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Definition
Over the past four decades the computer industry has experienced four generations
of development, physically marked by the rapid changing of building blocks from
relays and vacuum tubes (1940-1950s) to discrete diodes and transistors (1950-1960s),
to small- and medium-scale integrated (SSI/MSI) circuits (1960-1970s), and to
large- and very-large-scale integrated (LSI/VLSI) devices (1970s and beyond).
Increases in device speed and reliability and reductions in hardware cost and
physical size have greatly enhanced computer performance. However, better devices
are not the sole factor contributing to high performance. Ever since the stored-program
concept of von Neumann, the computer has been recognized as more than just a hardware
organization problem. A modern computer system is really a composite of such items
as processors, memories, functional units, interconnection networks, compilers,
operating systems, peripherals devices, communication channels, and database banks. To
design a powerful and cost-effective computer system and to devise efficient programs
to solve a computational problem, one must understand the underlying hardware
and software system structures and the computing algorithm to be implemented on
the machine with some user-oriented programming languages. These disciplines constitute
the technical scope of computer architecture. Computer architecture is really
a system concept integrating hardware, software algorithms, and languages to perform
large computations. A good computer architect should master all these disciplines.
It is the revolutionary advances in integrated circuits and system architecture
that have contributed most to the significant improvement of computer performance
during the past 40 years. In this section, we review the generations of computer
systems and indicate the general tends in the development of high performance
computers.
Generation of Computer Systems
The division of computer systems into generations is determined by the device
technology, system architecture, processing mode, and languages used. We consider
each
generation to have a time span of about 10 years. Adjacent generations
may overlap in several years as demonstrated in the figure. The long time span
is intended to cover both development and use of the machines in various parts
of the world. We are currently in the fourth generation, while the fifth generation
is not materialized yet.
The Future
Computers to be used in the 1990s
may be the next generation. Very large-scale integrated (VLSI) chips will be used
along with high-density modular design. Multiprocessors like the 16 processors
in the S-1 project at Lawrence Livermore National Laboratory and in the Denelcor's
HEP will be required. Cray-2 is expected to have four processors, to be delivered
in 1985. More than 1000 mega float-point operations per second (megaflops) are
expected in these future supercomputers.
Need
For Parallel Processing
Achieving high performance
depends not only on using faster and more reliable hardware devices, but also
on major improvements in computer architecture and processing techniques. State
- of - the art parallel computer systems can be characterized into three structural
classes: pipelined computers, array processors and multi-processor systems. Parallel
processing computers provide a cost-effective means to achieve high system performance
through concurrent activities.
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