The XSIMM6, XSIMM10 and XSIMM10ss all allow you to fit standard 30pin or 72pin SIMM modules to populate the address range between 2MB and 12MB on the X68000. There's a good page on the XSIMM10, as well as the XSIMM6, but both boards are comparatively simple compared to the XSIMM10ss.

Unfortunately, information on the later XSIMM10ss is rather thin on the ground - which is a shame as it has the most flexibility of all the models:

• Two independent 72pin SIMM sockets (Slots A and B)
• A pair of 30pin SIMM sockets (Slot C)

Because of this flexibility, the amount of possible configuration variations of the on board dip switches is huge.

These are the only copies of the manual I've been able to find - they are different to the XSIMM10 which does not have the 72pin sockets:

Note: These images were sourced from http://painkilla.egloos.com/m/2623979

Because the manual is difficult to make out, I have transcribed all of the configuration options into the table below.

Note: 'Memory Size' in the below table refers to the expansion memory size, not the entire system memory size.

You can see a few restrictions on the options:

• If using any 72pin SIMMS, you must have Slot A filled first
• 30pin SIMMS must always be fitted in pairs
• You can use the following combinations:
  • Slot A
  • Slot C
  • Slot A and Slot B
  • Slot A and Slot C
  • Slot A and Slot B and Slot C (but note that there are only 2 supported configurations in that mode)
• You cannot use the following combinations:
  • Slot B
  • Slot B and Slot C

There are a couple of variations of the same sizes - they are:

• (1) 4MBit DRAM density
• (2) 16MBit DRAM density

Note: If you want to max out the memory capacity, by far the simplest option is to stick a single 16MB 72pin SIMM in slot A.

All standard 10MHz X68000 models can use 80ns, 70ns or 60ns chips, according to the manual, but at 16MHz, it requires 70ns or faster. There aren't any details for models clocked higher than that, so your mileage may vary if you have overclocked your CPU/bus to speeds higher than 16MHz.

The manual also makes reference to an xsimm.x utility, but I can't quite make out what it is supposed to do - whether it tests the onboard ram or is just documentation. As it stands, we don't know where to obtain a copy of these files.