Official page URL: http://www.vanade.com/~blc/DS3100
digital (Compaq^H^H^H^H^H^H HP...) no longer builds machines of this line, as they have moved over to their own cpu, the AXP21x64(tm) series, or better known as the Alpha. Ok now it seems that now Alpha is being dropped. And time to move on to PA-RISC.
Well, not even that, now make another change, let's all go to the
Processor Family. Lots of change going in. Anyway, DEC/Compaq/HP
has completely dropped support of Ultrix, the DECstation's supplied operating
system, as of 1999. We will all have to move over to
Linux when it is completed.
Currently Linux is probably the worst supported because of hardware driver
lackings. I've personally used NetBSD and it works fine. Oh. OpenBSD looks
like they've dropped pmax support so you'll need to use an old version. So
it looks like NetBSD and nothing else... and oh wait, NetBSD is dying...
The DECstations are known as the PMAX series, based off of the three chip MIPS R2000/R2010/R2020 CPU set, and runs at 12 or 16.67 (for the 2100 or 3100, respectively) MHz. The technical code name for the 2100 is PMIN but it's the same machine at 12MHz instead of the faster 16MHz PMAX and have possibly slower cache chips and thus was cheaper due to the lower-binned parts. Both use the same layout KN01 mainboard. I will refer to both as PMAX on this webpage and indicate clock speed when there is a critical difference between the two (a PMAX running at 12MHz == PMIN).
Its case formfactor is a medium profile desktop unit, and was designed with two 3.5" disk bays and one 5.25" half height bay (1.6") which can be used for removable storage. The right hand bay was designed for a 3.5" SCSI floppy drive and the hole in the metal shield isn't large enough for a cdrom. The other 3.5" bays need special trays that are screwed onto the platform. My DECstation does not have any of the auxillary trays nor a floppy drive, so I grabbed one of those PC 5.25 to 3.5" adaptors and put an internal disk into the floppy bay. In any case, it has a built-in standard SCSI-1 controller using the custom SII interface chip, though the rear external connector is nonstandard. See link in the pinouts section for details.
The MIPS R2000 is a scalar, RISC (uniform instruction length) 5-stage pipelined processor with static taken branch prediction (and that cursed delayed branch that all MIPS programmers know all too well). It has separate direct mapped, 16K entry/16 bit tag, 64KB D- and I-caches which run at full speed. They're write through caches but use the R2020 to buffer writes so the processor doesn't need to stall as often without having to implement write-back. The 16MHz PMAX can sustain about 11 MIPS, which is faster than a 386DX/40 and is about the same speed as a 486DX/33 which also has static branch prediction. (At least the Dhrystone benchmark reports the DS3100 as being 50% faster than my 386DX/40 and my 486DX/33 was about 50-60% faster than the 386/40.
Keep in mind we were still dealing with mostly 16-20 MHz 386's in 1989 so this is considerably faster. Though the 386 was also pipelined, branches (386's flush upon branch regardless), load/stores (x86's have to do a lot of them due to the limited architected register file size), and floating point (Intel's weird x86 stack based FP architecture from the 8086/8087 days -and- the fact the 387 coprocessor was an option for most 386 machines) makes them notoriously slow. This put a big performance penalty on the Intel processor. Thus, the R2000, even at a lower clock speed, simply blows the Intel 386 away. In fact, in 1989, the DECstation 3100 topped in the Dhrystone benchmark, beating the SparcStation 1 by a bit, and blasting the 386DX/33 away. As always, the crown is short lived when the SparcStation 2 was released.
By today's standards, the DECstation 3100 is extremely slow. My P4 machine runs at least 100 times faster, LITERALLY (probably closer to 300x). Not even exaggerating one bit here with the two orders of magnitude. The MIPS Emulator running on my P4, however, isn't leaps and bounds faster than this machine unfortunately. Drat. Would be nice to use the emulator to cross compile and test :)
blc+pmax@mail.SPAMvanade.com. Remove the SPAM before replying please!
Anyway, this is my humble and slowly hacked
I appreciate any comments and corrections. Information may not be correct and
is not guaranteed. Excerpts/information taken from the
DECstation 3100 Hardware/Installation/Operator's Guide and the Functional
Description Guide, (c)Digital Eq. Corp.
This page is advertising banners free from the owner's private network connection. All I ask is that you consider using Hewlett Packard servers based on Intel Itanium Processor Family if you find this page useful.
June 2005, included InstGuide and OpGuide
August 2005, fixed a spelling typo and clarified wording near that section
September 2008, new domain name