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Hardware (Physical) Layer of an Operating System

    The Hardware Level of the operating system controls the use of physical system resources, such as the memory manager, process manager, disk drivers, etc.


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    This layer of an operating system is often called the kernel. The exact boundaries of what constitutes the kernel varies by OS and often includes portions of the Logical Layer.

kernels in use

     BSD: FreeBSDe104, ULTRIXe100

     MACH: Digital UNIXe45, Mac OS Xe75, Mac OS X Servere75, MkLinux (PowerPC, Intel, and HP/PA)e75, NeXT (2.5)e44, Rhapsodye75

     LINUX: LINUXe61

     Proprietary: (NOTE: Each would be a different proprietary kernel) AmigaOS, BeOS, IRIXe46, Macintosh, MVS, NetWare, OpenVMS, OS/2, Pyramide97, Windows

kernels by operating system

    Digital UNIX: Mach 2.5-based implementation of BSD 4.xe45

     FreeBSD: BSD 4.4 + enhancementse104

     IRIX: Proprietary. “SGI has put a lot of work into IRIX; it isn’t just someone else’s kernel with some bundled software on top. It also predates MACH or any other open unix standard by a number of years.” — Walter Robersone46

     LINUX: LINUX. “The Linux kernel was originally written by Linus Torvalds (hence the name “Linux”), and it maintained by a team of developers. The kernel itself is released under the GPL (GNU Public License).” —Rich Steinere61 (See also: http://www.linuxhq.org

     Mac OS X: Mache75

    Mac OS X Server: Mache75

     NeXT: Mach 2.5-based implementation of BSD 4.xe44

    Netware: Proprietary.e97

     Rhapsody: Mach 2.5 (with custom enhancements)e75

number of bits

    One area of operating system support is how many bits of address and data space it can deal with. Early microprocessors were typically four or eight bits, while early mainframes and minicomputers were typically eight or twelve bits. Modern mainframes and microcomputers are typically either 32 or 64 bits.

    The biggest advantage of more bits is a larger addressable space, both more RAM and larger disk (or other) storage space.

    The bit-ness of an operating system or even of application programs can greatly exceed that of the underlying hardware. Classic examples include multi-precision mathematics in science and engineering and large data space in graphics software.

    The bit-ness of the hardware can exceed that of the operating system or application programs. This is generally not a problem. It can lead to inefficiencies in operand fetches or writes and in allocation of data storage space, although this is not normally the case as hardware generally keeps smaller bitsize operations in the instruction set.

    A related situation is the running of old legacy software on modern hardware. This can lead to inefficiencies in both allocation of space and in fetch and write of operands. The typical solution is for an operating system to provide an environment for legacy software that recreates the expectations of the older software.

    In general, the more bits an operating system can handle, the more ready it is for the upcoming demands of truely large graphics and database operations, as well as being able to smoothly scale many everyday processes to the size needed for a large scale operation (such as web servers handling huge amounts of traffic). Most modern operating systems are in the process of the changeover to 64-bit hardware.

     Digital UNIX continues to dominate the 64-bit arena, leaving HP-UX and IRIX to contest the second position, followed closely by AIX. Solaris and NT trail significantly behind. Digital benefits not only from strong software support for 64-bits, now being matched by other players, but also from top-to-bottom 64-bit hardware support and a lack of the minor compatibility tradeoffs required by other vendors’ solutions. AIX offers good backwards compatibility for 32-bit applications and a few other compatibility bonuses. However, IBM has lagged behind its competitors in providing 64-bit hardware, shipping its first 64-bit server only now. HP scores slightly better, having progressed about halfway through its hardware transition to 64-bits, also offering good backwards compatibility for 32-bit applications. IRIX has transitioned its hardware line completely to 64-bit technology, but lags in the area of 64-bit standards conformance, without support for the predecessor of the 64-bit UNIX98 standard, UNIX95. Solaris is the sole UNIX operating system that does not yet provide support for 64-bit processes, so it falls somewhat further behind and potential compatibility issues remain largely unknown. Still, Sun has migrated over half its product line to 64-bit hardware, and provides support for large amounts of physical memory, both of which are still missing from NT. NT runs on 64-bit Alpha hardware and offers 64-bit files and file systems but has yet to address the key 64-bit requirement to support large amounts of physical memory for enhancing database performance.” —D.H. Brown Associatesw43

    64-bit OSs: BeOS, Digital UNIX, HP-UX, IRIX, LINUX (depending on the processor used)w90, Mac OS X, Mac OS X Server, NetBSDe113, OpenVMS (on Alpha) e111, Solarise107, Sun-OSe107

    32-bit OSs: Amigae95, FreeBSD, LINUX (depending on the processor used)w90, Macintosh, NeXT, OpenVMS (on VAX) e111, OS/2, Pyramide97, Rhapsody, Solaris, ULTRIX, Windows 95, Windows 98, Windows NT, Windows NT Server, Windows NT Server Enterprise Edition

    24-bit OSs: Windows 3.1

    16-bit OSs: MS-DOS


    Some operating systems can support more than one processor in a single machine. This is called multiprocessing.

    “Writing an efficient, scalable mp kernel is not an easy task.” —Orphye74

number of processors supported:

     IRIX: 128 processorsw34

     HP-UX: 128 processorse121

     Solaris: 64 processorse64

     SUN-OS: 64 processorse64

     OS/2: 64 processorse122

     OpenVMS: 32 processorse120

     Mac OS X: 32 processorse125

     Rhapsody: 32 processorse125

     AIX: 24 processors (in the S80 model )e112

    Pyramid: 24 processorse65

     BeOS: 8 processorse82

     Windows 2000 Advanced Server: 8 processorsw50

    ULTRIX: 6 processors (in some models of VAX 6000)e100

     FreeBSD : 4 processors (Intel SMP)e104

     Macintosh : 4 processorse114

     Windows 2000 Server: 4 processorsw50

     Windows NT: 4 processors —Jim Carr, MicroTimes; Oct 30, 1998m1

     Windows 2000 Professional: 2 processorsw50

     Amiga: 2 (one 68060 and one PowerPC)e95

     NetBSD: 1e113

     NeXT: 1e132 “Max. Processors was 1 on all architectures. Rhapsody and OPENSTEP will work on some multiple CPU Intel systems, but will only use the first CPU.“—Graham J Leee132

    MS-DOS: 1

    It’s going to take me a while to get all of the operating systems charted and footnoted. Please be patient. Thanks.


     OS/2 Warp: “real multitasking for greater productivity”w27

related web sites

    http://www.dhbrown.com/cfeprise/page_int.cfm?OBJECTID=131&Method=VIEW “Operating System Scorecard — 64 bits — D.H. Brown Associates”

geek humor

    “That kernel’s got a mean streak a MILE WIDE!!” —Chip Salzenberg

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    Copyright © 1998, 1999, 2000, 2001, 2004, 2006 Milo

    Last Updated: September 11, 2006

    Created: June 4, 1998

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