[ltp] Memory Module Question 2

[Eric Jorgensen]

On Fri, 5 Jul 2002 18:29:52 -0400
"Shingo Tamaru" <stamaru@andrew.cmu.edu> wrote:

> Luca.
> I recently encountered this info.
> 
> In order for TP600 to recognize full memory size,
> one of the two memory slots needs to have PC66 module.
> If a PC100 module is installed into the slot which
> can take only PC66, the half bank of the memory module
> is disabled.


	That's, ah, not entirely accurate. 

	I'm not disagreeing with you, I'm sure that you had a situation where a pc66
module worked and a pc100 module didn't, but that's not the way it works. 

	I did a lot of research on this once, and it turns out that the differences
between pc66, pc100, and pc133 are all electrical differences, and have very
little (nothing, in the case of pc100 and pc133) to do with speed. I have some
pc66 dimms that are 6ns and I have some pc133 dimms that are 8ns. 

	The major differences have to do with minute differences in the electrical
tolerances with regard to the resistance and capacitance on the lines that
connect to the row & collumn drivers in the memory chips themselves. 

	This is the same reason why there are some EDO simms that will work in any
pentium board except those with an internal clock speed of over 166mhz, even
though the external clock is always 60 or 66mhz. I actually have a simm that
works fine at 166mhz but has about 4k of bad bits in a 200mhz box. it's all
about row & collumn drivers being able to put up with the access rate, which has
very little to do with the refresh rate or the speed of the interface. (well,
some, but, mostly it has to do with how fast the processor can actually do it
through your chipset). 

> I found that one guy successfully installed even
> 32MB onboard + 128MB PC66 + 256MB PC100 = 416MB total
> on TP600.
> 
> http://zurich.ai.mit.edu/hypermail/thinkpad/2002-05/0397.html


	Chances are, the older ram is a more primitive configuration - this is the same
reason that some dimms are sold as "low density", because a 440bx chipset can't
handle a 128x32 chip configuration, but it can handle a 64x64 chip
configuration. The chipset just doesn't know how. 

	The 228 meg thing is probably due to a scarcity of address lines on the board -
I'd be glad the configuration worked at all with some missing megs vs. not
working period. 


 - Eric



> ----- Original Message ----- 
> From: "Luca Benelli" <luca.benelli@libero.it>
> To: <linux-thinkpad@www.bm-soft.com>
> Sent: Friday, June 28, 2002 9:17 AM
> Subject: [ltp] Memory Module Question 2
> 
> 
> > Hi everybody,
> > Talking about memory...
> > does anybody know why my TP600 uses less than the available memory?
> > The TP600 should be able to use up to 256 MB of RAM... 32 are onboard and I
> > added 2*128Mb that should add up to 288... but when i boot the system only
> > 228 are usable (the bios sees the complete amount but it says that only 228
> > are usable)...
> > 
> > Thanks in advance, Luca
> > 
> > 
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> > 
> 
> 
> 
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