This post is an introduction to the SPARCclassic hardware. It is a slightly idiosyncratic computer, even by Sun standards.
Removing the single lock-block screw at the rear of the chassis, allows the case to split into two pieces: the “top” containing the PSU plus drive-bays, and the “bottom” containing the PCBs.
Motherboard and I/O-Port board
Somewhat atypically, the rear ports on the system are not mounted on the motherboard, but rather on a separate rear I/O-Port board, which the main motherboard plugs into via a very wide edge-connector. The I/O-Port PCB is integral to the chassis (cannot be removed), but the motherboard can be removed.
This unusual arrangement was so that the exact same chassis could be used for both the SPARCclassic and the SPARCstation-LX – which had different motherboards but could plug into the same rear I/O-Port board. To separate the motherboard from the I/O-port PCB, there is large plastic “eject” lever that pokes up through a hole in the motherboard.
External I/O Sockets
- a DB25 socket providing a pair of RS-232 serial ports. Although 2 serial ports in a single DB25 socket might seem strange to PC afficionados, it is common on late-80s and early-90s Sun and compatible systems, and also some from other manufacturers.
- a mini-DIN8 socket for connection of an external Sun keyboard+mouse combination.
- 3.5mm analogue audio jacks, one for input, the other for output.
- an HD50 fast-narrow-SCSI socket.
- an HD26 socket that is described in detail below.
- a 13w3 analogue video connector for an external graphics screen.
- a DB25 parallel-port.
- an RJ45 10BaseT Ethernet socket.
- a couple of hidden other sockets, discussed below.
The SPARCstation-LX used the rear HD26 socket for 16-bit digital audio, to connect to an external Sun speakerbox; when the speakerbox is plugged in, the in-chassis analogue speaker is disabled. On the other hand, the SPARCclassic used the traditional separate analogue audio-in and audio-out jacks to support an 8-bit external audio capability.
But that’s not all: that very same HD26 socket also contains an Ethernet AUI (10Base2 attachment-unit interface) channel – if you plugged a special Sun-specific HD26-to-15-pin-AUI cable into that port, you could use an external transceiver to attach to a coax 10Base2 Ethernet.
And, of course, there was an optional external HD26-splitter cable that converted the single HD26 socket on the back panel into a pair of HD26 sockets – one for the speakerbox, the other for the AUI.
Although I have a couple of speakerboxes, these cannot be used on the SPARCclassic, due to the lack of on-board 16-bit digital audio on the motherboard.
As well as the abovementioned AUI interface, the SPARCclassic provides on-board 10 Mbits/sec twisted-pair Ethernet via a rear RJ45 10BaseT socket. Again, a 100 Mbit/sec SBus card could be added, but there is no way a 50MHz microSPARC could take much advantage of that (for their Fast Ethernet SBus cards, Sun recommend a minimum of a 60MHz SuperSPARC with 1MB L2 cache).
The Hidden Sockets
The SPARCstation-LX also had built-in ISDN network connectivity, via a pair of ISDN TE sockets on the rear panel next to the 10BaseT socket. The SPARCclassic motherboard does not have ISDN capability due to not having a DBRI interface chip, so Sun covered those rear ISDN sockets with a stick-on piece of beige plastic, presumably to prevent customers complaining that “the ISDN sockets don’t work”!
The microSPARC CPU+FPU
The microSPARC CPU was not originally intended for use in a computer/workstation – it was intended for embedded systems use such as in PABX switching systems, RAID controllers, automotive system controllers, very early set-top boxes, that kind of thing. However, in 1991, Sun was getting delayed with development of the general-purpose SuperSPARC workstation/server CPU, and expected pricing of same based on die-yields indicated that SuperSPARC wasn’t going to be economically viable for lower-end workstations. Sun thus needed to a quick-and-cheap-to-deploy alternative to tide them over in the entry-level workstation market. Thus the relatively-low-performance microSPARC was pushed into service in the SPARCclassic and SPARCstation-LX.
Quite apart from the simple in-order CPU pipeline, the microSPARC has a rather more significant performance problem: drastically undersize caches for running Solaris or SunOS, or indeed any other desktop operating system. Merely 4KB instruction-cache and 2KB data-cache, when workstation competitors were often 8KB+8KB L1 backed by an additional external L2 cache. On the plus side, in spite of it’s diminutive size, microSPARC included on-chip MMU, IOMMU, SBus controller and FPM-DRAM memory-controller, thus making the board level design much simpler and cheaper – ideal for a Sun “lunchbox” type enclosure. It really was the small low-cost option, all around.
The good news is that with the MMU, IOMMU and memory-controller on-chip rather than external, access-latency to main memory is low, which is a good thing considering how frequently main memory will be accessed due to the tiny on-chip caches.
Another quirk of the microSPARC is that the on-chip FPU is not a Sun, TI or Weitek design, but rather was a design licensed from Meiko Scientific, and turned out to be rather more efficient than earlier designs.
So where is the CPU hiding? There are several large clearly-visible ICs on the motherboard, but the tiny microSPARC CPU is hiding under the built-in mini-speaker, under it’s own plastic shroud:
We are going to have to be rather patient when using this machine, it really is rather slow. At 50MHz the SPARCclassic is, with a following wind, roughly equivalent in interactive feel to a previous-generation 40MHz SPARCstation-2. Let’s see what we can get out of it!
Internal Mass Storage
The internal drive-bays are located in the top segment of the chassis, next to the PSU:
The on-board mass-storage systems are (a) 50-pin fast-narrow-SCSI (10 MBytes/sec) and (b) traditional NEC/Sony-compatible diskette interface; each connected via a ribbon-cable to one of the drive bays.
The on-board SCSI is also routed to an HD50 connector on the rear panel, for connecting external SCSI devices such as a CDROM drive, external disk-pack or SCSI document-scanner.
Of course, you could add an SBus card to provide an alternate/additional storage interface, eg: a SunSwift card (fast-wide-SCSI 20 MBytes/sec) or
even a Sun Fibre-Channel interface card, although the microSPARC CPU would have difficulty taking much advantage of the extra bandwidth in either case.
The SPARCclassic has six 72-pin SIMM slots (yes: six, not a traditional power-of-two such as four or eight slots), which take 4MB or 16MB 70ns FPM modules with parity. ECC modules are not supported, nor are EDO modules.
The official maximum RAM capacity is 96MB, but there is a way of getting more in there, which will be discussed in a later episode.