I figured out what to do with that 4th DIMM slot...

[CaoCao]

There is this invention called SATADIMM and you can buy special SSDs that fit in DIMM slots
Available in 50/100/200GB sizes
http://www.vikingmodular.com/products/flash/satadimm.asp

[philipma1957]

most likely cost as much as the macpro you are putting it into! you know two of them as a raid0 boot drive in a 12 core 2.93 along with 6 8gb sticks of ram would be quite a machine

[WardC]

Hmmm...I wonder if that will be bootable?

Does anybody remember "RAM Disk" on the old school PowerMac machines in Mac OS 7 - 9? You could allocate part of your RAM as storage space and store files on the RAM. It was ultra-fast, but it got wiped out every time you restarted your machine. This is not actual RAM, but SSD Flash RAM. I wonder if this will be a bootable solution and if it will be much faster than a standard SSD. My SSD is the OWC 120GB and uses the Sandforce controller, has a max read/write speed of 285MB/sec. This thing could be able to read/write over a gigabyte a second, that would be amazing. You could run your whole system off just the base 50GB model and install it in RAM slot 4. Very cool. Hope it's Mac Pro compatible.