[Coco] Patching NitrOS9 for 8 meg

[Dave Philipsen]

> On May 3, 2018, at 12:41 PM, RETRO Innovations <go4retro at go4retro.com> wrote:
> 
>> On 5/3/2018 10:20 AM, James Jones wrote:
>> Take a look in Chapter 2 of Kevin Darling's _Inside OS-9 Level II_. (
>> http://wiki.yak.net/1087/InsideOS-9LevelII-KevinDarling_1987_.pdf)
> Looked, but I don't see the concern over moving past 2MB.  Yes, one needs to move to words across the spectrum, but P$DATImg has 64 entries, only 16 of which are used currently.  What am I missing?
> 
> I don't think one needs to know about the state of all 8kB blocks in RAM, just the 8kB blocks currently mapped by a process.
> 

‘One’ doesn’t need to know.  But the system may need to know.  When a new process is created, how does it know which blocks of memory to claim as its own?  With 8 MB of memory there are 1,024 blocks to choose from. If the first process that starts takes blocks 1,2,3,4, as its own, then how does the second process know to take blocks 5,6,7,8?  If, while a process is running, it decides to ask the operating system for more memory (which is possible with OS9) then how does the operating system know which blocks to give it?

I may be wrong but as I see it the operating system must know the status of all memory blocks and which ones have been allocated to processes and which have not.


Dave

> (Yes, one needs a FREE/BUSY map of all blocks, but one only needs 1 bit per 8kB block, so only 32 bytes for 2MB, 64 for 4MB, 128 for 8MB, and 16MB only needs a page of 256 bytes.)
> 
> Jim
> 
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