|
Items in cart [0] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 307
307
data bases should be continued and expanded (see Section
VII, Astronomical Data Bases).
III. THE TREND TOWARD DECENTRALIZATION
When computers first appeared on the scene, they were
large, costly, temperamental machines. This led to the
establishment of centralized computer centers that pur-
chased (or leased) the computer and associated peripherals
and provided computer services to a community of users
each of whom could not afford individually to purchase
the computer. Because computer centers were the only
computer facilities available, the users had to tailor
the problems to be addressed and their working habits to
the capabilities and schedules of the computer centers.
As computer technology developed, the mainframes became
more reliable and more powerful but not appreciably less
costly. (To be sure, the price/performance ratio improved
dramatically, but this was accomplished by selling more
performance at the same price.) Many university computer
centers expanded their clientele so that the original
science and engineering users of the computer centers
were now competing for resources with administrators,
managers, the general student population, computer-science
students, word processors, game players, and other non-
science and nonengineering users. Because of the influx
of nontechnically oriented users, computer center staffs
were expanded in order to provide support services and to
make the computer appear easy to use. None of these
developments was necessarily bad, but in many cases they
had the consequence that the improved price/performance
ratios of newer computers were exploited to provide
additional system services rather than additional come
putational power. That is, many computer centers are
charging the same amount per computation in real dollars
today that they charged ten years ago.
In addition, university computer centers have been
reluctant to support the video image display and hardcopy
capability required for astronomical image processing
(and, to a lesser extent, for astronomical theory).
While the preceding presents a rather dismal picture
of the traditional computer center, it must be emphasized
that not all computer centers suffer from these problems;
there are some astronomers who are pleased with the per-
formance of their university centers. Computer centers
with specific missions such as those at the Lawrence
OCR for page 308
308
Livermore Laboratory or the National Center for Atmo-
spheric Research have generally been successful in
providing high-quality services at reasonable cost.
In the 1960's, the first minicomputer appeared. Mini-
computers took advantage of the same technology used in
the mainframes but used this technology to decrease costs
rather than increase performance. Since their introduc-
tion, the performance of minicomputers has steadily
increased so that today the main difference (from the
viewpoint of a scientific user) between a top-of-the-line
minicomputer and a typical mainframe is mostly cost. (To
be sure, the mainframe is supplied with several simul-
taneously running operating systems, support for many
high-level languages, accounting software, word-processing
software, and so on, but these capabilities are seldom
used in scientific applications.)
An example should make this clear. The most powerful
commercially available scientific computer is a vector
machine that accommodates up to 65 Mbytes of main memory,
costs about $10 million (with some peripherals), and has
a computational capability equal to about 100 MFLOPS
(million floating point operations per second). Mini-
computers (sometimes called supermini's) are now available
with 32-bit virtual memories, 8 Mbytes of main memory
(which will increase to 32 Mbytes when 64-kbit memory
chips become widely available), and a performance of 1-2
MFLOPS. Such a machine costs about $220,000 (with some
peripherals).
Benchmarks indicate that a large vector machine is
about 75 times as powerful as a typical supermini and
therefore is about two times as cost-effective. However,
an array processor can be attached to a supermini for
about $80,000 and improves its performance by about a
factor of 10. Thus a supermini with array processor can
be about four times as effective and one eighth as fast
as a powerful vector machine. A note of caution, how-
ever--benchmark tests are highly application dependent.
Furthermore, peripherals can be a large component of the
cost of a system. Therefore, the price-performance data
given above must be treated as coarse averages and may be
expected to vary from application to application.
Of course, university computer centers do not have the
top-of-the-line vector machines, and minicomputers all by
themselves (without array processors) provide more cost-
effective computing than is available from typical
university computer centers.
Representative terms from entire chapter:
university computer
