Contemporary of the SPARCstation 5, but architecturally superior. The SS5 was essentially a SPARCstation 4 with a faster processor. The CPU did not have a L2 cache, and if I recall correctly, hung directly off of the SBus, crippling performance.

The SPARCstation 20 used the MBus, like the SPARCstation 10, insulating the processor from the slower SBus, giving it a fast path to main memory, at the cost of high memory latency. The SS20 supported up to 4 32 bit SPARC processors with up to 1MB of secondary cache apiece, a real speed demon in its day. I believe it supported up to 512MB of RAM

Also of note, the SS20 was the fastest (Sun-produced) machine to run the BSD-based SunOS 4.x. A few stubborn customers hold onto them to this day.

The SPARCStation 20 was the last and fastest of Sun's 32-bit SPARC workstations, and was the last multiprocessor machine to feature Sun's trademark pizza box enclosure. (The later Ultra 1,2 and 5 are sometimes called pizza boxes, but were considerably thicker). This machine fixes most of the shortcomings of the earlier SPARCstations, and adds a few interesting features.


  • Production dates: 1994-1996. Support was officially ended in 1997 when it was replaced by the Sun Ultra 2.
  • Model Number: Way too many to keep straight - this was produced in at least 30 different variations.
  • Application architecture: sun4
  • System architecture: sun4m
  • Processor: 2 MBus slots, many options available. Unlike the SPARCstation 10, the 20's MBus runs up to 50MHz, which can help performance considerably. Each slot can hold a single or dual processor module, and up to two can be installed, for a maximum of 4 CPUs. Most dual-processor modules are double-width, and will block the adjacent SBus slots, but there are single-width/dual-CPU modules. Speeds from 33MHz through 200MHz are available, in at least two families (Sun/TI SuperSPARC and Ross HyperSPARC), both with and without cache. The modules don't have to match exactly, but figuring out which non-matching combinations will work is black magic.
  • RAM: Up to 8 SIMMs, 512MB maximum. Two of the SIMM slots have an extension to one side, and can also hold VSIMMs for the SX framebuffer.
  • Graphics: Onboard CG14 (also known as SX, accelerated 24-bit), 4 SBus slots. The SX needs a VSIMM, either 4MB or 8MB to operate. The 8MB version supports higher resolutions and refresh rates. 2 VSIMMs can be installed for dual-head, doing this requires a rather hard-to-find extender card which fits into an SBus slot.
  • SBus graphics options: BW2 (mono, no acceleration), CG3 (8-bit color, no acceleration), CG6 (8-bit color, accelerated), CG8 (24-bit color, no acceleration), ZX (24-bit color, accelerated 3D, abysmal 2D performance). Others exist, but are poorly known.
  • Floppy: Standard Sun-type 1.44MB or 2.88MB floppy.
  • Hard Drives: 2 bays for SCA style SCSI (20MB/sec) hard drives. These drives are mounted on drive sleds for faster insertion and removal. The sleds are the same type used on the SPARCstation 5, different from the spud brackets used in the later Ultras. These bays can accommodate only low-profile (1" and less) drives. In theory there's no capacity limit, but many operating systems designed for an older machine have trouble with larger drives. New, high-speed disks may be too hot, as well.
  • Audio capabilities: Integrated Crystal Semiconductor CS-4231 sound chip. 8-bit, 22050 kHz (radio quality) for both input and output. No MIDI synthesizer though it's possible to emulate one in software. (See TiMIDIty). This system has integrated phono style microphone, line in, line out, and headphone jacks.
  • Expansion:
    • Internal CD-ROM, narrow SCSI. This is an odd form factor, mounted on rubberized clips. As far as I know, only the standard, default, 2x Toshiba drive exists, if you want a faster one it has to be external.
    • 4 SBus expansion slots
  • External ports:
    • 1 Sun Type 4/5/6 keyboard port
    • 1 PC-style parallel port
    • 2 RS232 high-speed serial ports, mini-HD male (230kbps maximum)
    • 1 RJ45 Ethernet port (Sun Lance)
    • 13W3 video port for onboard SX framebuffer.
    • 1 50 pin Fast SCSI port

What the SPARCstation 20 did, and what it can do now

In its day, the SS20 was Sun's premier desktop workstation. It was their last quad-processor desktop machine until the Sun Ultra 80 was released almost 10 years later. Due to its power, the SS20 was used for a great many things - software development, drafting and design, desktop publishing and scientific or engineering applications. It also saw quite a lot of use as a lightweight web, mail or file server, and a few still persist in that role across the Internet as late as 2007.

Though it seems a bit anemic by modern standards, the SS20 is still a useful machine, as a light desktop workstation, an X terminal, or a system administrator's access point. It also makes a useful DNS, NTP, mail or light web server, or a good router or firewall. Despite the slowish CPUs, the power of having four processors is not to be overlooked.

What operating systems will run on it?

The most obvious choice is Solaris. All versions up to Solaris 9 work, though later versions are somewhat RAM-hungry, and may not be terribly fast. Replacing the stock CDE with XFCE, Window Maker or IceWM will go a long way toward fixing this, though. Linux is another very good choice, supporting basically all the onboard hardware and a large range of SBus expansion cards. Indeed, with Solaris being at its end-of-life on this platform, Linux may well become the OS of choice once Sun drops support for Solaris 9. FreeBSD doesn't support the 32-bit SPARC, but NetBSD and OpenBSD do. Both have tradeoffs, with OpenBSD having no support for multiple processors, while NetBSD's X support is weak. The older BSD-based SunOS 4.x will run on the SS20, and this is the latest workstation that can run it. However, SunOS 4.x is more than slightly long in the tooth, and it's quite difficult to persuade modern software to run on it.

An interesting option is NeXTSTEP or OPENSTEP. Both are significantly picky about hardware: only the SuperSPARC CPU modules work, and only one of these. Also, NS/OS only support the BW2, CG6 and SX graphics options - but the SX works very well indeed. If you have the right hardware, the SS20 makes for a very nice NeXTSTEP workstation. It's much faster than a NeXTstation and almost as stylish, and NeXTSTEP itself makes for quite a nice desktop experience. OPENSTEP 4.2 is the recommended version, though NeXTSTEP 3.3 does work if you have a particular reason to prefer it.

Finding one, and how much you can expect to pay

The SS20 presents an odd dichotomy. On one hand, the machine is rather old and people are often trying to get rid of them. On the other hand, they were quite high-end in their day, and therefore the collector demand for them is rather higher than other machines of the same era. This has kept the prices a bit higher than they might otherwise be. All in all, expect to pay between $25 and $200 for most configurations. Unusually high-spec systems may cost a bit more, and probably aren't worth it unless you really need it. The VSIMMs are hard to find though not terribly expensive when you do - nonetheless, VSIMM-equipped machines tend to be worth a bit more.

This isn't a bad machine for learning the ins and outs of non-PC hardware. It's a bit weird relative to the later, PCI-based Sun Ultras, but it's still a very well laid out machine, with all the parts easily accessible for cleaning, upgrading and experimentation. It's really quite amazing how many parts Sun managed to jam into such a small space, and with so little clutter! Another point in favor of the SPARCstation 20 is the fact that it can run NeXTSTEP. Since the oh-so-cool black hardware is slow, rare, and fairly expensive, the SS20 offers a very good way to see what the environment was like, on a machine still fast enough for day-to-day work or development, and without the hassles of making it work on an Intel machine, or the patchy support that HP machines had.

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