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Are there any 6 or 4 sector decpack disks?

G

gwiley

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Way back, on March 22, 2023...
Al Kossow said:
here are the timing specs for the diablo sync fields in a sector
header and data and bit order in the sector data are dependent on the format implemented by the controller
the information manual on the model 30 mentions 8-24 sectors are supported
quickly looking, i've seen 8,12,16 and 24 sectors used by various systems. 12 is used on pdp-11s, 16 on pdp-8s
Click to expand...
Is it possible that there are any disks with less than 8 sectors? Maybe 4 or 6 sectors? Based on Al's comment above, it seems like 8 is probably the minimum.
The RK05 emulator currently will emulate a minimum of 8 sectors. A modification to support as few as 4 sectors is possible, but not sure if it's worthwhile.
 
Maybe answering my own question here. Remembered a comment about number of sectors on another thread. On March 20, 2023...

Nevets01 said:
My Pertec D3000-series manual lists all of these as being available:
Code: 
6, 8, 10, 12, 14, 16, 18, 20, 24, 28, 30, 32, 36, 40, 42, 48, 56, 60, 64, 70, 72, 80, 84, 90, 96, 112, 120, 126, 128
I doubt any but the 12 and 16 were very common, but there's probably a few oddballs out there that use some of the others. Not sure how some of the larger ones would've been practical; would you even have enough space left for data in a 128-sector platter?
Click to expand...
 
gwiley said:
I doubt any but the 12 and 16 were very common, but there's probably a few oddballs out there that use some of the others.
Click to expand...
Custom Systems used 8 sector on Novas
IBM 1130 100tpi and 360/44 are 8 sector
Four-Phase 8231 is 16 sector
HP 7900A is 24 sector
Burroughs B1700 is 32 sector
 
Al Kossow said:
Custom Systems used 8 sector on Novas
IBM 1130 100tpi and 360/44 are 8 sector
Four-Phase 8231 is 16 sector
HP 7900A is 24 sector
Burroughs B1700 is 32 sector
Click to expand...
Thanks! This is exactly what I was curious about, other systems using this disk pack. It kinda seems like 8 sectors might be the minimum that someone would want to use with an emulator.
In the emulator, the size of the sector buffer is the concern. I could make it handle 2 or even 1 sector, but it requires some additional flexibility in how sectors are mapped to DRAM addresses. Not complicated, but it would be a change and need to be verified thoroughly.
On the upper end, there are only 4 sector bits output by the emulator. Would need to assign an extra (5th) address bit on the paddle connector to support more than 16. There are 3 spare drivers so this 5th address bit is a possibility if there's a need for it.

IBM 1130 was the first computer that I programmed (Fortran). IIRC, the disk capacity is 512,000 words
 
NF6X said:
I posted this over in the general minicomputer forum because I don't think it's DEC-related, but it might be of interest in this topic. I recently bought a pack which was advertised as an RK05 pack, but I think it's some other kind of pack. It doesn't use the same kind of sector/index notch skirt that I've seen on DECpacks and their relatives:

Click to expand...
As noted over there I believe that's a disc pack for an HP 7096A Disk Drive. It's 48-sectored (soft) but the timing track is held on a fixed disk platter on the same spindle. Don't think that @gwiley work could apply in the case of the HP 7906A Disc Drive, alas, since AFAICS the signal interface between the drive and the HP 13037C Disc Controller is their own brew.
 
Be extremely careful dealing with HP 2315 style packs.
The platters are not the same thickness between the 7900 and 7906
 
Al Kossow said:
Be extremely careful dealing with HP 2315 style packs.
The platters are not the same thickness between the 7900 and 7906
Click to expand...
I hadn't realized that. I see that 07906-90904_TechInfPkg.pdf on page 1-2 states "HP does not presently manufacture its own media or discs from scratch but does assemble discs into pack or cartridge configurations (figures 1-2 and 1-3)." and then "As shown in figure 1-4, the base material of a disc is a stabilized aluminum blank 14 inches in diameter and 0.050- or 0.075-inch thick." These statements _seem_ to be specific to the 7906 so I have been assuming that the difference relates to the fixed vs. removable platter ... although Figure 1-2 illustrates the construction of a three platter removable pack that's clearly not intended for a 7906.

I haven't been able to locate any technical information specific to the HP 12940A Disc Pack. Maybe it uses a 0.075-inch thick platter for increased robustness?

The HP 7900A (24 sectors) takes an HP 12869A Disc Pack. Specific technical information also missing, however 07900-90022_7900A_Service_Training_Manual_Jan72 on page 1-3 (7900-39) shows the same generic illustration of "storage media" stating a platter thickness of 0.050". Page 1-5 specifically states "0.050-inch-thick". The illustration on page 1-4 (7900-41) shows a breakdown of a cartridge in which there appears to be a notched ring present ... although eyeball-estimate of the notch count seems to be only 8 or 10. Fortunately page 2-3 states:

"Attached to the bottom of each disc is a short, thin-walled skirt with slots cut in it. This slotted skirt,
together with a photocell assembly for detecting the slots, are used for detecting disc rotational disc
position. If radial lines were drawn through the slots, the disc would be divided into 24 equal pie-shaped
segments."

It seems like the HP 12869A Disc Pack for the 7900A is conventionally constructed for 24 sectors.

The HP 12940A Disc Pack for the 7906A is the unconventional one, both as regards the lack of a sectoring ring and based on @Al Kossow observations and the notes above it's of unusual thickness guaranteed to crash the heads on other drives ...
 
pbirkel@gmail.com said:
The HP 12940A Disc Pack for the 7906A is the unconventional one, both as regards the lack of a sectoring ring and based on @Al Kossow observations and the notes above it's of unusual thickness guaranteed to crash the heads on other drives ...
Click to expand...
It appears that one could potentially fit a HP 12940A Disc Pack into a variety of drives given the missing ring and then attempt to load the heads (to their detriment), but not the other way around where the ring would likely protrude into something. Hopefully there are other mechanical differences in the spindle surfaces to would preclude such a mating ...
 
The only reason I bring this up is that pack with just an index slot in a DEC RK05 shell would be a disaster if the platter is too thick.
Why would someone do that?
 
Al Kossow said:
HP 7900A is 24 sector
Burroughs B1700 is 32 sector
Click to expand...

I see that Diablo series 30 outputs the 5th sector address bit on pin UU...

View attachment 1282552

...but the RK05 edge connector interface doesn't have a pin allocated for this signal. It would be possible to choose an unused pin on the edge connectors to support the 5th bit.

I imagine the greater need is to have a disk tester read B1700 disks and not so much to emulate a drive with 32-sector disks to boot up a B1700 computer. Is that what's anticipated?

The reason for asking this question:
The RK05 Emulator/Tester has 20 input signals and 20 output signals.
If an additional Sector Address bit is needed, then it would be an Emulator output and a Tester input.
There are currently 4 spare bus receivers on the Emulator/Tester PCB with inputs grounded and outputs not connected. One of those could be used to receive the 5th Sector Address bit.
There are no spare outputs in the design, so if it were necessary to emulate a 32-sector drive then an additional driver IC would be needed.

I'm thinking the following might be possible:
Decide which unused RK05 bus pin might be appropriate to assign to be the 5th address bit.
Assign a 5th address bit on the dual 40-pin cable.
See if it's possible to route traces on the Emulator/Tester PCB from this RK05 bus pin to a spare receiver input, and from the spare receiver output to an unassigned/spare FPGA pin.
The Tester Adapter paddle card (accessory "A6") needs this 5th sector address bit, or maybe a blue wire could be added for those who need it.
The dual 40-pin to Diablo/Winchester MRAC42S adapter also needs a trace or jumper for the 5th Sector Address bit.

No need to modify the M993GW paddle card (accessory "A4") because Emulators would not support the 5th Sector Address bit. Only Testers would use it.

Tester FPGA firmware and RPi Pico software needs to be updated to support 5 bits instead of 4. No change to Emulator FPGA firmware and RPi Pico software.

If this is only a Tester capability and not an Emulator capability then it seems possible. This is the time to support it before ordering the next larger round of PCBs.

Does anyone need to emulate a drive with more than 16 sectors? HP systems, maybe?
 
gwiley said:
I imagine the greater need is to have a disk tester read B1700 disks and not so much to emulate a drive with 32-sector disks to boot up a B1700 computer. Is that what's anticipated?
Click to expand...
Correct. CHM has packs I'd like to try to recover the software from, but no machine
I suspect we may be the only place in the world that still has any
 
gwiley said:
Does anyone need to emulate a drive with more than 16 sectors? HP systems, maybe?
Click to expand...
That would be at least me; undoubtedly others who don't visit this forum. HP 2100 and 21MX controllers (a two board set) for the HP 7900A (a removable cartridge plus fixed disk on a single spindle; 24 hard-sectored) remain modestly common, whereas the 7900A drives do not - the typical scenario for equipment of that era. The problem with the 7900A and then the 7906A is the unique drive mechanism; it's not simply a repackaged Diablo drive or similar (e.g., RK05) with a single cartridge. It would of course be fine to simply emulate either half (or both halves) of the spindle (the removable or the fixed subsystem). After these two drive families HP consolidated all (?) of their high-speed interfaces into the HP-IB specification by which point AFAIK Diablo-era drives were supplanted by flexible disks on the low end and Winchester-era drives on the high end. @Al Kossow can probably describe this transition better than I.

IMO the high-value target would be emulation of the HP 7900A (24 hard-sectored). Emulation of the HP 7905A or 7906A (24 soft-sectored) would I suspect be a bit less valuable in general as the required HP 13037A controller is a completely separate 3U chassis that typically appears/disappears with the drive itself, the remaining in-computer interface being little more than line drivers/receivers to the external chassis. The HP 13037A controller also supported the later higher capacity HP 7920 and 7925 which were more traditional multi-platter removable pack drives. The three platter 7920 has 48-sector servo information on the last platter surface; the five platter 7925 has 64-sector servo information on its last platter surface.

I'm not sufficiently familiar with the HP 7900A controller, the HP 13210 Disc Interface, to judge whether your emulator could be successfully fit to it (assuming that it could handle the 24 sector requirement). However there is a pretty good HP guide to interfacing the 7900A that I've attached here that will answer your questions in that regard much better than I. AFAIK there is no comparable interfacing document for the HP 7905A/7906A and I've not yet figured out a good substitute.

There are good archives of software for HP 2100/21MX era systems; generally folks fit the later HP-IB interfaced drives to them due to significantly greater drive availability plus there are emulators that support the HP-IB interface: https://www.hp9845.net/9845/projects/hpdrive/#hpdrive It would still be really nice to be able to fit the earlier drives to existing controllers through emulation, regarding which IMO the HP 7900A is a worthy target
 

Attachments

gwiley said:
Does anyone need to emulate a drive with more than 16 sectors? HP systems, maybe?
Click to expand...
There are also Data General Nova/Eclipse-era systems that might be considered. I believe that I discussed those on another of your threads but can't find that message at the moment. The good news here is that DG interfaced Diablo Series 30 drives as their 4047/4049 subsystems which used "adapters" to DG Model 31 and 33 disk drives (which I believe were simply the corresponding rebranded Diable drives), respectively. These both appear to have been 12 hard-sectored.

I don't have the required DG 4046 controller or either adapter, none of which have available documentation, so I can't say much more than that. But if you have 12-sector format covered already for PDP-11 RK05 systems and expect that Diablo Models 31/33 are supported (through innovative cable connector techniques!) then it seems to me that your emulator would be in a good position to support some of the early DG systems.
 
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