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Tandy 5 Meg Hard Disk

I

IBM Portable PC

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Jan 15, 2008
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70 Miles NW of Melbourne, Australia
I just unearthed my Tandy 5 Meg drive, which I purchased a couple of years ago on ebay. Amazingly both the exterior and interior are immaculate, it was clearly hardly used. I also managed to buy some pure unobtanium a few months before that, an original Tandy hard drive Model 1 bus to 50 pin drive adapter.

My plan Is to replace the actual drive with an MFM emulator, https://www.pdp8online.com/mfm/mfm.shtml, has anyone tried this combination yet?

Also, from what I understand currently, Tandy designed the first controller board in-house, before using off-the-shelf WD controllers in their 8 Meg and later drives. Can anyone confirm that this is the case?
 
Wasn't the 5 meg model an SA1000? Interface is a bit different, as is the data rate. I suppose that David's emulator will work, but since the drive used the WD1001 controller, wouldn't it be easier just to address the host-to-controller interface?

The interface is very simple; when I put an SA1002 drive with WD1001 controller as the first hard drive on my 5150, the ISA interface was just a couple of ICs; mostly address decoding and transceivers.
 
Chuck(G) said:
…Since the drive used the WD1001 controller,
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I don’t believe the controller is a WD1001. There are no WD markings while the 8X300 controller chip is in the center of the board, and not in one corner as depicted in the WD OEM manual.

As mentioned, I have the original host (Model 1 EI 40 pin to WD interface [It appears that Tandy copied the WD1001 host pinout]) to controller interface, which does indeed only have a couple of components for address decoding.
 
I believe that all of the 8x300/305 HD controllers are based on a single reference design. I've got one vendor-specific model here for an ST412-interface disk. Because I don't recall anyone writing ROM code for the 8x300, I suspect that the controller firmware could be had from third-party sources.
 

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IBM Portable PC said:
My plan Is to replace the actual drive with an MFM emulator, https://www.pdp8online.com/mfm/mfm.shtml, has anyone tried this combination yet?

Also, from what I understand currently, Tandy designed the first controller board in-house, before using off-the-shelf WD controllers in their 8 Meg and later drives. Can anyone confirm that this is the case?
Click to expand...
I am running with the Gesswein MFM emulator in one of my 5-Meg Tandy drives. Works just fine. On the second point, it was actually WD who designed the 8x300 based solution as a stop-gap pending release of the VLSI controller chip.
 
Even the 8x30x controller was a big advance--you could fit a hard disk controller on an S100-sized card. I have an older SA4004 disk unit whose controller matches the footprint of the drive--and the SA4000 is a 14" drive. Lots of SSI TTL. MOS/CMOS hadn't yet gotten the kind of speed needed.
 
shirsch said:
it was actually WD who designed the 8x300 based solution as a stop-gap pending release of the VLSI controller chip.
Click to expand...
What was the ID of the subsequent VLSI chip?

Do we know what the last firmware version was on the Tandy designed HDC?

Is there a name for the 50 pin interface on these HDCs i.e. like Shugart Associates interface for FDDs?

Was there ever a third party adapter to connect these drives to a CoCo, and drivers for any DECB derived DOS, or Microware's OS-9?
 
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I don't think it was a single chip, but rather a set. There's a WD Data Products databook for 1984 on bitsavers; call me lazy to not grab my copy and answer your question about the chip.
As far as the SA4000/SA1000 interface; it's basically the same as the ST506, right down to the differential data lines, just in a 50 pin control connector rather than a 34 pin one for all intents and purposes. Much like the SA800 8" floppy connector vs. the SA400 5.25" one. Data rates are a bit different (5 MHz vs. 4.2MHz).
The hard disk interface basically added a differential signal cable to the floppy interface.
 
I don't know about Tandy's 8 and 15 MEG external HDDs, however, the 5 Meg HDD's power key switch keys have a 6 digit code stamped onto them e.g. my units keys contain 01112B. The only other writing is "MADE IN U.S.A.".

Having duplicates made is cheap enough, although originals are often more reliable and work more smoothly. Does anyone know if these key switches, or keys, were custom made for Tandy, or are they an off-the-shelf item?

If the latter, some coded key ranges can be ordered online simply by quoting the code e.g. some filing cabinet keys e.g. from Keys by Code, Code Cut and Precut Mr Lock, Inc. (I have now emailed Mr Lock with some details, after finding a similar looking key on their site)
 
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Chuck(G) said:
As far as the SA4000/SA1000 interface; it's basically the same as the ST506,
Click to expand...
They are similar but SA4000 has on drive data separator and uses data clock signals so SA1000 and SA4000 aren't interchangeable. I would consider the SA4000 closer to ESDI than ST506.

Did anybody make a controller that supported both SA4000 and SA1000?
 
The SA1000 series came out in 1979. The ST-506 came out in 1980, the ST-412 in '81. Comparable capacities, smaller form factor, higher performance.
 
eswan said:
The SA1000 series came out in 1979. The ST-506 came out in 1980, the ST-412 in '81. Comparable capacities, smaller form factor, higher performance.
Click to expand...
Plus the ISA bus wasn't a thing until 1982. By the time any vendor was able to ship a fixed disk controller for the 5150 there was considerably better options.
 
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