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Which came first ??

G

Gerardcjat

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Not about egg and hen ! :p

Yesterday, I was instructing myself about DEC / PDP SID Hard Disk. ( Which seems pretty large, size speaking, for that area ). Then a question arise :
How these drives related ** TIME FRAME WISE ** versus the smallest size ( DEC ) MFM drives ??
 
Gerard,

I think the first dec SDI drives / controller may predate the first dec MFM drive controllers (dec never made their own 5.25" MFM hard disks). I say this because although both are MSCP protocol, it seems to be that the UDA50 (Unibus SDI controller) manuals are often pointed to in later literature as a key reference about how to work with MSCP (mass storage control protocol).

So I have not looked at the dates on the print sets, but I think the UDA50 (first dec SDI controller) predates the RQDX1 (first dec MFM hard disk controller).

The service life of both however largely overlap, and maybe SDI was even longer. The RA7X drives were made into the 1990s by dec in Germany.

It apppears that SDI was replaced by DSSI, which was also MSCP protocol at the qbus controller end. I did a little research, and although there is a QBUS DSSI interface, it was not usually used on pdp-11 systems. I have read that it could indeed be used with pdp-11s though, looking like other MSCP disks. I have been tempted to try it, since the KFQSA qbus disk controllers appear on ebay at lower prices than SCSI, and the RF series disks show up more frequently than RA. The trick may be formatting the disk. Are there any XXDP diagnostics for KFQSA? I never looked, but it may have come out too late in the life cycle of the 11.....

Lou
 
Last edited:
Very helpfull reply. Thanks

Quote : I have been tempted to try it, since the KFQSA qbus disk controllers appear on ebay at lower prices than SCSI, and the RF series disks show up more frequently than RA

Please, let me know, as I have not decided yet which way I will go, Hard Disk wise.
As, I also enjoy very much "old stuff ", I may be tempted too .... May be more fun ( and more difficult ?? ) than SCSI way ?

( So far, I am inclined toward M7555 and MFM HD, mainly because I own that stuff but in an unknown state :(. Ref. my other post )
 
Gerard,

For sure, you should start with RQDX3. It is much more economical than SCSI, unless you already have the SCSI controller.

If you already own MFM disk drives, can you list for us which models? I can see if any of them match the standard dec RDxx geometries...

Lou
 
MFM disk drive : ST 4053 extracted from some kind of IBM PS/2 computer ( Not by me, By the vendor, so not that sure ... )

Another to come ( also in shipping state :wink: In fact, more precisely, I am waiting shipping aknowledgement from the vendor :confused:) : St-225

These are pretty common, are they ??

Have an MFM controller in an old PC, so, I may test them easyly , I think.
( In fact, I am working on that right now : ckecking the MFM controller card )
 
Gérard,

The ST225 is the drive that dec called RD31. They seem very robust. I have a couple of them.

ST4053 was not a drive that dec ever sold. It would be a good candidate for the procedure I developed to patch the RQDX3 low level formatter.

Indeed it is a very good idea to check the drives out on a PC. I have an old PC set up for doing exactly that. Once I have gained confidence in a drive on the PC, then I will work with it on the RQDX3.

Do you have an RQDX3 controller yet?

Lou
 
Yes, I have the RQDX3 board. Unknown state, but the is no reason(s) it shoud not be functionnal.
As you may see in another post, I experiment difficulties in restarting my OLD 486 PC. ( for MFM / ISA controller test ).
Life is not easy ;) but this is the fun !!
 
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