[johnnym]

Short of any other results, I did check my inventory for maybe compatible buffered/registered ECC DIMMs and though some didn't work, some did indeed work - at least for the time frame I tested them!

I don't remember where these two originally came from, but they did work in my PWS 500au and it survived both kernel boot (Linux 6.x) and operation (7za b -md=2m, openssl speed -elapsed) with them installed:



Those are CENTON CCB256M/REG133, though not identical modules (different PCB revision and different SDRAM chips). Unfortunately I couldn't find anything about them on the WWW, neither could I read out their SPD EEPROM for their timings from the PWS nor from a DL380 G2 and I think I don't have any other systems that can use those DIMMs, except maybe my Blade 100. But I doubt I can read the EEPROM there with Linux. So yeah, those are buffered ECC PC133 modules with 256 MiB each and they worked for me.

In addition I did pull two from each of the following buffered PC133 256 MiB DIMMs out of another DL380 G2 and all of them worked, too, i.e. same as above: kernel boot OK and operation OK with all of them installed (first pair in DIMM slots J1, J2 (bottom ones, see the DIGITAL Personal Workstation 433a Upgrade Guide (EK–ALMIA–KU. A01) pages 14 and 15 for details) and so forth):



The top and bottom ones have a HP/COMPAQ part number 127005-031 and are:

* top: hynix HYM71V32C735HCT4-H PC133R-333-542
* bottom: Micron MT18LSDT3272G-133E1 PC133R-333-542-B2

The middle one is actually also a Micron MT18LSDT3272G-133E1, though with PC133R-333-542-B1 instead. It has a HP label attached with (specification?) D8266A.

Here's what you see on the system console and in SRM when all of these are installed:

Code:

ff.fe.fd.fc.fb.fa.f9.f8.f7.f6.f5.CPU 0 speed is 2.00 ns (500MHz)

ef.ee.ed.ec.eb.f4.ea.e9.e8.e7.e6.
ewa0: link up : Negotiated  100BaseTX: full duplex
e5.e4.
Digital Personal WorkStation 500au
Console V7.2-1 Mar  6 2000 14:47:02
>>>
>>>show config

Firmware
SRM Console:    V7.2-1          Mar  6 2000 14:47:02
ARC Console:    5.70
PALcode:        OpenVMS PALcode V1.20-16, Tru64 UNIX PALcode V1.22-18
SROM Version:   v5.90

Processor
DECchip (tm) 21164A-2   Pass   500 MHz  96 KBytes SCache
2 MB BCache
PYXIS ASIC Pass 257

MEMORY


Memory Size = 1536Mb

Bank      Size/Sets   Base Addr
------    ----------  ---------
   0        512Mb      00000000
   1        512Mb      20000000
   2        512Mb      40000000


BCache Size = 2Mb

Tested Memory =  1536Mbytes
[...]

NICE! I think I'll continue to use these modules for my PWS 500au. 

I also found another compatible DIMM type when disassembling one of my IBM B50s. Those are buffered PC100 256 MiB DIMMs from IBM which work the same way as the six modules above and also together with four of those six modules above. They are stacked DIMMs, so actually have twice the amount of SDRAM chips on both sides:



IBM FRU number is 01K1142 labelled PC100 322-622R

As written above I didn't use all or most of the memory when testing with 7z. But I might give that a try when I find the time.

Apart from that all these DIMMs worked much more stable than anything else I tested, except for the non-buffered ECC modules that did equally well and which were installed prior to these ones.

---

So to sum that up, the following buffered ECC DIMMs work in the PWS (500au):

• CENTON CCB256M/REG133 (256 MiB/PC133)
  
• HP/COMPAQ 127005-031 (256 MiB/PC133) (see next post)
  
• HP D8266A (256 MiB/PC133) (see next post)
  
• IBM 01K1142 (256 MiB/PC100)