Originally published in the May 1995 issue of Advanced Systems. magazine. We update this story in the June 1996 version of SunWorld Online.


Unix OS go head-to-head

The major flavors of Unix have converged on common kernel standards, and now they look to higher layers for divergence.

By Barry D. Bowen

Long the darling of the science and engineering communities, the Unix operating systems recently have gained attention and respect in the business community. All of the major systems vendors now have "industrial-strength" versions of Unix or are developing Unix look-alikes for commercial client/server distributed-computing environments. IBM, for instance, besides offering its AIX Unix variant, recently announced that it is converting its MVS mainframe operating system into a Unix OS! That should end the debate regarding how suitable Unix is for mainstream business computing.

Nonetheless, system buyers are accustomed to choosing between only one or two versions of an OS -- Microsoft Windows on the desktop and MVS for mainframes, for example. The evolution of sometimes wildly divergent and noninteroperable Unix "flavors" from the various vendors has consequently confused the marketplace. In the minds of many, the confusion persists.

The days of confusion are over. Sometimes enthusiastically, sometimes dragged along unwillingly by market realities, particularly threats from Redmond, WA (see sidebar Windows NT looms ever stillsee sidebar), the major Unix OS vendors have increasingly coalesced around a set of more carefully defined and better understood de facto and de jure standards. The four principal Unix RISC vendors -- Sun, HP, IBM, and Digital -- have not only converged their OS offerings so that they are substantially similar, they have also dramatically improved the quality of their products (see the table Unix operating systems converge, page 60).

Diversity -- the spice of open systems -- does remain, fortunately, as each Unix vendor seeks to add value and differentiate their offerings. The level at which differentiation occurs is steadily rising out of the Unix kernel up to higher level issues, such as systems management and high availability. In this article, we take a closer look at the various flavors of Unix from the major system vendors to support our claim that the OS is stable and ready for commercial acceptance and application. And we discover just what features the vendors now claim are their trump cards for differentiation in a standardized world.

Unix converging out of chaos
Selecting the best OS for any environment, application, or user is inherently idiosyncratic. We sometimes disregard the objective facts and rely on our preferences and prior experiences. This is particularly true in the Unix marketplace, in which each of the four major vendors have skeletons in their closet that feed lingering negative impressions told and retold by armchair Usenet historians.

The earliest releases of IBM's AIX, for instance, were very unstable. HP-UX saw tough times, too, especially when HP first attempted to implement the OS on Apollo's PA-RISC architecture. Digital's on-again, off-again romance with Unix (remember Ultrix?), together with its pre-Alpha market downslide, left many potential customers weary, if not wary. And most recently, SunSoft dragged much of its customer base through muddy times as the company yanked its operating system from its Berkeley (BSD) roots and replanted it in the more fertile marketplace for SVR4-based Unix. It took several revisions for SunSoft to achieve an SVR4 version (Solaris 2.3) that finally equaled the reliability and speed of its predecessor, the well-respected SunOS 4.1.3. Not until late last year did the long awaited Solaris 2.4 step beyond that standard bearer when it shipped in October.

Today, all four RISC vendors offer excellent and stable Unix OS alternatives with very similar feature sets. Digital's OSF/1 version 3 (renamed Digital Unix 3.2 in March of this year), IBM's AIX 4.1, and SunSoft's Solaris 2.4 were all released in the latter half of 1994. In 1995, HP begins the transition to HP-UX 10.0 in two major phases -- the New Business Release that should ship about the time this story appears and the General Business Release, scheduled for this fall.

Solaris is constructed from a true SVR4 code base. HP-UX and AIX originally licensed the System V, release 3.x code set, but did not subsequently license SVR4. HP and IBM have however, invested in bringing their Unix kernels into substantial compliance with SVR4. Digital is the one founding member of the Open Software Foundation (OSF) to enthusiastically adopt the operating system produced by OSF.

All four of these vendors are well on their way to implementing X/Open's Single Unix Specification, formerly dubbed SPEC 1170 because it details 1,170 APIs and interfaces (see table Unix operating systems converge). All now support the POSIX shells and utilities specification (1003.2), real-time kernel extensions (1003.1b), and revision 4 of the X/Open Portability Guide (XPG4), which is a superset of POSIX specifications. IBM's AIX 4.1 complies with the base levels of revision 3 of the System V Interface Definition (SVID 3), but not all levels, and technically does not support all of SVID 3.

To date, SunSoft is the only one of the four major vendors to pursue a multiarchitecture OS strategy. Solaris 2.4 unified the source code of its SPARC and Intel-processor versions of the OS, and a PowerPC version of Solaris is nearly ready to go, awaiting the official shipment of IBM's Power Personal Systems. And because SPARC-compatible hardware vendors like Tatung and Axil Computer provide additional platform choices for Solaris users, the OS cannot be considered in a vacuum from its sole supporting hardware infrastructure.

Digital Unix stands apart from other Unix options because it is a 64-bit, not 32-bit, OS that takes advantage of the 64-bit Alpha architecture. A 64-bit chip and OS pays substantial dividends in integer/floating-point performance, and has advantages in processing large files. Sun and HP have laid out a road map for 64-bit CPUs, but for now Digital is out in front by itself.

SMP, threads, and clustering
With the release of AIX 4.1, IBM, with substantial help from Groupe Bull, joined Sun, HP, and Digital in providing OS support for symmetric multiprocessing (SMP), a multithreaded kernel, and user-level threads so developers can optimize application software for SMP environments.

SMP and threads implementations are a bit like wine -- they improve a great deal as they mature. SunSoft wrote most of SVR4's base multiprocessing code and has devoted years to multithreading its libraries. HP also has been working on SMP and threads since 1991. Digital says one of the primary reasons it adopted OSF/1 was that its modular kernel design made it east to swap in new components, and SMP capabilities was at the top of their list.

All four vendors will tell you that their OS subsystems are multithreaded, but there is a real difference between libraries and subsystems that exploit multithreading. In particular, threads come in greater and lesser granularity. Finer granularity means higher performance, both on SMP and uniprocessor systems, by enabling applications to better manage I/O, so that a CPU does not stall as much on a disk or network transfer or even a medium-sized memory access.

The four vendors also support CPU clustering for high availability, and to varying degrees, for performance. Here the table tips away from Sun and HP. IBM is favored with what many consider the most mature clustering solutions, its HACMP and SP systems, followed closely by Digital. HP and Sun are the relative newcomers.

Support for clusters crosses well over the line from OS to hardware issues. Although all four vendors have introduced new or improved cluster support recently, suffice it to say that all are specialized applications of the firm's Unix OS. One OS-specific clustering note comes from Digital, which said it is porting its VMS clustering lock manager -- an important feature for database performance and integrity -- to Digital Unix.

Filesystem enhancements
Early AIX implementations also raised the bar for Unix OS by including a Journaling File System (JFS). Log-based filesystems like JFS will soon become a de facto standard because it simply takes too long to boot a Unix system and perform a standard filesystem check (fsck) on very large files, such as those typical of business databases. Booting a 1-gigabyte filesystem, for example, can take 10 minutes. A log-based filesystem can do that in a few seconds, because all it needs to do is read the log, or journal, off disk. Booting a 5-gigabyte JFS system, including disk and memory checks, for example, happens in about two minutes.

In time, the other vendors will match IBM's JFS capabilities. IBM bundles its JFS with both server and desktop systems, as does Digital with its AdvFS (Advanced File System). SunSoft's On-line Disk Suite is now bundled with Solaris server packages, but not desktops. HP's On-Line JFS is strictly an add-on.

IBM also set the pace when the company implemented a related but distinct set of capabilities in its Logical Volume Manager (LVM). Volume management generally refers to the ability to increase or decrease the space allocated to a filesystem while the machine is still up and running, and enabling large files to span multiple physical storage devices. These capabilities, together with mirroring and striping, are included in Sun's On-Line Disk Suite, and HP's On-Line JFS. Digital's Logical Storage Manager (LSM), an add-on product, provides its volume management, mirroring, and striping. Mirroring is crucial for a JFS, because the journal contains all the meta data on the contents of the filesystem.

AIX 4.1 also has "on-the-fly" file compression and decompression, which again sets it apart. AIX is also the only OS in this group to bundle the Andrew File System (AFS) as an option to Sun's pervasive NFS technology. AFS is available for Solaris, HP-UX, and OSF/1 from third parties.

System and network management
The system and network-management arena remains a hot contest among the major Unix vendors. AIX deserves credit for making an early commitment to core system-management tools that non-experts could easily use -- reminiscent of its mainframe tools that are administered mostly by clerk-level personnel. Innovations in Unix system and network management are not far off on the horizon, and no one Unix vendor lags far behind in the group, although third-party products lead the pack (see the "Network-management innovations," September 1994 and "The changing needs of system management," March 1995).

On the system management front, all the operating systems now have graphical, point-and-click interfaces and enable software installation from a central network location. In early January, Sun took a big step forward with its Solstice management architecture road map, and will soon, if not already, be shipping the product. Sun's Encompass network management platform, which is part of Solstice, breaks new ground by providing a distributed object-based network management platform.

Sun's SunNet Manager is the network management leader by shear numbers, but, HP's OpenView is fast becoming the most respected, if not leading, network-management platform. IBM's NetView/ 6000 began by using licensed OpenView code, but has evolved considerably since that time. Digital's PolyCenter is an OEM version of IBM's NetView/6000.

Object objectives
Object-oriented OS layers remain a horizon issue for most users -- one that is watched carefully, but which few have adopted fully. All four vendors currently have distributed object plumping in their systems and object request brokers (ORBs) -- the middleware components for object distribution -- based upon the Object Management Group's Common Object Request Broker (CORBA) specification version 1. All the major vendors are committed to complying with the version 2 specification when it is completed sometime soon. What will run on top of their respective ORBs, however, sets the vendors apart.

IBM and HP are both backing (in dollars) Taligent, a darling in the media for its planned object technologies innovations. Taligent recently backed off its original goal of creating an object-based operating system, but remains committed to a comprehensive object framework, development, and user environment. The object framework should ship later this year.

Sun broke new ground in cooperation with NeXT Computer, and Digital has recently signed on to back the resulting OpenStep object APIs. OpenStep is a set of programming interfaces lifted out of the NextStep operating system, and as such, benefits from real world experience. Sun and Digital expect to ship OpenStep and a object development toolset by midyear.

Seen one, seen 'em all
The Unix OS market has changed. No longer are there numerous fundamental differences between implementations. Rather, the battle ground shifted to higher-level issues, such as network and system management and objects. Moreover, each of the major vendors continue to carefully monitor the competition and appear ready to license, duplicate, and leapfrog good ideas.

For users who think their needs are not well served by the direction of the core hardware/software vendors, a wide variety of options are served up by independent Unix OS vendors. The SCO, still the volume leader among independent OS vendors, is broadening its multiuser host system focus and adding a "Windows-friendly strategy" where it hopes to secure a bigger role as a server to Microsoft Windows 95 desktop users (see sidebar SCO does Windows see sidebar). Other options include NeXT Computer's NextStep for object-oriented enthusiasts, Novell's UnixWare for those most concerned with serving NetWare desktops, and Berkeley Systems Design's BSD/OS for those who refuse to accept the pollution of Berkeley Unix with System V release 4 (see sidebar Alternative flavors of Unixsee sidebar).

About the author
Barry Bowen is a computer industry analyst and writer with the Bowen Group Inc., based in Bellingham, WA. He focuses on client/server, re-engineering, and Internet issues. You can contact him at barry.bowen@advanced.com.

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Windows NT looms ever still

Although it is not Unix, nor is it a strong contender as an "industrial-strength" operating system (yet), we'd be foolish not to acknowledge Microsoft's Windows NT for its Unix-like features, if not for its potential as a Unix replacement. Windows NT is, of course, a whole different ball game for Unix developers. NT is compliant with POSIX 1003.1 -- and some of revision 3 of the X/Open Portability Guide (XPG 3) -- but not enough to be fully compliant. The other high points of NT's Unix similarities are its support for DCE's RPC calls and its TCP/IP network client utilities, such as ftp, telnet, rsh, and rexec. NT also implements the streams protocol environment, which it used to support TCP/IP and Novell's SPX/IPX.

Third-party firms also are developing sets of Unix utilities to run on Windows NT, but those will primarily assist technical users and will not fundamentally improve the portability of Unix applications being moved to NT. Portability issues include significant differences in the socket library sitting underneath the RPC mechanism, no native support for X Window, Motif, or the Common Desktop Environment, and no native analogue for the Unix fork() and exec() function calls.

Users will find NT is a preemptive multitasking environment, so within a Windows interface multiple applications can be run in a far more natural fashion than Windows 3.x. Unix users are likely to be frustrated, however, by NT's lack of an automount analogue, which makes accessing resources on a network a far more manual process. And, as distributed object technology moves forward, NT is likely to pursue its own path. So far, Microsoft has shown no willingness to adopt CORBA or to articulate a vision for a distributed version of OLE (Object Linking and Embedding) -- both necessary steps to ensure object portability and interoperability.

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SCO does Windows

The Santa Cruz Operation's SCO Open Server operating system is the volume leader among independent Unix OS suppliers. Open Server was developed from a System V, release 3.2 code base, but has been updated so it supports SVID 3 and relevant POSIX specifications, compliant with XPG 3 and 4. SCO is also on track to support SPEC 1170. Consistent with the trend among Unix vendors, Open Server has implemented a journaling filesystem, and permits users to dynamically increase filesystem size, but not to shrink filesystem sizes. SCO also is in the process of implementing both the Andrew File System (AFS) as an option to NFS, and a CORBA implementation, although the company has not yet articulated what development environment it plans to offer for CORBA-based applications.

Open Server isn't often included in discussions of "industrial strength" Unix flavors because it runs on non-RISC (Intel processor) systems and, until recently, SCO's primary corporate focus has been multiuser host systems. The firm, however, has been carefully adding components and options that will enable Open Server to dish out files, print services, and operating system functions to Windows- centric desktop users.

In 1993 SCO acquired IXI, maker of the popular X-desktop environment and the lesser known Wintif, a client application for Microsoft Windows users that translates Motif application interfaces running on Open Server so they appear as Microsoft Windows interfaces on PC client desktops. In 1994, SCO also purchased the VisionWare company for its PCX server and SQL Retriever products. And SCO licensed Microsoft and AT&T's advanced-server technology, enabling Open Server to directly support LAN Manager environments, including Windows NT clients.

Now that SunSoft has brought its Intel-processor version of Solaris up to 2.4, SCO will finally face competition in 1995 from a mature Unix player that has both a modern Unix OS implementation and mainstream Unix credentials. It will be interesting to see how things unfold this year.

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Alternative flavors of Unix

There are many Unix and Unix-like operating systems to choose from. Three that offer unique strengths are NextStep from NeXT Computer, UnixWare from Novell's Unix Systems Group, and BSD/OS from Berkeley Systems Design.

NextStep is an important operating system because Unix developers looking forward to object-based application environments can get started now on a variety of hardware architectures. NextStep is a mature object system, particularly its development toolsets, and NextStep's class-based APIs, in the form of OpenStep, will soon be components of Sun and Digital's Unix OS. Native NextStep currently runs on Intel-compatible systems, HP's PA-RISC workstations, and newer Sun SPARC workstations.

Developers will, however, have to cope with NeXT's proprietary object request broker (ORB), called PDO, and NeXT's strong bias toward Objective C, rather than C++ or Smalltalk. NeXT has committed itself to implement a CORBA 2.0-compliant ORB when that specification is finalized. And NeXT's multiplatform strategy makes it likely that they will offer translation utilities between Objective C and other development languages.

Novell's UnixWare 2.0 is an Intel processor-based of SVR4 implementation with numerous extensions to interoperate with NetWare clients and servers. It also runs many application binaries written for SCO's Open Server and Open Desktop, as well as SVR4 binaries that do not call vendor-specific libraries.

UnixWare is a multithreaded SMP operating system. It has a journaling filesystem with support for mirroring and striping and dynamic filesystem resizing. Extensions to support CPU clustering are in the works for 1995.

The UnixWare OS provides many conveniences for NetWare environments, including compatible file and print services, and NetWare's unusual mail-handling system. Full support for NetWare directory integration is promised for the next release (version 2.1). UnixWare also supports all the standard Unix networking and communications facilities, including NFS, NIS, SNMP, and standard Unix mailers. UnixWare does not yet support NIS+.

For developers and users who believe the move from Berkeley-based Unix to SVR4 is a bad idea, there's BSD/OS from Berkeley Systems Design. It has both Intel and SPARC solutions. Perhaps most importantly for mainstream workstation users, the SPARC-based version is binary compatible with SunOS 4.1.3. Sun Microsystems users disenfranchised by the move to Solaris will, therefore, have a source for continued OS enhancements.

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