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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 752
SEC. 10.1
HISTORY OF UNIX AND LINUX
721
Linux rapidly grew in size and evolved into a full, production UNIX clone, as
virtual memory, a more sophisticated file system, and many other features were
added. Although it originally ran only on the 386 (and even had embedded 386 as-
sembly code in the middle of C procedures), it was quickly ported to other plat-
forms and now runs on a wide variety of machines, just as UNIX does. One dif-
ference with UNIX does stand out, however: Linux makes use of so many special
features of the
gcc
compiler and would need a lot of work before it would compile
with an ANSI standard C compiler.
The shortsighted idea that
gcc
is the only com-
piler the world will ever see is already becoming a problem because the open-
source LLVM compiler from the University of Illinois is rapidly gaining many
adherents due to its flexibility and code quality.
Since LLVM does not support all
the nonstandard
gcc
extensions to C, it cannot compile the Linux kernel without a
lot of patches to the kernel to replace non-ANSI code.
The next major release of Linux was version 1.0, issued in 1994.
It was about
165,000 lines of code and included a new file system, memory-mapped files, and
BSD-compatible networking with sockets and TCP/IP.
It also included many new
device drivers. Several minor revisions followed in the next two years.
By this time, Linux was sufficiently compatible with UNIX that a vast amount
of UNIX software was ported to Linux, making it far more useful than it would
have otherwise been.
In addition, a large number of people were attracted to Linux
and began working on the code and extending it in many ways under Torvalds’
general supervision.
The next major release, 2.0, was made in 1996.
It consisted of about 470,000
lines of C and 8000 lines of assembly code.
It included support for 64-bit architec-
tures, symmetric multiprogramming, new networking protocols, and numerous
other features.
A large fraction of the total code mass was taken up by an extensive
collection of device drivers for an ever-growing set of supported peripherals. Addi-
tional releases followed frequently.
The version numbers of the Linux kernel consist of four numbers,
A.B.C.D
,
such as 2.6.9.11. The first number denotes the kernel version. The second number
denotes the major revision. Prior to the 2.6 kernel, even revision numbers corre-
sponded to stable kernel releases, whereas odd ones corresponded to unstable revi-
sions, under development. With the 2.6 kernel that is no longer the case. The third
number corresponds to minor revisions, such as support for new drivers. The fourth
number corresponds to minor bug fixes or security patches.
In July 2011 Linus
Torvalds announced the release of Linux 3.0, not in response to major technical ad-
vances, but rather in honor of the 20th anniversary of the kernel. As of 2013, the
Linux kernel consists of close to 16 million lines of code.
A large array of standard UNIX software has been ported to Linux, including
the popular X Window System and a great deal of networking software. Two dif-
ferent GUIs (GNOME and KDE), which compete with each other, have also been
written for Linux.
In short, it has grown to a full-blown UNIX clone with all the
bells and whistles a UNIX lover might conceivably want.
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