Jack writes:

I remember when I used to boot DOS from a ram drive... Don't ask, the
memory is vague.. I guess it worked like an SSD drive before they existed.

We had SSDs on mainframes in the late 70's - they've been around
for a long time (but prior to flash, were rather expensive - more
long the lines of Violin Memories 1010 initial DRAM-based solid state
disks circa 2007).

See StorageTek STC4305 he http://www.storagesearch.com/chartingtheriseofssds.html