Author: Ed H. Chi (ehhchi@epx.cis.umn.edu)
Unix is an operating system designed at the Bell Laboratories of AT&T back in the 1970s. It started out in 1969 when the famous Dennis Ritchie and Ken Thompson decided to put the little-used old PDP-7 machine in the corner of the lab back to life. The name "UNIX", or at first "Unics," was intended as a pun on "Multics," which was an operating system developed at MIT. For the first 10 years, Unix development was essentially confined to Bell Labs at AT&T. The initial versions were for DEC's PDP-11 16-bit machine, and later it moved on to a VAX computers.
Unix was a landmark in operating system design and implementation. The C language was originally designed for the Unix operating system, and hence there is a strong synergy between C and Unix. After Unix was rewritten in C in 1973 (the year I was born), it could now be ported to a new hardware in months, and changes became easier. Many companies took the source code and modified it to create this own version of Unix. The development progressed at AT&T for many years, and now its version of Unix is called "System V." The Computer System Research Group of the University of California at Brekeley has their own flavor of Unix called the BSD, or the Brekeley System Distribution.
System V and BSD are the two main flavors of Unix. UNIX now comes in an incredible variety of flavors that are being shipped by various computer vendors. Unfortunately, most Unices (the plural form of Unix) are derived more or less directly from AT&T code (some code from the first C version is presumably still left in most Unices). Due to the incompatibility problems between Unices, the IEEE has begun to standardize Unix by specifying the usual features of Unix in the POSIX specification.
Since most Unices are derived from AT&T's proprietary code, a royalty fee must be paid for each copy of the operating system sold. Luckily, there are also Unix clones (i.e. Unix-compatible systems with no AT&T code).
Because Linux is free and runs on one of the most popular platforms, the IBM PC compatibles, it had became one of the best known Unices available for the Intel 386/486 machines. Many popular Unix magazines have mentioned Linux, including UnixWorld, Unix Review, and even Computer Shopper.
The most amazing of it all is that Linux was started and mostly developed by a 22-year-old computer science student, Linus Torvalds, at University of Helsinki in Finland.
When he had scrounged up enough money, he bought an 386 compatible machine to run Minix. However, Minix was not even available in Finland. So he played the popular game called "Prince of Persia" while he waited for the Minix disks to arrive in the mail. Getting Minix was not altogether a pleasant experience for him, because it did not exactly act like the Suns. It lacked various features, such as job control and fpu support. It's memory management was also lacking.
At first, Linus experimented with the protected mode of the 386 CPU in April of 1991. He wrote a protected mode program that printed "Hello world" to the screen. Then he created two seperate processes. One printed "aaaa", while the other printed "bbbb." Then, a terminal emulator was written in protected mode. Slowly, the pieces started to come together. The device driver for the hard disk was written. By October 5th, gcc (a C compiler) was running on version 0.02. When Linux Version 0.11 came out, the development was plain sailing from this point on. Just before Christmas 1991, the swapping code for a virtual memory system was in place.
The next version (0.12) came out one year after Linus bought the computer, and it was the version that finally got popular. By that time it was a very much a valid alternative to Minix. In fact, the name "Linux" stands for "Linus' Minix!"
Most of the common Unix tools and programs have been ported to Linux. Actually, ported is often too strong a word, since many programs compile out of the box without modifications, or only small modifications, because Linux tracks POSIX quite closely. The programs include all of the basic unix commands, GNU C and C++ compilers and GDB debugger, GNU emacs, most unix command shells, news and mail programs, TeX typesetting processing system, X window environment, and games. All of these programs are freely available. There is even a MS-DOS emulator currently in testing that will allow you to run DOS programs.
An Intel 486DX 33MHz machine will run faster than a Sun SparcStation 2, and a 486DX/2 66 MHz machine will run almost four times faster than the same SparcStation 2 according to the BYTE Unix benchmark. The same 486DX/2 66 MHz machine is only about a quarter times slower than the Sun Sparc 10 according to the Dhrystone 2.1 benchmarks. In fact, what is even more mind boggling is that an Intel Pentium machine will surely surpass the Sparc 10's. An Intel Pentium machine can be obtained for just under three thousand dollars now. What a enormous amount of computing power on a inexpensive Unix machine!
For those of you computer junkies out there, here is a list of Linux' features:
* multiprograming: several programs running at once.
* multiuser: several users on the same machine at once.
* has memory protection between processes, so that one program can't bring the whole system down.
* demand loads executables: Linux only reads from disk those parts of a program that are actually used.
* shared copy-on-write pages among executables. This means that multiple process can use the same memory to run in. When one tries to write to that memory, that page (4KB piece of memory) is copied somewhere else. Copy-on-write has two benefits: increasing speed and decreasing memory use.
* virtual memory using paging
* a unified memory pool for user programs and disk cache (so that all free memory can be used for caching, and the cache can be reduced when running large programs).
* dynamically linked shared libraries (DLL's)
* does core dumps for post-mortem analysis.
* POSIX job control.
* pseudoterminals (pty's).
* 80387 math coprocessor emulation in the kernel so that programs don't need to do their own math emulation.
* support for many national or customized keyboards
* multiple virtual consoles: several independent login sessions through the console
* Supports several common filesystems, including Minix-1 and Xenix, and has an advanced filesystem of its own, which offers filesystems of up to 4 terabytes, and file names up to 255 characters long.
* transparent access to MS-DOS filesystems and OS/2 partitions. You don't need any special commands to use the MS-DOS filesystem, it looks just like a Unix filesystem.
* CD-ROM support: can read all standard formats of CD-ROM filesystems
* TCP/IP networking over Ethernet and SLIP, including ftp, telnet, NFS, etc.
-- comp.os.linux.announce is a moderated newsgroup for announcements about Linux (new programs, bug fixes, etc).
-- comp.os.linux.admin is an unmoderated newsgroup for discussion of administration of Linux systems.
-- comp.os.linux.development is an unmoderated newsgroup specifically for discussion of Linux kernel development. The only application development questions that should be discussed here are those that are intimately associated with the kernel.
-- comp.os.linux.help is an unmoderated newsgroup for any general questions a Linux user might have.
-- comp.os.linux.misc is meant for any discussion that doesn't belong elsewhere.
Linux is being developed using an open and distributed model, instead of a closed and centralized model like much other software. This means that the current development version is always public (with up to a week or two's delay) so that anybody can use it. The result is that whenever a version with new functionality is released, it almost always contains bugs. However, it also results in a very rapid development, because the bugs are generally discovered within hours of a kernel release, and corrected quickly, especially those which might endanger a user's data, so it is easy for an end-user to avoid these bugs.
Evidences show that the Linux user base is quite large. Several businesses exist now that solely depend on selling and supporting Linux, such as SoftLanding Software, InfoMagic, Trans-Ameritech, and Clark Internet Services. Moreover, the Linux newsgroups are some of the most heavily read and posted on the Internet.
However, one brave soul, Harald T. Alvestrand, has decided to try to get an idea of what the Internet Linux user base looks like. According to his registration program, as of Janurary 4th, 1994, there are 4495 Internet users in his counting program. 74 percent of these users uses Linux at home, and 25 percent of these users actually uses Linux at work! There are Linux users in countries such as Iceland, Norway, Denmark, Slovenia, Estonia, Hong Kong, Taiwan, Isreal, Brazil, and South Africa. Since many of the users actually get their copy of Linux through BBS'es (Bulletin Board Systems), the number of Linux users could be well over 40,000 users(4) and the number is growing fast.
Interestingly enough, Linux is already being used in critical missions. The Australian Surveying and Land Information Group in Canberra have decided to go with Linux based systems. These systems are being installed in Antarctica! Andrew Tridgell, the designer of these Linux systems, told about his project recently in comp.os.linux.misc:
You can ask friends and user groups for a copy of Linux, or order one of the commmercial distributions. For the Internet users, there are several distributions that are available at SunSite.unc.edu:/pub/Linux/distributions/.
There is a 150 page guide on getting, installing, and setting up Linux, which is available at tsx-11.mit.edu:/pub/linux/docs/LDP/install-guide-1.ps.gz. In addition, the Linux Documentation Project has put out several other books in various states of completion, and these are available at sunsite.unc.edu:/pub/Linux/docs/LDP/. Over 600 pages of documentation in book form have been released by the LDP alone, plus a large group of manual pages.
Documentation is not yet completed, but is being actively worked on by those on the ``Linux Documentation Project.'' There is a MS-Windows binary emulator called WINE being developed by a group of people. Once it is completed, the user will be able to run MS-Window programs directly under Linux and X Windows.
Work is underway on Linux version 1.0, which will close some of the gaps in the present implementation. The consensus is that once the networking code has been stablized, version 1.0 will be released.
All of this development work was done in two years! So watch out Microsoft! Linux could become the perfered operating system on the PC platform, and challange the wave of the future!