Wasn't core memory very expensive in the beginning? It had to be hand assembled, at least in the early days. I think there was a more gradual take up than you suggest. Of course the more expensive machines which used it first saw a huge speed increase over drum main memory. When I was at university (71-74), the college's mainframe still used a drum from program overlays (probably really the virtual memory backing storage, but possibly just dumping and restoring the whole program between time slices. The machine was no slouch, it was serving about a hundred terminals and running a couple of batch streams as well (Maximop and George 2). Mid 1970s I remember seeing a small plastic pot about the size of a 35mm film canister, which was full of about 100,000 unstrung cores, they were tiny! They were used in the Marconi-Elliott 920ATC computer and also in the early Cruise missiles and some torpedoes. Ever wondered why a British submarine used a WW2 type torpedo to sink the big Argentinian Cruiser? My theory is that they were too worried about the modern torpedoes coming back and blowing themselves up, so they used one they trusted to go where it was pointed. Hopefully 25 years on, they've sorted out the terrible guidance system. Not related, but apparently the programmers were in a quandary as to what the program should do after it had issued the order to detonate. Like the old TV series 'Waiting for God'. The first machine which ICT introduced with core memory was in 1962, though physically large, the 1300 was a medium power machine, seen more as a versatile tabulator for accounts rather than scientific work, though it had a structural frame analysis package and even PERT, though I suppose that is just up market accounting in a way. Customers did all sorts of other work on it too, helping to design 'planes and even playing music on the built in speaker. There's a wonderful program called Ghost, only a half a dozen instructions, which uses the variable length of the multiply instruction to make a ghostly sound on the speaker. Its a good test of the CPU too, and can be keyed in through the control panel if need be in a minute or so. Also has drums - each one 12000 words x 48 bits run by a 3/4 horsepower motor and occupying 2ft x 2ft x 5 ft. Compared to the 8GB SDHC card for my 12MP camera which is about an inch by an inch by a sixteenth and stores 100,000 times as much in about 1 / 500,000 times the volume. And the core store is one sixth the capacity of the drum in a greater volume.