[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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