This is not the new hard disk. Photo: Flickr/Alpha Six

“Memory is the new disk,” Jim Gray liked to say.

The database pioneer died in 2007 after he was lost at sea, but like so much of the man, his words about memory and disk live on. Fred Holahan, the vice of president of marketing at VoltDB, uses those words in plugging his company — an outfit offering a database that stores all data in memory rather than on disk — and, yes, they describe a larger movement across the database business and beyond.

In addition to VoltDB — the latest venture from another well-known database pioneer, Mike...