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Modern Operating Systems by Herbert Bos and Andrew...
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Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 1052
SEC. 12.5
In practice, large companies, which have had long experience producing soft-
ware and know what happens if it is produced haphazardly, have a tendency to at
least try to do it right.
In contrast, smaller, newer companies, which are in a huge
rush to get to market, do not always take the care to produce their software careful-
ly. This haste often leads to far from optimal results.
Neither Brooks nor Mills foresaw the growth of the open source movement.
While many expressed doubt (especially those leading large closed-source soft-
ware companies), open source software has been a tremendous success. From large
servers to embedded devices, and from industrial control systems to handheld
smartphones, open source software is everywhere. Large companies like Google
and IBM are throwing their weight behind Linux now and contribute heavily in
code. What is noticeable is that the open source software projects that have been
most successful have clearly used the chief-programmer model of having one mind
control the architectural design (e.g., Linus Torvalds for the Linux kernel and
Richard Stallman for the GNU C compiler).
12.5.3 The Role of Experience
Having experienced designers is absolutely critical to any software project.
Brooks points out that most of the errors are not in the code, but in the design. The
programmers correctly did what they were told to do.
What they were told to do
was wrong. No amount of test software will catch bad specifications.
Brooks’ solution is to abandon the classical development model illustrated in
Fig. 12-11(a) and use the model of Fig. 12-11(b). Here the idea is to first write a
main program that merely calls the top-level procedures, initially dummies. Start-
ing on day 1 of the project, the system will compile and run, although it does noth-
ing. As time goes on, real modules replace the dummies.
The result is that system
integration testing is performed continuously, so errors in the design show up much
earlier, so the learning process caused by bad design starts earlier.
A little knowledge is a dangerous thing. Brooks observed what he called the
second system effect
Often the first product produced by a design team is mini-
mal because the designers are afraid it may not work at all.
As a result, they are
hesitant to put in many features. If the project succeeds, they build a follow-up
system. Impressed by their own success, the second time the designers include all
the bells and whistles that were intentionally left out the first time.
As a result, the
second system is bloated and performs poorly.
The third time around they are
sobered by the failure of the second system and are cautious again.
The CTSS-MULTICS pair is a clear case in point.
CTSS was the first general-
purpose timesharing system and was a huge success despite having minimal func-
tionality. Its successor, MULTICS, was too ambitious and suffered badly for it.
The ideas were good, but there were too many new things, so the system performed
poorly for years and was never a commercial success. The third system in this line
of development, UNIX, was much more cautious and much more successful.

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