[jan-jaap]

So it has a dedicated servo surface on an inner platter.

Thanks, we'll see what comes of it in due time.

My 4D/70G was slightly different: the power inlet was a Hubbell twist-lock, not an IEC connector, the base compartment of the side tower had space for a tape drive, and there was a DC-37 port on the back for some unknown purpose (ESDI? Parallel?)

Initially the Professional IRIS shipped as the 4D/60 with the 8MHz R2300 MBC from MIPS. The R2300 relied on a VME ESDI controller and the CMC ENP-10 VME ethernet card. All Professional IRISes come with bulkhead wiring for ESDI and ethernet on the main tower. It is my understanding that ESDI wiring to the drive stack was external. I don't know if the tape drive of the 4D/60 was ESDI or something else (QIC-02?)

Then only 4 months later in July 1987, SGI announced the 4D/60T, the "turbo" upgrade for existing 4D/60 owners. This replaced the R2300 MBC with the 12.5MHz IP4 SBC. Complete systems were sold as the 4D/70, and a little later the 4D/50 with 8MHz CPU. Unlike the R2300 MBC, the IP4 board has SCSI. It is connected via the user-defined pins of the VME P3 connector and internal wiring to the drive tower. Additionally, there's a sticker on my chassis that says it's an "SBC CHASSIS".

Now, I imagine that if you replace a CPU board, you leave the rest of the system untouched as much as possible. So a 4D/60 upgraded with an IP4 to a 4D/60T would probably still use it's ESDI disk and doesn't strictly require SCSI. So one can speculate about the chassis of the original 4D/60. Did the "MBC CHASSIS" already have SCSI wiring? And what about the interconnect between the modules in the drive tower? With so little time between the R2300 and the IP4, the IP4 must have been under development before the 4D/60 was even released. So what makes an "MBC CHASSIS" -- ESDI wiring?

The twist-lock was for 110VAC countries I believe. The metal box with the circuit breaker and power inlet comes out easily and plugs into the wiring harness of the PSU. The harness itself is much more elaborate than most other systems. The PSU requires an external fuse, so there are three main power cables going to it: the top one feeds it from the power inlet, the bottom two go back to the circuit breaker. There's got to be a different circuit breaker in the 110VAC version as well (30 vs 15A). My more immediate problem is that the PSU doesn't switch on if I supply power directly and bridge the fuse. I would at least expect it to create 300+ VDC internally after the primary rectifier. I must be missing something.

I had it open to inspect e.g. electrolytics. There's a RIFA cap on the input filter that's cracked and I suspect a bit of leakage on the 12V output filter caps so I think it's prudent to replace them now that I'm in here anyway. But everything looks spotless and untouched -- it's like I unearthed a NOS Professional IRIS.



You can also see the 'intrusion detection' switch mentioned on Gerhard Lernerz's site and also in "This Old SGI" if I remember correctly. There's another on the main tower. If you open it the circuit breaker will trigger and kill power to the system