuit technology
[PADE81, GIFF87]. The strategy paid off both financially and technically. The 360
was the success of the decade and cemented IBM as the overwhelmingly dominant
computer vendor, with a market share above 70%.And, with some modifications and
extensions, the architecture of the 360 remains to this day the architecture of IBM’s
6
mainframe computers. Examples using this architecture can be found throughout
this text.
The System/360 was the industry’s first planned family of computers.The fam-
ily covered a wide range of performance and cost. Table 2.4 indicates some of the
key characteristics of the various models in 1965 (each member of the family is dis-
tinguished by a model number). The models were compatible in the sense that a
program written for one model should be capable of being executed by another
model in the series, with only a difference in the time it takes to execute.
The concept of a family of compatible computers was both novel and ex-
tremely successful. A customer with modest requirements and a budget to match
could start with the relatively inexpensive Model 30. Later, if the customer’s needs
grew, it was possible to upgrade to a faster machine with more memory without
6 The term mainframe is used for the larger, most powerful computers other than supercomputers.Typical
characteristics of a mainframe are that it supports a large database, has elaborate I/O hardware, and is
used in a central data processing facility.
