It was done by
hand I think. Mexico comes to mind.
Some manfacturers did it by hand, some by machine. IBM had core stringing
machines during the S/360 era, for the huge stacks (about 1' by 4') used
in some of the storage units. They also had cores hand strung in the far
East, as the cheap labor was more economical than the robots.
The far east manufacture of core lead to a long-running joke
in the old mainframe days... the instance of it I will describe
was only one of many...
Anyway, when we'd boot the COPE (Harris) 1200 Remote Job Entry
Station (a PDP-8 clone), there would be a message that would
flash by on the console *very quickly*:
HELP! HELP! I'm being held hostage in a Hong Kong Core House!
Read this thinking "Mike Hunt" and "Amanda Huggenkiss" if you
don't (by some chance) get it...
-dq