Unix is a Multi-user and Multi-tasking operating system
MULTICS (MULTIplexed Information and Computing Service) (1965)
Ken Thompson (Bell Laboratories -1969)
Space Wars, PDP-7, written in ASSEMBLER
UNICS (UNiplexed Information and Computing Service)
Ken Thompson, Dennis Ritchie (1970-1974)
Ritchie develops C language (starting from B language)
The third version of UNIX is written in C
A paper on UNIX is published in 1974 (ACM Turing Award 1984)
The Unix System
History, Bell Labs and AT&T UNIX
PDP-11 is the computer of many departments of computer science and so UNIX becomes the OS of the Universities
Bell Labs and AT&T UNIX development groups develop several version of UNIX:
first edition (1969), …,seventh edition (1978,on PDP-11/70)
a version for Interdata 8/2 and VAX
UNIX for a network of computers
System III (1982 - first commercial version)
System V based on System III(1983)
System V release 2, 3, 4 (1984 - 1989)
SVR4 (System V release 4; 1989 AT&T and Sun Micro systems)
1993: AT&T becomes a phone company and sells UNIX to Novell
The Unix System
History University of California at Berkeley
The most influential of the non-Bell Labs and non-AT&T UNIX development groups:.
Thompson and some students develop 1BSD (Berkeley Software Distributions) starting from sixth edition (the first one out of Bell Labs) (1978).
3BSD - 4BSD UNIX resulted from DARPA funding to develop a standard UNIX system for government use.
This series contains 4.1BSD, 4.2BSD, 4.3BSD and 4.4BSD (1980-93) and has some important new tools: virtual memory , paging, multiuser, network connection by means of TCP/IP .
4.2BSD contains the text editor vi , the shell csh , Pascal and Lisp compilers, …
Sun Microsystem, DEC and some other companies decides to develop their UNIX version starting from BSD versions instead of System V.
History of UNIX Versions
The Standardization Projects
Several standardization projects seek to consolidate the variant flavors of UNIX leading to one programming interface to UNIX. The most important are:
POSIX (Portable Operating System): merge of System V and BSD (1984)
IBM, DEC, Hewlett-Packard create OSF (Open Software Foundation) and their UNIX system is OSF/1 (1988)
X/OPEN defines the Single UNIX specification (1993) and the systems satisfying this specification have the trademark UNIX 95
Open group (merge of Open Software Foundation and X/OPEN; http://www.opengroup.com 1996)
Definition of the second version of the Single UNIX specification (1997) with the trademark UNIX 98
A variant of the UNIX System
Although there are many version of UNIX, the most important companies provide version based on UNIX System V Release 4 ( SVR4 ) and the last the Single UNIX specification
ex. Solaris 2.x is the most widely used and most successful commercial UNIX implementation.
These systems are very big and very complicated (the contrary of the Thompson’s basic idea) and in same case expensive.
So, Tanenbaum develops MINIX (1987) a small free UNIX system (11800 rows of C code and 800 rows of Assembler code) satisfying POSIX.
MINIX is a free educational system based on micro-kernel model ( www.cs.vu.nl/~ast/minix.html )
Common System Components of an OS
Main Memory Management
Secondary Memory Management
I/O System Management
Command-Interpreter System (Shell)
System structure: defines the connections and manages the System Components
Some system structures
Client-Server model (micro-kernel)
Monolithic Operating System Structure
A monolithic system has not a well defined structure. It includes virtually all of the operating-system functionality in one large block of code that runs as a single process with a single address space. All the functional components of the kernel have access to all of its internal data structures and routines.
The Client-Server Model
Moves as much from the kernel into “ user ” space. In this way it remains only a micro-kernel .
Communication takes place between user modules using message passing.
The Client-Server Model
easier to extend a micro-kernel
easier to port the operating system to new architectures
more reliable (less code is running in kernel mode)
Deterioration of the performances
MINIX has the I/O drivers into the kernel (this is for technical reasons connected to 8088 architecture), while the Main Memory Management, and the File Management are two different user processes.
The Linux System
There is not a free BSD system at the end of the eighties, and so many members of MINIX newsgroup ask to Tanenbaum to introduce many modifications for improving the performances of MINIX. Some of these modifications could change the original educational project of Tanenbaum, and so often he said “ NO ” to these requests.
So, Linus Torvalds using a pc 386 with MINIX develops a small but self-contained kernel in 1991 ( Linux 0.01 ), with the major design goal of UNIX compatibility (i.e., satisfying POSIX).
The first version of Linux (Linux 0.01) has some of features of MINIX (ex. File system), but the main differences between Linux and MINIX are:
The Linux kernel uses a monolithic model, and it has many more functions than the micro-kernel of MINIX.
From a theoretical point of view MINIX is better than Linux, but from a practical point of view the performances of Linux are better than that one of MINIX.
However, for a description of the point of view of Torvalds on the advantages-disadvantages of Linux-MINIX see the “ flame war ” between Torvalds and Tanenbaum in:
Rivoluzionario per caso: come ho creato Linux (solo per divertirmi) , Linus Torvalds, Garzanti
The Linux Kernel
Linux 0.01 (May 1991) had no networking, ran only on 80386-compatible Intel processors and on PC hardware, had extremely limited device-drive support, and supported only the Minix file system.
Linux 1.0 (March 1994) included these new features:
Support for UNIX’s standard TCP/IP networking protocols
BSD-compatible socket interface for networking programming
Device-driver support for running IP over an Ethernet
Enhanced file system
Support for a range of SCSI controllers for high-performance disk access
Extra hardware support
This version is sufficient compatible with UNIX and many people are interested in developing Linux under Torvald supervision.
Linux 1.2 (March 1995) was the final PC-only Linux kernel.
Released in June 1996, 2.0 added two major new capabilities:
Support for multiple architectures
Support for multiprocessor architectures
Other new features included:
Improved memory-management code
Improved TCP/IP performance
Support for internal kernel threads, for handling dependencies between loadable modules, and for automatic loading of modules on demand.
Standardized configuration interface
Available for Motorola 68000-series processors, Sun Sparc systems, and for PC and PowerMac systems.
Linux 2.2 January 1999 improves some aspects of Linux 2.0
The last release is Linux 2.4 (production) Linux 2.6.13 (development)
The Moral of the Story
Linux is a modern, free operating system based on UNIX standards.
First developed as a small but self-contained kernel in 1991 by Linus Torvalds, with the major design goal of UNIX compatibility.
Its history has been one of collaboration by many users from all around the world, corresponding almost exclusively over the Internet ( software open source ).
It has been designed to run efficiently and reliably on common PC hardware, but also runs on a variety of other platforms.
The core Linux operating system kernel is entirely original , but it can run much existing free UNIX software, resulting in an entire UNIX-compatible operating system free from proprietary code.
The Linux System
Linux uses many tools developed as part of Berkeley’s BSD operating system, System V, MIT’s X Window System, and the Free Software Foundation's GNU project .
The main system libraries were started by the GNU (GNU’s Not Unix) project (ex. gcc (GNU C compiler) ), with improvements provided by the Linux community.
Linux networking-administration tools were derived from 4.3 BSD code; recent BSD derivatives such as FreeBSD have borrowed code from Linux in return.
The Linux system is maintained by a network of developers collaborating on Internet (see /usr/src/linux/CREDITS), with a small number of public ftp sites acting as de facto standard repositories.
Standard, precompiled sets of packages, or distributions , include the basic Linux system, system installation and management utilities, and ready-to-install packages of common UNIX tools.
The first distributions managed these packages by simply providing a means of unpacking all the files into the appropriate places; modern distributions include advanced package management.
Red Hat, Debian, SuSE, Mandrake are popular distributions from commercial and noncommercial sources, respectively (see www.linux.org ).
The RPM Package file format permits compatibility among the various Linux distributions (see www. linuxbase .org ).
Which distribution to use ?
RedHat ( www.redhat.com )
Big, professional, very widely used
Debian ( www.debian.org/ )
Open development model, excellent packaging system
Mandrake ( www. mandrakesoft .com )
Aims to be very easy to install and use
SuSE ( www.suse.com/ )
Compromise between Red Hat and Mandrake
Slackware ( www.slackware.com/ )
Most traditional; little extra help
Linux is an intrinsically multi-user system
Every user on the system has its own username and password
The root user has ultimate power to run the system. You should not log in as root unless you really need to.
During installation, you should have been prompted for a root password and also a username and password for an ordinary user account .
The command passwd allows to change the password.
Careful : you have to perform the program shutdown –h now before to switch off the PC
The Linux kernel is distributed under the GNU General Public License (GPL) , the terms of which are set out by the Free Software Foundation .
The main consequence of GPL is that anyone using Linux, or creating their own derivative of Linux, may not make the derived product proprietary; software released under the GPL may not be redistributed as a binary-only product.
For a deeper examination of this subject see www.gnu.org/home.it.html