 In the early days of home micros, this was often a data cassette deck (in many cases as an external unit).Later, secondary storage (particularly in the form of floppy disk and hard disk drives) were built into the microcomputer case.Although they did not contain any microprocessors, but were built around transistor-transistor logic (TTL), Hewlett-Packard calculators as far back as 1968 had various levels of programmability comparable to microcomputers.