Hi Chuck, Lou did reach out to me and shared a copy of his document. (If you read this Lou, thank you!) I haven't yet, but I plan to go through it and learn (I know I will) lots of good stuff. I did come across the thread you mention with your spreadsheet and I also plan to make good use of it. Thank you for sharing it in that thread!
I have an RD32 drive that has been working fine, but recently developed some sort of problem that now prevents me from even formatting it. It starts out just fine, encounters a couple of bad blocks and then stalls the formatting process. I have another drive that isn't DEC standard so that's where patching of ZRQCH0 on my XXDP tape comes into place. I'm guessing you're right, I may have to abandon the idea of using the real drives and get something like a Qbone or something. Is there such a thing as an MFM drive emulator that would plug in to the RQDX3 as a real drive would? Back in the 80's I came close to getting an 11/23 with a couple of RL02 drives and I think some RX-drives as well. Probably a tape drive too. But unfortunately it fell through. So this is an attempt to get to tinker with the real thing. I love the SIMH simulator suite but for some reason, missing the hardware takes away a big part of tinkering for me. So I am enjoying having these 11/23+ boards and drives to tinker with now. Thank you for all the information, tips and pointers! -Peter On Sun, Oct 27, 2024 at 1:55 AM Charles Dickman via cctalk < [email protected]> wrote: > Search the list back in late 2018, there is a thread with the same subject. > > There is a link to a spreadsheet in that thread that has the calculations > for new drive sizes. > > Lou and I sort of worked out the details without knowledge of each other > and he had a nice document describing how to create a new entry in the > table. He seemed reluctant to share it at the time, so I will respect that > now. > > I was interested in modifying the tables so that I could create a maximum > sized disk to use with an MFM disk emulator. > > Congratulations if you have an MFM drive that you think is reliable enough > today to format and try to use. The central theme of the RQDX3 format is > bad block replacement, and you will probably need it. > > Based on the reliability of the drive, a portion of the drive is allocated > to bad block replacement. One sector per track (?) is reserved for in-track > replacement and a group of tracks are allocated for out-of-track > replacement. The space allotted for replacements is inconsistent, for > example the RD51 has room for 0.66% of the blocks to fail vs. the RD33 > which can only tolerate 0.19% block failure rate. The replacement block > locations are based on a hash. The only place I have seen the replacement > algorithm documented is in an Ultrix driver for the microVAX 2000 (?). This > would make a sector image of an RQDX3 drive very difficult to work with > unless it is connected to another RQDX3 or the replacement map is > understood. > > Is Lou around? I hope so, he refined a PDP-8/e memory board design I did > and built multiple copies. That phrase used to imply moving on to some > other hobby, but lately these old computer lists it's become past on. Ugh. > > -chuck > > If the original author is no longer available to ask I can contribute my > copy to bitsavers. This has been a topic of discussion for many years. I > doubt DEC/Compaq/HP cares anymore. > > > > On Thu, Oct 24, 2024 at 5:34 PM Glen Slick via cctalk < > [email protected]> > wrote: > > > Did Lou ever publish somewhere his notes on patching ZRQCH0? > > > > Back from around almost 10 years ago: > > > > > > > https://forum.vcfed.org/index.php?threads/patching-zrqch0-to-use-any-geometry-mfm-hard-disk-on-rqdx3.39318/ > > > > Is Lou still around? Looks like he hasn't posted on VCFed in a few years. > > > > > > On Thu, Oct 24, 2024 at 11:45 AM Jacob Ritorto via cctalk > > <[email protected]> wrote: > > > > > > I don't have the source, but I had great success octal-patching my > copy a > > > few years ago, made it work with a Maxtor xt-11something instead of the > > > real rd54 / xt-2190. > > > I'll reply again if I can find the instructions for doing it. Just > > > followed recipe from some guy's website and it worked perfect. > > > > > > On Thu, 24 Oct 2024 at 09:20, Peter Ekstrom via cctalk < > > > [email protected]> wrote: > > > > > > > Hi everyone, > > > > > > > > Does anyone have the source for the ZRQCxx formatter? I have found a > > pdf > > > > for ZRQCE0 but am curious if the actual source code for that one, or > > ZRQCH0 > > > > is available? I'd like to make some changes to the UIT table. > > > > > > > > -Peter > > > > > > >
