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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
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 43
12
INTRODUCTION
CHAP. 1
Job 3
Job 2
Job 1
Operating
system
Memory
partitions
Figure 1-5.
A multiprogramming system with three jobs in memory.
Another major feature present in third-generation operating systems was the
ability to read jobs from cards onto the disk as soon as they were brought to the
computer room. Then, whenever a running job finished, the operating system could
load a new job from the disk into the now-empty partition and run it. This techni-
que is called
spooling
(from
Simultaneous Peripheral Operation On Line
) and
was also used for output. With spooling, the 1401s were no longer needed, and
much carrying of tapes disappeared.
Although third-generation operating systems were well suited for big scientific
calculations and massive commercial data-processing runs, they were still basically
batch systems. Many programmers pined for the first-generation days when they
had the machine all to themselves for a few hours, so they could debug their pro-
grams quickly. With third-generation systems, the time between submitting a job
and getting back the output was often several hours, so a single misplaced comma
could cause a compilation to fail, and the programmer to waste half a day. Pro-
grammers did not like that very much.
This desire for quick response time paved the way for
timesharing
, a variant
of multiprogramming, in which each user has an online terminal.
In a timesharing
system, if 20 users are logged in and 17 of them are thinking or talking or drinking
coffee, the CPU can be allocated in turn to the three jobs that want service. Since
people debugging programs usually issue short commands (e.g., compile a five-
page procedure†) rather than long ones (e.g., sort a million-record file), the com-
puter can provide fast, interactive service to a number of users and perhaps also
work on big batch jobs in the background when the CPU is otherwise idle. The
first general-purpose timesharing system,
CTSS
(
Compatible Time Sharing Sys-
tem
), was developed at M.I.T. on a specially modified 7094 (Corbato
´ et al., 1962).
However, timesharing did not really become popular until the necessary protection
hardware became widespread during the third generation.
After the success of the CTSS system, M.I.T., Bell Labs, and General Electric
(at that time a major computer manufacturer) decided to embark on the develop-
ment of a ‘‘computer utility,’’that is, a machine that would support some hundreds
†We will use the terms ‘‘procedure,’’ ‘‘subroutine,’’ and ‘‘function’’ interchangeably in this book.
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