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 <cctalk@classiccmp.org> 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 > <cctalk@classiccmp.org> 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 < > > cctalk@classiccmp.org> 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 > > > >
