free ram on 16K systems with various DOS?

[scottinNH]

I've heard that DOS won't run on 16KB, but I've also heard that's a small exaggeration (there IS free RAM after DOS and cartridge BASIC load -- but "not much").

 

Surprisingly, I couldn't find precisely how much using a few Google searches.

 

Ignoring "game DOS" loaders (meaning, you can type "DOS" in BASIC and get something), how many bytes free with 16KB?

[Rybags]

It usually will run in 16K Ram but the free space will make you wonder why you bothered.

Half the point of floppy vs tape is that it's a lot faster but the true advantages shine through when dealing with files more than about 4K in size.

 

The top of memory used by a Dos will usually change depending on how many drives are enabled and how many file buffers are in use. A typical configuration is 2 drives and 3 file buffers.

 

Top of free Ram in a 16K system will usually be $3C1F - that's just under where the Graphics 0 Display List starts - note that most bitmap modess will leave less memory free than that and if there's insufficient free Ram you won't be able to use the more memory hungry graphics modes.

 

I've just loaded Dos 2.5 in an emulator, it's a less memory hungry Dos if you ignore the fact that DUP when loaded will need another big chunk. Bottom of free Ram is around $1D80.

That leaves just under 7.5K of free Ram for a Basic program - just under 6K worse off than not having Dos loaded.

 

Later versions of more advanced Doses like SpartaDos would likely not work with 16K. Some Doses including SDX can use parts of extended and high memory for buffers and code which leaves more free in the main area for Basic.

[scottinNH]

>That leaves just under 7.5K of free Ram for a Basic program - just under 6K worse off than not having Dos loaded.

Excellent! Thanks. To me that's quite usable. I've received parts for the 64K upgrade, but now I know I can get the SIO2PC running first (assuming RAM use is in the same ballpark).

~7K free seems PLENTY to write small text-mode code, and interact with joystick and SIO data lines.

[+DrVenkman]

... now I know I can get the SIO2PC running first (assuming RAM use is in the same ballpark).

 

From the Atari’s perspective, the SIO2PC itself is invisible, really. The peripheral emulation software on your computer or RPi (APE, RepesQt, SIO2OSX, whatever ...) is just another disk drive. So free ram will depend entirely on whatever DOS you boot.

[ricortes]

Almost unfond memories of memory. I remember thinking some people used graphics(1) in their programs just to squeeze another 300-400 bytes out of their 16k systems. You can always use a cassette instead of DOS for a few extra bytes! j/k

[+slx]

DOSXL leaves about 6600 bytes free but you don't need space for a DUP as it has a command line interface.

 

With XDOS 2.43N its 7454 free bytes, also with a CLI that seems to have more features than DOS XL.

Edited June 15, 2017 by slx