[Coco] How much memory

Aaron Wolfe aawolfe at gmail.com
Sun Nov 28 21:19:43 EST 2010

On Sun, Nov 28, 2010 at 2:36 PM, Wayne Campbell <asa.rand at gmail.com> wrote:
> Just to throw out a couple of things I thought about. I remember wondering
> why we were stuck with a 64K barrier when DOS (running on a 8-bit 8086/8088)
> was able to access 640K of continuous RAM. That's 10 times as much. I know
> DOS used tricks to achieve it, but the computers were not slowed down by
> these "tricks" at all. Nor were they slowed down when Extended and Enhanced
> memory were introduced. Is there a reason DECB/SECB and/or OS-9 could not be
> made to do that?
> As for OS-9, as I recall, the memory was allocated in 64K chunks per window
> (on CoCo3), all one chunk on a CoCo2 (I never had a CoCo1, so I don't know
> if it was ever expanded to 64K). The "system page" in OS-9 used 1 64K chunk,
> and when the system was loaded you had ~32Kof available space in that chunk
> for loading more modules. Each hardware window is allocated a 64K chunk.
> After the system modules for that space are loaded, you have about 40K of
> space left in that chunk. While this may be plenty for a program written in
> ASM/RMA, it can run out quickly when programming in Basic09, C or Pascal,
> especially when you are writing an application (as opposed to a utility
> program). This is true especially when you are learning to program.
> DCom, as it started out, was larger than 40K total, and I had to break it
> into separate parts that would be loaded "in turn" as each step occurred.
> Having worked on trying to finish it, I discovered that I had written it
> very badly, even if it was "everything I knew about programming". However,
> this does not mean that the program would be necessarily small enough to run
> in 40K of space even in the form of unpack (it's replacement) when it is
> finished. I started running into that wall with unpack and with decode (the
> test program) as well. I learned that I needed to sacrifice comment lines if
> I was going to make everything fit, and then my code might not be so
> readable. Replacing cryptic variable names with longer descriptive names
> didn't help either. I sinply used up the extra space with the longer names.
> I always felt like it would be nice to be able to write a program as a 60K
> app, if that's what it took, and then start whittling it down to see how
> small I could make it. Of course, that never happened, and decode and unpack
> are, as yet, unfinished.
> I realize that with the new FPGA-based CoCo4 design, memory will be dealt
> with differently. However, I think OS-9 and DECB/SECB will still have to be
> modified to deal with the extra memory, if any part of the plan includes
> being able to access more than 64K per window.

Hey Wayne, it's been a while, hope things are going well for you.

Have you explored the option of splitting your Basic09 program into
several modules?  Each would have it's own 64k space if I understand
the system correctly.  Your source could be much larger this way too.


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