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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 80
SEC. 1.5
OPERATING SYSTEM CONCEPTS
49
hardware was added and multiprogramming became possible. Until this day, many
embedded systems have no protection hardware and run just a single program.
Now let us look at operating systems. The first mainframes initially had no
protection hardware and no support for multiprogramming, so they ran simple op-
erating systems that handled one manually loaded program at a time. Later they ac-
quired the hardware and operating system support to handle multiple programs at
once, and then full timesharing capabilities.
When minicomputers first appeared, they also had no protection hardware and
ran one manually loaded program at a time, even though multiprogramming was
well established in the mainframe world by then. Gradually, they acquired protec-
tion hardware and the ability to run two or more programs at once. The first
microcomputers were also capable of running only one program at a time, but later
acquired the ability to multiprogram. Handheld computers and smart cards went
the same route.
In all cases, the software development was dictated by technology. The first
microcomputers, for example, had something like 4 KB of memory and no protec-
tion hardware. High-level languages and multiprogramming were simply too much
for such a tiny system to handle.
As the microcomputers evolved into modern per-
sonal computers, they acquired the necessary hardware and then the necessary soft-
ware to handle more advanced features.
It is likely that this development will con-
tinue for years to come.
Other fields may also have this wheel of reincarnation, but
in the computer industry it seems to spin faster.
Disks
Early mainframes were largely magnetic-tape based. They would read in a pro-
gram from tape, compile it, run it, and write the results back to another tape. There
were no disks and no concept of a file system.
That began to change when IBM
introduced the first hard disk—the RAMAC (RAndoM ACcess) in 1956.
It occu-
pied about 4 square meters of floor space and could store 5 million 7-bit charac-
ters, enough for one medium-resolution digital photo. But with an annual rental fee
of $35,000, assembling enough of them to store the equivalent of a roll of film got
pricey quite fast. But eventually prices came down and primitive file systems were
developed.
Typical of these new developments was the CDC 6600, introduced in 1964 and
for years by far the fastest computer in the world. Users could create so-called
‘‘permanent files’’ by giving them names and hoping that no other user had also
decided that, say, ‘‘data’’ was a suitable name for a file. This was a single-level di-
rectory.
Eventually, mainframes developed complex hierarchical file systems, per-
haps culminating in the MULTICS file system.
As minicomputers came into use, they eventually also had hard disks. The
standard disk on the PDP-11 when it was introduced in 1970 was the RK05 disk,
with a capacity of 2.5 MB, about half of the IBM RAMAC, but it was only about
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