Industry Standard SIMM Modules:

PIN No.	PIN NAME	PIN No.	PIN NAME	PIN No.	PIN NAME

1	Vcc		11	A4		21	WE-L
2	CAS-L		12	A5		22	Vss
3	Data Bit 1	13	Data Bit 4	23	Data Bit 7
4	A0		14	A6		24	NC
5	A1		15	A7		25	Data Bit 8
6	Data Bit 2	16	Data Bit 5	26	Q9
7	A2		17	A8		27	RAS-L
8	A3		18	A9 *		28	CAS9-L
9	Vss		19	NC		29	D9
10	Data Bit 3	20	Data Bit 6	30	Vcc

* pin 18 is A9 for 1M SIMMs and NC for 256K SIMMs


IBM PS2 Model 30/286 -  System Board RAM Module Connector Pin Assignments

Pin	I/O	Signal			Pin	I/O	Signal

1	N/A	+5V (Vcc)		2	I	-Column Address Strobe
3	I/O	Data Bit  1		4	I	A0
5	I	A1			6	I/O	Data Bit  2
7	I	A2			8	I	A3
9	N/A	Ground (Vss)		10	I/O	Data Bit  3
11	I	A4			12	I	A5
13	I/O	Data Bit  4		14	I	A6
15	I	A7			16	I/O	Data Bit  5
17	I	A8			18	I	A9
19	N/A	No Connection		20	I/O	Data Bit  6
21	I	-Write   Strobe		22	N/A	Ground (Vss)
23	I/O	Data Bit  7		24	0	Presence Detect 1 = Gnd
25	I/O	Data Bit  8		26	0	Presence Detect 2 = Gnd or Open *
27	I	-Row Address Strobe	28	N/A	No Connection
29	I/O	Data Bit 9 (Parity)	30	N/A	+ 5V (Vcc)

* Note:  Pin 26 is Gnd if a 1Mx9 memory module is installed and Open 
         if a 256Kx9 memory  module is installed.

(Since the model 30/286 can't use 4 megabyte SIMMs, they aren't considered here.)

Conversion Steps:

To make standard 1M SIMMs work in an IBM, the following conversions 
must be made:

1.	Ground Pin 24
2.	Disconnect Pin 26 from Q9
3.	Ground Pin 26
4.	Connect  Q9 to pin 29
5.	Disconnect Pin 28 from CAS9
6.	Connect CAS9 signal to pin 2

If this sounds like it would be hard to do on a small, surface 
mounted SIMM module, you're right! Fortunately, the SIMMs I've 
looked at have little jumper pads on the back that can be cut with 
an Xacto knife and bridged with a soldering iron. The pads are 
located in the circuit in exactly the right configuration to make 
these changes. If your SIMMs have the jumpers, and you are 
comfortable with performing those modifications, then you're in 
luck. It will take about five minutes per SIMM. Otherwise, you'll 
have to pay a premium price for "IBM" SIMMs.

Final Note: The layout of the jumper pads on the SIMMs allows for 
the grounding of pin 28. Perhaps it is used for a presence detect 
for 4M SIMMs in IBM machines that can accept them.