These were just glorified card sorting machines. Data and code was on them cards -- 4K was just temporary registers, which was plenty. And cores did not lose their data too easily. Manual bootstrapping was needed mostly because of programming errors or you used the expensive memory area for something else.<p>Cards were quite handy, because they were reusable. You could construct a program just using old ones. In university I remember a special box for &quot;100 CONTINUE&quot;-cards.