SWTPC 6800 - SDOS Operating System

Demonstration of the SDOS operating system running on a SWTPC 6800 computer.
Link to Roberto's GitHub repository that includes several 6800 operating systems he has running on his for of the SIMH emulator: github.com/rsa...

[@idbaxter]

Hi. SDOS Author here. Its great to see my OS running again after 40 years!

[@lollyrae]

I know the Software Designs founder, Ira Baxter. He's now running a business called Semantic Designs.... with the same SD logo as the original company. They're a software analysis tools company. Here's a comment I got from Ira about this video: Its great to see my OS running again after 40 years! SDOS was designed for fast performance for commercial applications on large disks (e.g., 10Mb), including indexed file; mostly this mean fast access to random locations in a big file. The SDOS design guaranteed at most 2 disk seek/read steps to get to any random file data: one read of a file header block, one read of the selected data block; In contrast, the linked sector OSes all had to riffle through linked sectors to get to random places OUCH!.. With the built in cache, the header block tended to stick around and so multiple random access to the file could be achieved in one seek/read step…. you can’t do better than that with really big files.

[@Desmaad]

The 6800 had a surprising number of operating systems.

[@e_fission]

Thank you for another excellent, informative video. I'm surprised how many operating systems were available. It's neat to see what overlaps between them, and where they differed, too.

[@herdware]

That was a pretty neat OS.

[@yankeebotanist4699]

Hi there!! Do you have a website by chance? Its regarding the telatype videos, do you make and sell the interface for a computer to a telatype? Might be getting one from the 1930's and need a way to interface with it.

[@ninoivanov]

I don’t get this: videos like this, brilliant, in-depth, stylish, educational - 2-3k views; videos of some rando soldering through-hole components - boom, tens of thousands of views. KZbin is really trash in how it rewards videos, essentially favoring online Idiocracy over valuable material.

[@steveblakely7296]

Of all the operating systems you have talked about for the 6800, which ones if any supported directory structures or did that come a lot later in DOS development?

[@idbaxter]

The biggest drive we had with SDOS was 10Mb. A single level directory was adequate to handle several thousand files. Name lookup was by hashing so it typically only took a single seek and sector read. We consider directory hierachies late in SDOS's life but didn't get there. It wasn't exactly a new idea; at least Multics (MIT circa 1967) already had this idea.

[@retrozmachine1189]

I'm guessing it has a few sectors dedicated to the free space bitmap since there isn't a central file space allocation table.

[@deramp5113]

The file DISKMAP.SYS is the used/free space bit map.