Portable Wafer Tape Data Storage for TRS-80 Model 100

I was helping a friend clean out a house he just purchased, and ran across this little gem, a PMD-100 made by Holmes Engineering Inc. I know nothing about this drive, and have never run across one before. If anyone has any info on it, I would appreciate it greatly.



Welcome! Nice gadget. There’s a 1984 review here.

It can store up to 10 files, and has to run through the whole tape loop three times to perform a save operation. It has a local buffer of 12k bytes to allow it to do that in the background. But if when reading back it detects a checksum mismatch, you don’t get any bytes at all.

It took about 25 seconds to save a short (750 byte) test file as the first program on a 5-foot wafer and 165 seconds on a 50-foot tape. Saving the same program as the last file on a 5-foot wafer took 30 seconds, and saving it as the tenth file on a 50-foot tape required 250 seconds. In comparison, it takes about a minute to save, rewind and manually verify a similar file on cassette.
The wafer tapes hold about 1K per foot and are available in lengths of 5, 10, 20, 35 and 50 feet. Holmes’ prices are not available, but the wafers typically sell for $3.50 to $4.50 each

Neat! I hope the tapes have fared better than many other proprietary tape products. Many of them are vulnerable to sticky rollers, de-laminating media, or other difficult-to-recover failure modes.

Thanks for all the info! It’s a neat device, I just don’t have the proper hardware to give it a test.

I have about half a dozen tapes that I found with it. I just don’t have a setup to test the functionality.

Sinclair went in for the MicroDrive, a similar technology with a 5m tape in a “wafer” pulled past a conventional head. The tapes tended to stretch with use, so you get more storage(!) but you will need to resave your data before it becomes so stretched it’s unreadable. Apparently about 90kbytes of capacity.

The weak spot with using old wafers is the foam pad which provides pressure to the back side of the tape - readily replaced.