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linux crash course chapter 01 3

Chapter 1:
Welcome to Linux
An intro to UNIX-related
operating systems

In this chapter …
• History of Unix
• GNU-Linux
• Why Linux?

Long ago, in a galaxy far away …
• Computing power was costly
– UNIVAC cost $1 million

• CPU time was a premium
– Most mainframes had less computing power than
a calculator on the shelf at Wal-Mart

• Jobs were submitted into a queue

– Only one process at a time – scheduling

What was needed
• Allow multiple users to access the same data
and resources simultaneously
• Service many users more cheaply than
buying each their own machine
• The ability to run multiple processes at once
• And do so while maintaining user
segregation and data integrity

Enter Unix, pride of Bell Labs
• Originally written in PDP-7 assembly
language by Ken Thompson
• To make it work on multiple architectures
(portable), Thompson rewrote Unix in B
• Dennis Ritchie developed C, and with
Thompson, rewrote Unix in C

What was so great about it?

Economical for business
Initially given for free to colleges and
universities (great tactic!)

Descendents and bastards …

Started at Bell Labs
Picked up and continued by AT&T (SVR4)
UC Berkeley derives BSD
Sun Solaris
Minix, XINU

What happened?
• UNIX became commercialized
• Proprietary code, specialized distributions
• Costs started to become a hindrance
• So … let’s make our own Unix …

• Richard Stallman decides that there should
be a free version of Unix available
• Forms the GNU project – GNU’s Not Unix
• Writes all of the system programs and
utilities to mimic Unix variants
• Everything but a kernel (Hurd)

Final piece
• Universities trying to teach Unix and OS
design can’t afford Unix
• Andrew Tanenbaum writes Minix
• Linus Torvalds, dissatisfied with Minix, writes
his own – Linux

• Torvalds has a perfectly functioning kernel –
but no system programs
• Finds a perfect candidate in GNU
• Together, the operating system world was
changed dramatically

Free you say?

GNU-Linux is free …
Free as in speech, not free as in beer
Free to view, copy, modify, and release
Profit still to be had from packaging, support,
and additional original code

Why Linux?



An almost limitless library of programs
Applications, services, utilities
Many free, some commercial
Source code often available along with prebuilt binaries

• Supports thousands of peripherals and
pieces of hardware
• Multi-platform: x86, PPC, Alpha, SPARC,
MIPS, 64-bit, SMP (multiproc systems)
• Emulation of hardware for testing and

• Entire operating system written in C
• Shared system libraries available for all
supported architectures
• Code written on one platform can be
compiled on any system with minimal, if any,

• Much of GNU-Linux already meets POSIX
(Portable Operating System Interface for
Computer Environments) and Unix System V
Interface Definition (SVID)
• Standardized for commercial and
government use

And don’t forget …
• It’s free! (or at least really cheap!)
• That’s why Linux is often the operating
system of choice to teach OS design and
Unix courses
• We’ll be using RedHat Enterprise Linux 4 –
not free but a fraction of the cost of Unix

Features Overview

Multiprocess / Multitasking
Hierarchical Filesystem
BASH Shell command line interface /
programming language
• Many useful utilities built-in
• Rich networking support

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