The Bendix used a magnetic drum Each memory line had a read head and a write head. Normally whatever was read would be written immediately, and would then travel around with drum rotation until it got bach to the read head and repeat the cycle.
@hendrikboom3 if its encoded magnetically though why would it have to read and re-write the byte. If the byte is unchanged cant it just stay on the drum head as-is? Again unless im missing something this just sounds like a hard-drive platter to me.