On Mon, 16 Aug 2010 14:26:32 -0400, John Ferrell
wrote:

As I recall, the cores for the 3-wire scheme needed to be held to very
tight specs so that they not only worked but worked with the same
timings as the others in the array.

Even in the 4-wire scheme manufacturing would hand select drivers &
sense amps to build an array that would work. That was a problem in
the field because sometimes a tech would swap everything swap able
from a broke array to another machine which was working. Then there
were two systems down hard! Time to send out for food, we are going to
be here a while....!

Towards the end of the IBM 360 cycle production had reached the point
where hand selection was not normally required, but it did not start
that way.

I believe that adding a 64K array to an existing 64K storage module on
an IBM 360/40 in 1966 cost the customer $75,000. For reference, I
think a new Ford Mustang cost $2500. IBM had a big campaign to
dehumanize the machinery, memory became storage and you no longer
crippled circuits you disabled them!



IIRC, a meg of memory for a 370/145 cost close to a $1 per byte,
installed.