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Unix operating systems compared

Our annual update on Unix (and Unix-like)
operating systems developments

By Barry D. Bowen

June  1996
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As the differences between vendors' Unix versions fade, other battleground issues have begun to pop up. The race is on to bundle more comprehensive Internet solutions, Java support, and graphical interfaces. We sort through the new developments. (2,700 words)

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Long the darling of the science and engineering communities, Unix operating systems continue to mature and earn respect in the business community. All of the major systems vendors now have "industrial-strength" versions of Unix that support high-availability, journaled file systems for faster recovery of very large systems. They also continue to push the envelope on file size, addressable memory, and the size of databases they can support. IBM's announced roadmap to brand its MVS mainframe operating system X/Open compliant put a stake through the heart of the argument that, somehow, Unix would never be ready for prime time 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 availability of sometimes wildly divergent flavors Unix from the various vendors created confusion.

For many, the confusion persists. Long-time Unix watchers, however, realize that the various Unix implementations continue to grow closer together, especially in light of most Unix vendors stating they would include a version of the Java Virtual machine in their operating systems. The functional reality today is that Unix operating systems closely mirror each other as they vigorously compete to improve performance, track new hardware and chip sets, and broaden the ease with which they support ever more sophisticated layers of commercial computing, system and network management, and Internet connectivity and commerce solutions. The differences that remain tend to be at higher levels of the OS.

Whether it's the result of their enthusiastic support for open, highly reliable, multi-vendor OS standards, or simply fear that continued fragmentation would marginalize Unix as a force in mainstream computing, Unix vendors are delivering on their long-standing promises to rally around more carefully defined and better implemented de facto and de jure standards. During the last year, for instance, the promised support for SPEC 1170 -- now renamed X/Open branding for Unix95 -- is a reality. Principle Unix workstation/server vendors -- Sun, HP, IBM, Digital, SGI -- all claim full support and say they are near final branding.

Unix, however, remains a competitive market. So for all the work being put in to make Unix OSes similar, firms also are trying hard to get a leg up on the competition. Much of that work, however, does not easily fit into check boxes on product spec sheets. How do you really quantify the work of a vendor when they say a new OS version includes three man-years worth of painstaking work to optimize various Unix subsystems? Bottom-line measure for many customers are reliability, performance, and ease of use. Reliability is now generally excellent for most vendors. Relative rankings of performance are constantly changing and improving. And ease of use is too subjective to address here.

During the last year, perhaps the number one technical differentiator to emerge among Unix OS implementations is 64-bit support. Digital's early trailblazing on the 64-bit path, increasingly accepted in market, has other vendors are responding. (See sidebar, Twice the bits.)

Far from the Unix kernel, or even crucial sub-systems, other battleground issues are shaping up over the bundling of more comprehensive Internet solutions, Java support, and more graphical interfaces to configure and manage the OS and its services. (See the sidebar, Today's Unix at a glance for a comparison table.)


Image makers appear successful
When we last compared Unix OSes in SunWorld Online's predecessor, Advanced Systems (May 1995), most major Unix vendors had skeletons in the closet that they were diligently striving to put behind them.

Early releases of IBM's AIX were unstable. HP was still waiting for its long-time customers to forget its labored attempts at integrating Apollo products into the PA-RISC and HP-UX flock. At the same time, it was promising the transition from HP-UX 9 to HP-UX 10 would be "seamless." And Digital's checkered Unix past -- remember Ken Olsen's "Unix is snake oil" comment -- still lingered as the firm struggled to recover from its pre-Alpha market dive. Sun Microsystems and its SunSoft operating system company had its own much-publicized travails as it pushed customers off its respected Berkeley-based OS to SVR4-based Solaris.

In this respect, a year has made a big difference in the Unix OS marketplace. Give vendors due credit for unveiling yet another round of OS upgrades without opening old wounds. Their image make-overs appear nearly complete, as the process was accelerated by an influx of recent Unix-converts not touched by past debacles, and the pleasant distraction afforded by Microsoft's troubles with Windows 95 and NT.

Digital's Unix has been renamed yet again, as OSF/1 version 3 was supplanted by Unix version 4. IBM's AIX version 4.1.1 has reached 4.2, and SunSoft's Solaris is in the process of becoming 2.5.1. In 1995, HP began the transition to HP-UX version 10.0 in two major phases, completing it with the February 1996 release of 10.10. HP is now working on a third-quarter release of 10.20. SGI is migrating users from IRIX 5.3 to 6.2. Data General shipped DG/UX 4.1 in the fall of 1995, and is looking at another release late this year when its NUMA (non-uniform memory access) Intel-based servers ship. (See sidebar, Today's Unix at a glance.)

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. SGI licensed both, but extended IRIX's System V compliance based upon the SVR3 code set. Digital is the one founding member of the Open Software Foundation (OSF) to enthusiastically adopt the operating system produced by that effort, but it has dropped the OSF label.

All major 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. All vendors 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.

SunSoft continues to stand out among Unix vendors with a true multi- architecture OS strategy. Solaris 2.4 unified the source code of its SPARC and Intel-processor versions of the OS, and 2.5.1 unified its PowerPC version with that same source code tree. That makes Sun the only Unix vendor to be truly multi-architecture and multivendor. Even the SPARC version of Solaris ships on several independently-designed hardware platforms, like those from Axil Computer and Tatung Science & Technology.

Data General is currently supporting both Motorola 88000 and Intel chip sets, but that is the result of a transition demanded by the shift in the firm's own server hardware. The 88000 is on its way out, and Intel will be its chip for the future.

IBM touts AIX as multi-vendor -- IBM, Motorola, Groupe Bull, and Apple -- but all those systems are PowerPC architectures. AIX also supports the Power and Power2 architectures, but those are proprietary to IBM as well.

Bundled ideals
Another strategy to differentiate OS offerings is to bundle functionality into packages. Bundling generally lowers the cost of add-on and middleware layers and gives the vendor the option of more tightly integrating the installation and management scripts.

SunSoft, for instance, now offers three server lines. They include the Ultra Enterprise server line based on its new UltraSPARC chip, the older SuperSPARC-based SPARC 1000 and 2000 class machines, and a range of desktop servers. Sun also offers turnkey servers including several workgroup server packages including PC administration, Internet, Applications, and a basic server to compete with SCO.

So, too, has IBM preconfigured various options. IBM offers packages for the Internet, Lotus Notes, communications, and systems management.

SGI and IBM are bundling more with their base operating system as well. With 4.2 of AIX, IBM includes a Web browser and Adobe Acrobat, for instance. SGI is throwing in a Web browser and Web server.

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 its list.

Data General and SGI have also been in the threads and SMP game for some time.

All major Unix vendors also support CPU clustering for high availability, and to varying degrees, for performance. Current support is limited in most cases to four-way clusters, with eight- and 12-way configurations planned for future releases.

File system enhancements
Early AIX implementations also raised the bar for Unix OS by including a Journaling Files System (JFS). Log-based file systems like JFS have now 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 one-gigabyte filesystem, for example, can easily takes more than 10 minutes. A log-based file system 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.

As HP, SunSoft, and IBM integrate more 64-bit support, file system size will grow. AIX 4.2, for instance, raises the bar from 2 gigabyte to 2 terabyte files systems, making a journaled file system even more essential.

AIX is also the only OS in this group to bundle the Andrew File System as an option to Sun's pervasive NFS technology. AFS is available for Solaris, HP-UX, and Digital Unix from third-parties.

System and network management
The system and network management arena remains a hot contest among the major Unix vendors, although most all the interesting technology remains in add-on packages.

AIX deserves credit for making an early commitment to core system- management tools non-experts can easily use -- reminiscent of its mainframe tools that are mostly administered 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.

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. Sun took a big step forward with its Solstice management architecture.

HP's OpenView remains the dominant network-management platform. IBM's NetView/6000 began with licensed OpenView code, but has evolved considerably since that time. Digital's PolyCenter is an OEM version of IBM's NetView/6000.

IBM also advanced its position in the marketplace by purchasing Tivoli's distributed management technology and plans further work to integrate it with SystemView and NetView environments.

Object objectives
Object-oriented OS layers are increasingly important for many users. Unix 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 version 2. What will run on top of their respective ORBs, however, sets the vendors apart.

IBM and HP both backed (in dollars) Taligent, a former darling in the media for its planned object technologies innovations. But Taligent is now defunct, and the object-oriented goals of IBM and HP are unclear.

Sun broke new ground in cooperation with NeXT Computer (now NeXT Software), and Digital also signed on to back the 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 has grabbed some of the more interesting developments from Taligent and integrated them into a more amorphous offering.

Seen one, seen 'em all
The Unix OS market has indeed changed. No longer are there numerous fundamental differences between implementations. Rather, the battle ground shifted to higher-level issues, such as 64-bit support, bundling, and network and system management. 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 Santa Cruz Operation (SCO), still the volume leader among independent OS vendors, is broadening its multi-user 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.

SCO also purchased the UnixWare group from Novell and entered into a partnership with Hewlett-Packard to jointly develop a next generation Unix offering. This endeavor has significant perils, however. The task requires engineers to deal with multiple code sets -- SCO's, HP's and UnixWare; multiple chip sets with PA-RISC and Intel; and, the transition to 64-bit computing. Indeed it will be a true challenge.

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Twice the bits; twice the fun

There is no doubt the most important core technical differentiation between Unix and other operating systems, and among Unix implementations, is 64-bit support.

Not only do all the major vendor put 64-bitness at the top of their discussion list, but so do independent analysts like Jean Bozman, IDC's research manager for the Unix and Server Operating Environments group.

Digital was faced with some tough choices a few years back and had to take very bold steps to remain a significant player. It blazed the trail in 64-bit RISC-Unix architectures and abandoned support for 32-bit applications in the process. As market demand has caught up to Digital's leap forward, so too are competitors.

SGI's IRIX 6.2 supports a dual-mode 64-bit and 32-bit functionality by using twin sets of shared libraries on its higher-end machines. HaL Computer is shipping its own 64-bit Unix variant for its own SPARC-based servers. And Data General agreed to port a 64-bit version of DG/UX to the SPARC platform, if there are clone and compatible vendors who want to buy it.

Sun, HP, and IBM have all taken a "go-slow" approach to 64-bit support. Bozman suggests these vendors simply did not need to set themselves apart from the field in a dramatic fashion and could afford to time their development to match rather than lead marketplace readiness. The top of their priority list is support for larger databases, where I/O, addressable memory, and database size are crucial for performance.

Whatever the reason, all three vendors are becoming increasingly specific about what they plan to do and when they hope to deliver on those goals.

SunSoft has been fairly specific with its 64-bit roadmap. Solaris 2.5 introduced 64-bit arithmetic, and 2.5.1 added 64-bit asynchronous kernel I/O to boost I/O performance. 64-bit file size and offsets are scheduled for early 1997, and full 64-bit kernel and file system is slated for early 1998.

HP is promising to disclose its detailed 64-bit roadmap in late summer or early fall. IBM is a bit more vague, but both are leaking details about promised progress -- current increases in support for larger file systems or file sizes, and promises for additional increases in 1997 and 1998.

It is perhaps meaningful to note that while Unix vendors argue over the schedule for 64-bit support, most point out that Redmond, WA-based Microsoft is still struggling to generate a scalable 32-bit NT server operating system.

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Today's Unix at a glance

What's changed in these operating systems in the past year

Solaris 2.5 and 2.5.1

HP-UX 10.10


Digital Unix 4

Silicon Graphics IRIX 6.2

Data General DG/UX 4.1

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Unix operating systems converge

[Yes] = Available. [No] = No announced plans.
Third-party = Definite third-party supplier.
Planned =There by end of 1996.
Planned 97-98 = Long-term plans..

System standards SunSoft
Solaris 2.5
HP-UX 10.10
AIX 4.3
Unix 4
Irix 6.2
POSIX 1003.1 [Yes] [Yes] [Yes] [Yes] [Yes]
POSIX 1003.2 [Yes] [Yes] [Yes] [Yes] [Yes]
POSIX 1003.1B [Yes] [Yes] [Yes] [Yes] [Yes]
XPG3 Base [Yes] [Yes] [Yes] [Yes] [Yes]
XPG4 Base [Yes] [Yes] [Yes] [Yes] [Yes]
SVID 3 [Yes] [Yes] [No] [Yes] [Yes]
Unix95 (SPEC 1170) [Yes] [Yes] [Yes] [Yes] Planned
64-bit Support
64-bit Hardware Compatible [Yes] Planned - 97-98 Planned - 97-98 [Yes] [Yes]
Full 64-bit OS Planned - 97-98 Planned - 97-98 Planned - 97-98 [Yes] [Yes]
TCP/IP [Yes] [Yes] [Yes] [Yes] [Yes]
SPX/IPX [Yes] [Yes] [Yes] [Yes] [No]
LAN manager Third-Party [Yes] Planned [Yes] [No]
Ethernet [Yes] [Yes] [Yes] [Yes] [Yes]
Fast Ethernet [Yes] [No] [No] [Yes] Planned
100VG anyLAN Third-Party [Yes] [No] [Yes] [No]
ATM [Yes] [Yes] Third-Party [Yes] [Yes]
Software router [Yes] [Yes] [Yes] [Yes] [Yes]
56KB direct interface [Yes] [Yes] Planned [Yes] [Yes]
Distributed computing
ONC-NFS [Yes] [Yes] [Yes] [Yes] [Yes]
ONC RPC [Yes] [Yes] [Yes] [Yes] [Yes]
NFS-Diskless [Yes] [Yes] [Yes] [No] [Yes]
DCE [Yes] [Yes] [Yes] [Yes] [Yes]
AFS Third-Party Third-Party [Yes] Third-Party Third-Party
CORBA [Yes] [Yes] [Yes] [Yes] [Yes]
OpenStep [Yes] [Yes] [Yes] [No] [No]
User interfaces
X11 R5 or R6 [Yes] [Yes] [Yes] [Yes] [Yes]
Motif [Yes] [Yes] [Yes] [Yes] [Yes]
CDE [Yes] [Yes] [Yes] [Yes] Third-Party
High availability
CPU clustering [Yes] [Yes] [Yes] [Yes] [Yes]
Journaled filesystem [Yes] [Yes] [Yes] [Yes] [Yes]
Dynamic FS resizing [Yes] [Yes] [Yes] [Yes] [Yes]
Mirror-striping [Yes] [Yes] [Yes] [Yes] [Yes]
Hardware platform
Intel [Yes] [No] [No] [No] [No]

[Yes] = Available. [No] = No announced plans.
Third-party = Definite third-party supplier.
Planned =There by end of 1996.
Planned 97-98 = Long-term plans.

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About the author
Barry D. Bowen is an industry analyst and writer with the Bowen Group Inc., based in Bellingham, WA. Reach Barry at