Ampex must have used the term on a number of products.
I've got a
full-length ISA card here from Ampex with a ROM labeled "Ampex
Megastore". External interface is a 50 pin header. It appears to be
a SASI interface card.
That's what google told me: 50 pin, "megastore", ISA, SASI, questionable
ESDI etc.
The thing I have is a 19" device approx 2/3 height of a pdp8/e, RL02 and
friends.
-- Philipp