While chatting about data recovery, an obscure filesystem came up. It apparently claimed the MBR partition ID 0x20 and was named "Willowsoft Overture File System (OFS1)". In the modern world, it seems to only be seen when a partition table is corrupted.

Digging back a bit, it's possible to find references to it going back to 2000: https://web.archive.org/web/20000903024208/https://www.win.tue.nl/~aeb/partitions/partition_types-1.html


Rumoured to be used by Willowsoft Overture File System (OFS1), if there is such a thing.

With a possible relation to a "Willowtech Photon coS":


Used for Willowtech Photon coS (completely optimized system) by [email protected]. See dejanews.

A bit more digging and the earliest reference I can find is from 1997: https://groups.google.com/forum/#!search/willowsoft$20overture|sort:relevance/de.comp.standards/upmxnfn2DAs/yXlOFDvXD84J

Unfortunately, this is where the trail gets cold. dezine.net appears to have been a web hosting company. Dejanews was apparently acquired by Google, and not much more is available on Google Groups.

I would like to know where this filesystem was used - was it on an IBM PC-compatible, as the use of MBR suggests? Was it older, or contemporary with PC-DOS/MS-DOS? Did it even exist?

  • 7
    "Dejanews was apparently acquired by Google"? Is that considered an obscure bit of ancient history now? Yes, they famously acquired it (causing Google Groups to be referred to by the nickname DejaGoo for a while) and ruined its searchability (while vastly increasing the number of users spewing low quality posts toward Usenet), explaining why you probably won't find the reference that someone expected to direct you to by saying "see dejanews"
    – user5152
    Commented Feb 2, 2018 at 2:04
  • Some documents refer to it as having been reserved by Willow Schlanger, whoever that is, so it sounds like it might just be a hobby OS developer who once had a hand in compiling a reference document that out-survived its peers? Never forget to allow for the very limited routes of data propagation in the old days. And no real company would ever claim they had a 'completely optimised system' with a straight face, surely?
    – Tommy
    Commented Feb 2, 2018 at 2:38
  • 1
    @Tommy - there's a Stack Overflow user of that name whose home page setting is a link to a google code archive of a project including red-black tree implementations in C++. His personal homepage suggests he is indeed involved in hobbyist OS development, so is likely the originator of the system mentioned.
    – Jules
    Commented Feb 2, 2018 at 14:12
  • Andries E. Brouwer’s list of partition types is still active; I’m guessing the entries there are based on lists compiled by Andries or Matthias Paul (who added the Wikipedia entry in January 2012). The entries also made their appearance in Ralf Brown’s Interrupt List version 55 or 56 (December 1997), but the changelog doesn’t mention them so that won’t tell us where the information came from. Commented Feb 2, 2018 at 14:48
  • Actually Willow Schlanger appears in the RBIL contributor list, so the information might have come directly from him... Commented Feb 2, 2018 at 14:52

1 Answer 1


Documents such as this expand slightly on the attribution of 19h to Willowtech Photon COS with:

Code 19H is Claimed for Willowtech Photon COS by Willow Schlanger.

So Willowtech was either an individual or a company named after its founder.

Willow Schlanger is named as a contributor to Ralf Brown's Interrupt List in 1997, which is the oldest source that has yet been discovered for this partition documentation.

A Willow Schlanger maintains a copy of that document on his personal web page and also offers other relatively low-level documentation. His blog reveals that he was born in 1982, so was the correct age to be making hubristic statements about "completely optimised system"s in 1997. Willowtech remains entirely obscure.

So the likely sequence of events is:

  • a teenager, interested in OS development, helped to compile BIOS documentation that includes a list of master boot record IDs;
  • being interested in hobby OS development, he decided to reserve an ID for his own use;
  • the document he contributed to happened to become the only readily-available source for those numbers; and
  • as such his product-that-probably-never-was has found itself included into a whole bunch of other, more prolific documents.

Most of us are lucky enough that our teenage actions rest safely in the past. One of Willow Schlanger's happens quietly to have gone viral.


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