[Coco] Re: Coco Repack

[Mark Marlette]

At 04:38 PM 8/8/2004 -0400, you wrote:

James,

All well and good but how does that suggest any answer to my original 
question? I had no mention of cost, number of transistors, etc, but the 
location of the MMU's additional register space in the I/O map. ???

Still curious......

Mark




>Mark
>
>My best guess as to why there never was 2Meg support for the
>GIME chip came down to cost. To expand the chip to handle the
>extra two address lines is really nothing. An sram memory cell is 6
>transistors times 2 times 16, or 192 transistors. Not a problem
>considering that there already is about 50,000 to 100,000 transistors
>on the die itslef.
>
>The real cost driver would be that to get the extra 2 address lines
>would meand the Z-Bus would have to be expanded two bits to Z10.
>Having already maxed out to 68 pins, another two pins would force
>the chip into a 84 pin PLCC part or an 80 pin PQFP. That would at
>least add another dollar to the product cost and that must  have
>been foun unacceptable even though OS9 could handle 2 Megs of
>memory right out of the box.
>
>just my thoughts
>
>
>james
>
>On 8 Aug 2004 at 12:49, Mark Marlette wrote:
>
>Date sent:              Sun, 08 Aug 2004 12:49:16 -0500
>To:                     CoCoList for Color Computer Enthusiasts
><coco at maltedmedia.com>
>From:                   Mark Marlette <mmarlett at isd.net>
>Subject:                Re: [Coco] Re: Coco Repack
>Send reply to:          CoCoList for Color Computer Enthusiasts
><coco at maltedmedia.com>
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>
> > At 10:24 AM 8/8/2004 -0700, you wrote:
> >
> > Kevin,
> >
> > Since the MMU will have to grow to x8 in size to handle this and have
> > the same total RAM size as the current CoCo3, tre. Where do recommend
> > it be place in the I/O map. Also remember  there are two MMU task
> > register.
> >
> > Mark
> > Cloud-9
> >
> > >Hi,
> > >
> > >         I'm not talking on a per process basis, but a per system
> > >basis. For example, maybe the quatro will use 1k.
> > >
> > >                                   kevin
> > >
> > >jdaggett at gate.net wrote:
> > > >
> > > > Kevin
> > > >
> > > > There can be a danger in allowing dynamic size on the fly.  Two or
> > > > more processes with differing page size requirements are sure to
> > > > have memory over write issues.
> > > >
> > > > james
> > > >
> > > > On 8 Aug 2004 at 9:51, Kevin Diggs wrote:
> > > >
> > > > Date sent:              Sun, 08 Aug 2004 09:51:14 -0700
> > > > From:                   Kevin Diggs <kevdig at hypersurf.com>
> > > > To:                     CoCoList for Color Computer Enthusiasts
> > > > <coco at maltedmedia.com> Subject:                Re: [Coco] Re: Coco
> > > > Repack Send reply to:          CoCoList for Color Computer
> > > > Enthusiasts <coco at maltedmedia.com>
> > > >         <mailto:coco->
> > > >         request at maltedmedia.com?subject=unsubscribe>
> > > >         <mailto:coco-> request at maltedmedia.com?subject=subscribe>
> > > >
> > > > > Hi,
> > > > >
> > > > >  I get it. The segment (block, page, whatever you want to call
> > > > >  them)
> > > > > count is fixed at 256 (i.e. 8-bit). We can change that to if we
> > > > > wanna.
> > > > >
> > > > >  And yes I do realize that NitrOS9 would have to be ...
> > > > >  reworked.
> > > > > Maybe it should be parameterized to handle differing MMU page
> > > > > sizes anyway.
> > > > >
> > > > >      kevin
> > > > > KnudsenMJ at aol.com wrote:
> > > > > >
> > > > > > In a message dated 8/7/04 10:09:18 PM Eastern Daylight Time,
> > > > > > kevdig at hypersurf.com writes:
> > > > > >
> > > > > > >   Forgive my stupidity, but why does reallocating the bits
> > > > > > >   in the
> > > > > > >  address cut the max memory to 1 Meg (from 2?)?
> > > > > >
> > > > > > Let's assume you restrict the MMU registers to 8 bits, so
> > > > > > process DAT images can be stored in one byte per segment.  8
> > > > > > bits means 256 total RAM segments, no more!
> > > > > >
> > > > > > Currently those are 8K apiece, times 256 = 2 Megs.
> > > > > > Many of us once longer for smaller segments, like 4K, but
> > > > > > times 256 is only 1 Meg total.
> > > > > >
> > > > > > It's a tradeoff between total RAM size and segment sizes.
> > > > > > After a lot of public head bashing against the walls, some
> > > > > > years ago we concluded that Tandy's original design of 8K
> > > > > > wasn't so bad after all.
> > > > > >
> > > > > > Besides, it's what the DEC PDP-11 family used -- the machines
> > > > > > where UNIX was nurtured, if not born.  --Mike K.
> > > > > >
> > > > > > --
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