Re: BASIC OS for the PC

Hello!

Baltissen, GJPAA (Ruud) wrote:

> So far I developed my own file system (FS), but one based on Commodore's
> one with BAM and linking bytes in every disk sector. I added my own
> things like a time stamp and not using two bytes as link but four to
> overcome the 16 MB limit of Commodore's two-bytes link system.

Two things which are quite annoying in that kind of filesystem:

* The sectors not hold odd number of bytes - in case of Commodore, 254
instead of 256.

* It is difficult to implement file seek operation - you need to read
every sector in a file up to the desired location to seek (unless you
implement more sophisticated moechanisms like REL files).

For these reasons, I think FAT is much better filesystem.

> All my old IBM PC/XTs have at least 256 KB of RAM so I decided not to
> limit myself to 64 KB (or less) as the C64 does but to use the RAM more
> in the way the C128 or a CBM-II does: 64 KB for the program and 64 KB
> for the data. The next step in the future is evident: using more than 64
> KB for both parts of course. The length of variables won't be limited to
> just two characters and I think 16 chars is reasonable.

You can do the same as the CBM-II 256: first 64 kB bank for the program,
second for string variables, third for numeric variables, and fourth for
arrays.

> Commodore stores variables in programs by storing the complete name.
> Another idea I have is to replace the name by three bytes: one token and
> two bytes. These two bytes point directly to the data. 

And what happens when a variable gets deleted? Is there a garbage
collection in the variable area? If yes, then the addresses of the
variables after the deleted one will be changed. You will then need to
change these addresses in the program code as well. Looks complicated.

> I also have been playing with my own DOS. The look and feel should be
> like MSDOS so I won't alienate people right from the start. But other
> things will be completely different. I assume that you are all familiar
> with the DOS commands DIR, TIME and DATE. In MSDOS these commands are
> incorporated in COMMAND.COM. In my case they are separate programs like
> DEBUG and CHKDSK. 

Well then, don't forget things like DEL, REN, TYPE and so on - they are
quite useful too ;-)

Regards,
Michau.

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