The Linux FAQ page 3 The Linux Kernel

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This is the list of Frequently Asked Questions for Linux, the Free/Open Source UNIX-like operating system kernel that runs on many modern computer systems..

Table of Contents

. The Linux Kernel

Q: What Platforms Does Linux Support?

Q: What Hardware Is Supported?

Q: Ports to Other Processors

Q: How Does Linux Kernel Versioning Work?

Q: Where Is the Latest Kernel Version on the Internet?

Q: Does Linux Support Threads or Lightweight Processes?

Q: What Version of Linux and What Machine Name Is This?

Q: What is a BogoMip?

Q: Does Linux Support USB Devices?

Q: Can Linux Use More than 3 Serial Ports by Sharing Interrupts?

Q: What Platforms Does Linux Support?

A: Linux runs on almost every general-purpose computer made in the last 10 years. It runs on systems assmall as PDAs (for example, the Sharp Zaurus) and on systems as large as IBM mainframes.There are Linux distributions specifically for mobile and handheld platforms. Information on the Linux

distribution for the Compaq iPAQ is at http://www.handhelds.org.

 

A: Linux was written originally for Intel processor based PC's, using the hardware facilities of the 80386processor and its successors to implement its features. The 80386 family includes the 80486 and all of the

Pentium chips. However, there are now many ports to other hardware platforms. See Ports to Other

Processors. Refer also to the Linux INFO-SHEET for more details as well as the answers to Where Is the

Documentation?, What Hardware Is Supported?, and Ports to Other Processors, below.

Q: What Hardware Is Supported?

A: A minimal Linux installation requires a machine for which a port exists, at least 2Mb of RAM, and a

single floppy drive, but to do anything even remotely useful, more RAM and disk space are needed. Refer to:

Ports to Other Processors, What are the Disk Space Requirements for Minimal, Server, and Workstation

Use?, and What are the Minimum and Maximum Memory Requirements?.

Intel CPU, PC-compatible machines require at least an 80386 processor to run the standard Linux kernel.

Linux, including the X Window System GUI, runs on most current laptops. Refer to the answer for: How Do I

Find Out If a Notebook Runs Linux?. There are numerous sources of information about specific PC's, video

cards, disk controllers, and other hardware. Refer to the INFO-SHEET, Laptop-HOWTO, and the

Unix-Hardware-Buyer-HOWTO. See Where Is the Documentation?.

Q: Ports to Other Processors

A: Ports are currently available for:

Compaq Alpha AXP ·

Sun SPARC and UltraSPARC ·

Motorola 68000 ·

3. The Linux Kernel 6.PowerPC ·

PowerPC64 ·

ARM ·

Hitachi SuperH ·

IBM zSeries and S/390 ·

MIPS ·

HP PA-RISC ·

Intel IA-64 ·

DEC VAX ·

AMD x86-64 ·

CRIS ·

 

 

 

A: There are always efforts underway to port Linux onto new processors. On Intel platforms, VESA Local Bus and PCI bus are supported.MCA (IBM's proprietary bus) and ESDI hard drives are mostly supported. There is further information on the

Refer also to the answer for: Where Is the Linux Stuff on the World Wide Web?.

There is a port of Linux to the 8086, known as the Embeddable Linux Kernel Subset (ELKS). This is a 16-bit

subset of the Linux kernel which will mainly be used for embedded systems, Standard Linux does not run 8086 or 80286 processors, because itrequires task-switching and memory management facilities found on 80386 and later processors.Linux supports multiprocessing with Intel MP architecture. See the file Documentation/smp.tex in theLinux kernel source code distribution.An API specification and developers kit for the Crusoe Smart Microprocessor developed by Transmeta

Corporation are at http://www.transmeta.com .

A project has been underway for a while to port Linux to suitable 68000-series based systems like Amigas

and Ataris. The URL of the Linux/m68k home page is http://www.linux-m68k.org/faq/faq.html .

There is also a linux-680x0 mailing list. See What Mailing Lists Are There?.

There is (or was) a FTP site for the Linux-m68k project on ftp://ftp.phil.uni-sb.de/pub/atari/linux-68k , but

this address may no longer be current.Debian GNU/Linux has ports to Alpha, Sparc, Motorola 68k, PowerPC, ARM, IBM S/390, MIPS, HP

PA-RISC, and IA-64. A Port to amd64 is being developed. There are mailing lists for all of them. See

http://www.debian.org/MailingLists/  for general information, then follow the "subscription" link, and find the

mailing list you are interested in. One of the Linux-PPC project pages is and the archive site is ftp://ftp.linuxppc.org/linuxppc .

The Linux FAQ

3. The Linux Kernel 7.There are two sites for the Linux iMac port: http://w3.one.net/~johnb/imaclinux ,

 

Ralf Baechle is working on a port to the MIPS, initially for the R4600 on Deskstation Tyne machines. The

Linux-MIPS FTP sites are ftp://ftp.fnet.fr/linux-mips  and ftp://ftp.linux.sgi.com/pub/mips-linux . Interested

people may mail their questions and offers of assistance to linux@waldorf-gmbh.de .

There is (or was) also a MIPS channel on the Linux Activists mail server and a linux-mips mailing list. See

What Mailing Lists Are There?.There are currently two ports of Linux to the ARM family of processors. One of these is for the ARM3, fittedto the Acorn A5000, and it includes I/O drivers for the 82710/11 as appropriate. The other is to the ARM610of the Acorn RISC PC. The RISC PC port is currently in its early to middle stages, owing to the need torewrite much of the memory handling. The A5000 port is in restricted beta testing. A release is likely soon.

For more, up-to-date information, read the newsgroup news:comp.sys.acorn.misc . There is a FAQ at

http://www.arm.uk.linux.org .The Linux SPARC project is a hotbed of activity. There is a FAQ and plenty of other information available

from the UltraLinux page, http://www.ultralinux.org .

 

 

There is also a port to SGI/Indy machines ("Hardhat"). The URL is http://www.linux.sgi.com .

Q: How Does Linux Kernel Versioning Work?

A: At any given time, there are several "stable" versions of Linux, and one "development" version. Unlikemost proprietary software, older stable versions continue to be supported for as long as there is interest, whichis why multiple versions exist.Linux version numbers follow a longstanding tradition. Each version has three numbers, i.e., X.Y.Z. The "X"is only incremented when a really significant change happens, one that makes software written for one versionno longer operate correctly on the other. This happens very rarely -- in Linux's history it has happenedexactly once.The "Y" tells you which development "series" you are in. A stable kernel will always have an even number inthis position, while a development kernel will always have an odd number.The "Z" specifies which exact version of the kernel you have, and it is incremented on every release.The current stable series is 2.4.x, and the current development series is 2.5.x. However, many people continueto run 2.2.x and even 2.0.x kernels, and they als o continue to receive bugfixes. The development series is thecode that the Linu x developers are actively working on, which is always available for public viewing, testing,and even use, although production use is not recommended! This is part of the "open source development"

method.

The Linux FAQ

3. The Linux Kernel 8.Eventually, the 2.5.x development series will be "sprinkled with holy penguin pee" and become the 2.6.0kernel and a new stable series will then be established, and a 2.7.x development series begun. Or, if any really

major changes happen, it might become 3.0.0 instead, and a 3.1.x series begun.

Q: Where Is the Latest Kernel Version on the Internet?

A: The easiest way to update your kernel is to get the update directly from the distribution which you arerunning.

 

A: If you need or want to configure and compile your own kernel, the web page at http://www.kernel.org/  lists

the current versions of the development and production kernels.If you want to download the source code, FTP to ftp.xx.kernel.org,  where xx is the two-letterInternet domain abbreviation of your country; e.g., us for United States, ca for Canada, or de for Germany.Kernel versions 2.2.x are archived in the directory pub/linux/kernel/v2.2, as are patches for theprerelease versions. The kernel source code is archived as a .tar.gz file, and as a .tar.bz2 file.Follow the instructions in any of the standard references to compile the kernel, as you would with any othercustom kernel. The Documentation subdirectory contains information by the authors of varioussubsystems and drivers, and much of that information is not documented elsewhere.If you want to participate in kernel development, make sure that you sign on to the linux-kernel mailing list to

find out what people are working on. Refer to the answer: What Mailing Lists Are There?.

There is a story about the features of the 2.4 series kernels at http://features.linuxtoday.com/stories/8191.html .

Q: Does Linux Support Threads or Lightweight Processes?

A: As well as the Unix multiprocessing model involving heavyweight processes, which is of course part of thestandard Linux kernel, there are several implementations of lightweight processes or threads. Recent kernelsimplement a thread model, kthreads. In addition, there are the following packages available for Linux.GNU glibc2 for Linux has optional support for threads. The archive is available from the same place

as glibc2, ftp://ftp.gnu.org/pub/gnu/

In ftp://sipb.mit.edu/pub/pthread/  Documentation isn't in the package, but is available on the World Wide Web at http://www.mit.edu:8001/people/proven/home_page.html . Newer Linux libc's contain the pthreads

source. The GNU Ada compiler on ftp://metalab.unc.edu/pub/Linux/devel/lang/ada/  contains binaries

made from that source code.

In ftp://ftp.cs.washington.edu/pub/qt-001.tar.Z  is QuickThreads. More information can be found in

the technical report, available on the same site is /tr/1993/05/UW-CSE-93-05-06.PS.Z.·

In ftp://ftp.cs.fsu.edu/pub/PART/ , an Ada implementation. This is useful mainly because it has a lot of

Postscript papers that you'll find useful in learning more about threads. This is not directly usableunder Linux.

Please contact the authors of the packages in question for details.

Q: What Version of Linux and What Machine Name Is This?

A: Type:. The Linux Kernel 9.$ uname -a

Q: What is a BogoMip?

A: "BogoMips" is a combination of Bogus and Mips. MIPS stands for (depending on who you ask) Millions of

Instructions per Second, or Meaningless Indication of Processor Speed.

The number printed at boot time is the result of a kernel timing calibration, used for very short delay loops bysome device drivers.

According to the BogoMips mini-HOWTO, the rating for your machine will be:

Common BogoMips RatingsProcessor BogoMips Comparison--------- -------- ----------Intel 8088 clock * 0.004 0.02Intel/AMD 386SX clock * 0.14 0.8Intel/AMD 386DX clock * 0.18 1 (definition)Motorola 68030 clock * 0.25 1.4Cyrix/IBM 486 clock * 0.34 1.8Intel Pentium clock * 0.40 2.2Intel 486 clock * 0.50 2.8AMD 5x86 clock * 0.50 2.8Mips R4000/R4400 clock * 0.50 2.8Nexgen Nx586 clock * 0.75 4.2PowerPC 601 clock * 0.84 4.7Alpha 21064/21064A clock * 0.99 5.5Alpha 21066/21066A clock * 0.99 5.5Alpha 21164/21164A clock * 0.99 5.5Intel Pentium Pro clock * 0.99 5.5Cyrix 5x86/6x86 clock * 1.00 5.6Intel Pentium II/III clock * 1.00 5.6Intel Celeron clock * 1.00 5.6Mips R4600 clock * 1.00 5.6Alpha 21264 clock * 1.99 11.1AMD K5/K6/K6-2/K6-III clock * 2.00 11.1UltraSparc II clock * 2.00 11.1Pentium MMX clock * 2.00 11.1PowerPC 604/604e/750 clock * 2.00 11.1Motorola 68060 clock * 2.01 11.2Motorola 68040 Not enough data (yet).AMD Athlon Not enough data (yet).IBM S390 Not enough data (yet).If the number is wildly lower, you may have the Turbo button or CPU speed set incorrectly, or have some

kind of caching problem (as described in Why Does the System Slow to a Crawl When Adding More

Memory?).

For values people have seen with other, rarer, chips, or to calculate your own BogoMips rating, please refer to

the BogoMips Mini-HOWTO, on ftp://metalab.unc.edu/ . See Where Is the Documentation?.

[Wim van Dorst]

Q: Does Linux Support USB Devices?

The Linux FAQ 3. The Linux Kernel 10

A: Linux supports a few dozen USB devices at present, and work is underway to develop additional device

drivers. There is a Web page devoted to the subject, at http://www.linux-usb.org . There is also LDP

documentation, at: Where Is the Linux Stuff on the World Wide Web?.

Support for USB version 2.0 was recently added to development kernels, but is not yet available in the 2.4

series.

Q: Can Linux Use More than 3 Serial Ports by Sharing Interrupts?

A: Yes, but you won't be able to use simultaneously two ordinary ports which share an interrupt (withoutsome trickery). This is a limitation of the ISA Bus architecture.

See the Serial HOWTO for information about possible solutions and workarounds for this problem.

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3. The Linux Kernel 11.

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