[Coco] How much memory

Wayne Campbell asa.rand at gmail.com
Sun Nov 28 14:36:48 EST 2010

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.


----- Original Message ----- 
From: "RJLCyberPunk" <cyberpunk at prtc.net>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Saturday, November 27, 2010 8:52 PM
Subject: Re: [Coco] How much memory

>I find it odd that OS9 has that limitation that all other current computer 
>operating systems do not have. why have the designers of OS9 built a 2MB 
>memory address limitation?
> ----- Original Message ----- 
> From: "Robert Gault" <robert.gault at att.net>
> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
> Sent: Saturday, November 27, 2010 8:23 PM
> Subject: Re: [Coco] How much memory
>> Frank Swygert wrote:
>>> One little nit though -- BASIC can't address 512K, not without a
>>> lot of modification anyway. BASIC is still limited to 64K without bank
>>> shifting some of the RAM or using some other tricks.
>> I have to take issue with this statement, Frank. :)
>> Super Extended Basic on the Coco3 can and does use more than 64K whenever 
>> you use the high res text or graphics screens. There are quite a few 
>> programs that combine Basic and ml programs to use the full 512K memory.
>> As already stated by others, OS-9 can easily use 2Megs of memory but 
>> unfortunately the operating system itself can't use more than 2Megs.
>> Keep in mind the boards by Paul Barton that had 8-16Megs of memory. So 
>> any new "Coco" should have at least 2Megs.
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