[Coco] General Memory Question about speed

[Gene Heskett]

On Sunday 13 January 2008, Dave R in Illinois wrote:
>I meant to say 100ns. Or would 150ns be pushing it?

I *think* I have some 120ns stuff in my 2nd coco3 with a half meg board in it.  
The 2 megs kit in the main one is 90ns I think.  Those both work ok and the 
90ns stuff runs dead cold at the actual clock speed it is being run at.  I 
can toss a furniture blanket over it with a photo thermometer under it, and 
the temp rise after several hours is 2 degrees.  It also has a 63C09 in it 
and is running on an old AT power supply wired externally.  But it isn't the 
memory speed that controls the coco's speeds, its the 'dot' clock speed being 
tied to the display standard where the machine was intended to be used.  That 
is in the general area of 14.3 mhz, and is further divided by either (IIRC) 8 
for the 3's, and 16 for the originals and 2's to get the actual cpu clock of 
(for NTSC, PAL is slightly different) 0.889 mhz for the 1's and 2's, and 1.79 
mhz for the 3's.

A side comment here, applicable to the 63C09 equipt machines.  The cpu is not 
the limiting factor for speed, the gime is.  Its output drivers are so puny 
they simply cannot drive a memory interface line fast enough to make use of 
faster memory.  What we really, really need, is a replacement gime made with 
modern cmos technology.  And thumb our nose at the FCC who mandated the noise 
abatement design that made it so in the first place, combined with Tandy's 
refusal to apply a shielding scheme that might have actually worked.  But I 
digress...

>Dave
>
>On Saturday 12 January 2008, Lazy wrote:
>>Would upgrading the memory in a Coco 2 from 20ns to 10ns provide a
>>
>>noticeable difference in speed?
>
>Since memory speed of the original was about 250ns, and the cycle itself is
>much longer than that, no. And it may lead to troubles using memory that
>fast in a circuit designed for 10x slower speeds as the faster memory may
>suffer from noise glitches the slower stuff ignores.
>
>
>
>
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-- 
Cheers, Gene
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