My board has the following specifications:
|JPS||2x10 (ATX holder type)||connected to ATX power supply|
|JLPT||2x13 (pin 26 off)||parallel port connector|
|JFDD||2x17 (pin 5 off)||floppy connector|
|JHDD1||2x20 (pin 20 off)||primary HDD connector|
|JHDD2||2x20 (pin 20 off)||secondary HDD connector|
|JSCSI_1||2x25||Internal SCSI connector|
|J3D||1x20 (pin 7 key) (option)||3D sound card connector|
|JFAN1||1x4 (holder type)||CPU fan connector|
|JCDROM||1x4 (holder type)||CDROM connector|
|JMIC1||1x3 (holder type)||power connector to PW6600 R00B board|
|JMIC2||1x4 (holder type)||MIC left/right/gnd signals to PW6600 R00B board|
|JHEAD||1x5 (holder type)||EARPHONE left/gnd/right signals to PW6600 R00B board|
|JMIDI||2x8 (pin 16 off)||MIDI/GAME port connector|
|JRST/JPWR/JHDI||1x2 * 3 (JPWR pin 2 off)||reset/power/hdd connector connected to PWLT00G R00A|
|JPUSH2||1x2||2nd power on/off connector connected to PWLT00G R00A|
|JPUSH1||1x2||power on/off connector connected to power switch|
|JPRMOD||2x2||CPU operation mode setting|
|603e||1-3 / 2-2||NO_DRTRY|
|604e||1-3 / 2-4||NO_DRTRY|
|604||1-1 / 2-4||FAST_L2|
|604||1-1 / 2-2||Normal||(default)|
|JA2V||2x3||CPU 2nd voltage selection|
|JTAG and JLPD||2x3 and 2x4||2nd cache size setting|
|1-2 / 3-4 / 5-6 / 7-8|
|256PB||OUT / IN / OUT / OUT||1-1 / 2-2 / 5-5|
|256+256PB||IN / OUT / OUT / IN||1-3 / 2-4 / 5-5|
|512PB||IN / OUT / OUT / OUT||1-2 / 3-4 / 5-5||(default)|
|512+512PB||IN / IN / IN / IN||1-2 / 3-5 / 4-6|
|JCLK||2x3||CPU bus clock setting|
|Bus/PCI||1-2 / 3-4 / 5-6|
|50 / 25||IN / IN / OUT|
|55 / 27.5||OUT / OUT / OUT|
|60 / 30||OUT / IN / OUT|
|66 / 33||IN / OUT / OUT||(default)|
|75 / 37.5||IN / IN / IN|
|JCFG0/1/2||1x3 * 3||CPU/bus clock ratio setting|
|J3DS1/J3DS2||1x2 * 2||3D sound card select|
|3D Sound Card||J3DS1||J3DS2|
Warning: production boards have different jumpers for
DIMMs with 168 pins can contain 1 or 2 banks of memory. Usually single sided DIMMs have 1 bank of memory, while double sided DIMMs have 2 banks of memory, but this is not always the case.
DIMMs provide a 64 bit wide path to the memory. With 8 bit wide ICs (e.g. 2Mx8 or 8Mx8) each bank on the DIMM contains 8 ICs. With smaller (e.g. 4Mx4) or wider (e.g. 4Mx16) ICs, you need more or less ICs to fill each bank on the DIMM.
The GG2 supports up to 512 MB of SDRAM in 4 banks (i.e. 2 DIMM sockets). The GG2 supports SDRAM with 2 internal banks only. If you have SDRAM with 4 internal banks, you can use half the amount of memory only, or none at all if you have back luck!
The internal SDRAM banks are used to implement on-chip memory interleaving and are the reason for the higher performance that can be achieved with SDRAM, compared to older memory technologies. Read more about SDRAM in this announcement from IBM from 1996.
Later SDRAM could have 2 or 4 internal banks (IBM and HP). To support this, an extra bank select line BA1 was added in addition to BA0. Since the GG2 is a design from 1996 or before, it makes sense to assume it holded pace with the memory technology from that moment. Hence the GG2 does not support the BA1 bank select line. The memory controller in the Motorola MPC106 `Grackle' chipset (used in the Apple PowerMac G3) does support SDRAM with 4 internal banks, starting with revision 4.0 of the MPC106. AFAIK all PC chipsets that support SDRAM do support SDRAM with both 2 or 4 internal banks.
Most 16 Mb SDRAM ICs have 2 internal banks. 64 Mb ICs are available from the major DRAM manufacturers with both 2 or 4 internal banks. Since this is a PC centered world, 64 Mb ICs with 4 internal banks are most popular.
Older 64 MB DIMMs use 16 Mbit technology and are composed of 32 16 MBit (4Mx4) ICs, forming 2 banks of 32 MB (16 ICs). These will work if the 16 MBit ICs have 2 internal banks.
Things will only get worse, because of the fastly evolving memory technology and computer world. Older technology is being phased out, and you can't expect to keep on buying memory for such old machines (sigh).
You can verify whether the type of your memory at the website of the memory manufacturer. Useful links: