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Help me Identify this Disk Cartridge, Please

NF6X

NF6X

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I recently bought this disk cartridge from a scrapper on eBay. It was listed as an RK05 pack, but I'm pretty sure that it isn't. Can anybody help me figure out what drive(s) and system(s) it may go with?

It has the same overall appearance as the DECpacks and their relatives, with one platter inside. However, the hub is different. It has one index notch cut into the edge of the hub, similar to the sector notches on an RL pack. It is missing the skirt that DECpacks have with the sector notches and index notch.

IMG_9117.jpegIMG_9118.jpegIMG_9119.jpeg

There are no markings on the pack other than a serial number label, Scotch tape holding the cover shut, and patent number 4,084,200 (Memorex, 1976) molded into the bottom of the housing. Does anybody recognize this cartridge type?

For comparison, here's a 12-sector DECpack that I have, with a view of the sector/index notch skirt:

IMG_9120.jpegIMG_9121.jpeg

I don't have an RK drive to go with my 12-sector cartridge yet, but I'm working on it. I recently acquired an RK-11D backplane and the four main cards to hopefully add a drive to my PDP-11/34A in the future.
 
Diablo Systems sold drives with what they called "pseudo-sectors" which I believe was their name of soft-sectoring. I have an HP pack that also lacks the sector ring.
 
PSEUDO SECTOR MARKS - Rotational speed of the spindle is servo controlled by counting the number of transitions provided by a crystal oscillator between Index
Marks. This provides an extremely accurate speed control which is independent of line voltage or frequency fluctuations. The pseudo Sector Mark line carries these 2000±1 %
square wave clock pulses to the interface. These pulses may be used to format the disk into the desired number of pseudo sectors.

The equally spaced Sector Marks are normally used by the operating system to format tracks on the disk surface into
sectors and the Index Mark is used to establish the beginn-
ing of a track. There is a special circuit in the disk drive that separates the Index Mark from the Sector Marks,
because as they are supplied by the Sector Mark Trans-
ducer, they are indistinguishable. Pseudo Sector Marks are also available at the interface.
These Pseudo Sector Marks are generated by utilizing alternate pulses of the 100 KHz crystal oscillator. These pulses are used to control the spindle speed, and may also be utilized to generate sector formats.

- https://bitsavers.org/pdf/diablo/disk/model_30/81503-02_Series_30_Disk_Drive_Maintenance_Nov75.pdf
Click to expand...

Not really. The drive separates the pseudo sector marks and exposes it to the main interface so that the controller/operating system handles it. For someone who needs a soft-sectored diablo pack this is what they'd need.
For a system that expects hard-sectoring though, they're useless.
 
NF6X said:
Interesting. I assume that without one of those "pseudo sector" drives, this pack is just a wall-hanger?
Click to expand...
From your photos and what I've gleaned from other sources I suspect that it's an HP 12940A (or equivalent) Disc Pack (https://www.hpmuseum.net/display_item.php?hw=418).
I have one grainy photo of a disassembled pack and it does look like yours.

HP12940A - open.jpg

I've been looking for one (or more) of these disc packs for many years now. Perhaps you would part with yours?

The HP 12940A is used in an HP 7905 or 7906 Disc Drive, which is a single-spindle dual drive with one 10 MB fixed disc and one removable pack of either 5 MB (HP 7905) or 10 MB (HP 7906) capacity. It's 411 cylinders with 48 soft-sectors per track; a servo track is embedded on the lower surface of the fixed disc drive, accessed via a special servo head. See Fig.1-1 in 7906_ServiceManual_07906-90903_292pages_Dec83.pdf 07906-90904_TechInfPkg.pdf contains a detailed Theory of Operation; see Section 2-5.

It's not a "pseudo-sector" drive as defined by the Diablo document (https://bitsavers.org/pdf/diablo/disk/model_30/81503-02_Series_30_Disk_Drive_Maintenance_Nov75.pdf).

NeXT said:
I have an HP pack that also lacks the sector ring.
Click to expand...
Perhaps you would part with your disc pack as well :-}? If it's HP then it ought to be the "real McCoy".

My HP 7906A Disc Drive would appreciate the opportunity to put these Disc Packs to work!
 
pbirkel@gmail.com said:
Perhaps you would part with your disc pack as well :-}? If it's HP then it ought to be the "real McCoy".

My HP 7906A Disc Drive would appreciate the opportunity to put these Disc Packs to work!
Click to expand...
Mine has DEFECTIVE written in blue sharpie across the top of the pack and it's been there so long it's permanently soaked into the plastics. If you want it, okay but you will have to trade me for another pack because I use it as a mechanical-fit dummy pack.
 
pbirkel@gmail.com said:
See https://forum.vcfed.org/index.php?t...r-4-sector-decpack-disks.1248827/post-1394356

The HP 12940A Disc Pack for the 7906A is unconventional, both as regards the lack of a sectoring ring and based on @Al Kossow observations and the notes in my post there its platter is of extra thickness (0.075" vs. 0.050") that is guaranteed to crash the heads on other drives ...
Click to expand...

I had not noticed the different platter thicknesses. Now that I know to look for it, I can see that the former mystery pack has a thicker platter. Thanks for helping me identify it as likely being an unmarked HP 12940A pack.

pbirkel@gmail.com said:
Perhaps you would part with your disc pack as well :-}? If it's HP then it ought to be the "real McCoy".

My HP 7906A Disc Drive would appreciate the opportunity to put these Disc Packs to work!
Click to expand...

I am open to that. Do you have anything interesting to trade?
 
Last edited:
pbirkel@gmail.com said:
See https://forum.vcfed.org/index.php?t...r-4-sector-decpack-disks.1248827/post-1394356

The HP 12940A Disc Pack for the 7906A is unconventional, both as regards the lack of a sectoring ring and based on @Al Kossow observations and the notes in my post there its platter is of extra thickness (0.075" vs. 0.050") that is guaranteed to crash the heads on other drives ...
Click to expand...
I just grabbed my defective pack (which is a 12940A) and this is correct. Platter diameter measures 0.075" on a digital micrometer.
 
NeXT said:
Mine has DEFECTIVE written in blue sharpie across the top of the pack and it's been there so long it's permanently soaked into the plastics. If you want it, okay but you will have to trade me for another pack because I use it as a mechanical-fit dummy pack.
Click to expand...
You stick it in other drives than the HP 7906A? Which, and what aspects of "mechanical fit" are you using it to check? DEFECTIVE doesn't have a good vibe to it ...
NeXT said:
I just grabbed my defective pack (which is a 12940A) and this is correct. Platter diameter measures 0.075" on a digital micrometer.
Click to expand...
Thank you for checking!
 
pbirkel@gmail.com said:
You stick it in other drives than the HP 7906A? Which, and what aspects of "mechanical fit" are you using it to check? DEFECTIVE doesn't have a good vibe to it ...
Click to expand...
A physical pack to load into a Diablo drive to check for correct hub mounting, door opening, plenum seal contact and loaded motor spin-up with the head solenoid disconnected. I got the same for my HP 7925. I can do everything but load the heads or it will immediately crash.
 
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