4Mb SIMMs in a 4D/25TG: Chips from some manufacturers don't work!

[Chris Miller]

Problem:	Chips from some manufacturers don't work!

There have been a few postings regarding using 4Mb SIMMs in a personal IRIS.
Here is a summary of our experiences.

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The SIMMs were purchased from Clearpoint, only current GSA schedule vendor,
at a GSA price of $360/module.  Half of the SIMMs are marked as (pardon the
crude graphics):

	module ID tags:			chip numbers:

 --------------		 ---------	TOSHIBA
| TOSHIBA      |	| 9025AAA |	TC514100J-80 
| THM94000S-80 |	| JAPAN   |	JAPAN 9020HDK  
 --------------		 ---------


and the other half (Hitachi) have no module IDs, only chip numbers:

					JAPAN R200
					9026 2NN
					HM514100JP8H

We exchanged these for more Toshiba modules:

 --------------		 ---------	TOSHIBA
| TOSHIBA      |	| 9018AAA |	TC514100J-80 
| THM94000S-80 |	| JAPAN   |	JAPAN 9016HDK  
 --------------		 ---------


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In the descriptions below, 0 = empty slot, 1 = 1Mb SIMM, 2 = 2Mb SIMM, 
H = 4Mb Hitachi SIMM, T = 4Mb Toshiba SIMM.

SGI supports 2Mb SIMMs.  If you use them the installation is:

	2211	2211		For 24Mb. Note: you MUST(!) install
	2211	2211		the 1Mb SIMMs behind the 2Mb SIMMs.

For 32Mb of total memory, the installation pattern is:

	2222	2222		For 32Mb.
	2222	2222


The memory configurations that we have tried are:

	1100	1100		Came up as 8Mb (correct)
	1100	1100

	1111	1111		Came up as 16Mb (correct)
	1111	1111

	TT11	TT11		Came up as 64Mb (wrong)
	TT11	TT11

	T000	T000		Came up as 16Mb (correct)
	T000	T000

	TT00	TT00		Came up as 32Mb (correct)
	TT00	TT00

	HH00	HH00		Came up as  0Mb (wrong!!)
	HH00	HH00

	TH00	TH00		Came up as 32Mb (correct)
	TH00	TH00

	TTH0	TTH0		Came up as 48Mb (correct)
	TTH0	TTH0

	TTHH	TTHH		Came up as 64Mb (correct)
	TTHH	TTHH

	11TT	11TT		Comes up as 16Mb
	11TT	11TT

It appears as though the machine checks the first bank of chips (port 0) to
determine the chip size and assumes that the rest are the same.  The Hitachi
4Mb SIMMs are NOT correctly detected.   

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Our thanks to Clearpoint Research for being gratious enough to exchange the
Hitachi SIMM modules for Toshiba modules (overnight!).