English: A magnetic storage card (front and backside) for Hewlett-Packard (HP) programmable calculators HP-41, HP-65, HP-67, and HP-97. The arrows with numbers 1 and 2 on the left and right edges indicate that the card may be used in both directions in order to use the full storage capacity - which was, however, very small with only about 500 Bytes or 0.5 Kilobytes (already using both directions). HP invented these cards with the programmable calculator HP-65 in 1974, which was the first of its kind on the market. The necessity of such a storage device - which would be comparable to the later diskette drives or much later USB memory sticks - was that the main memory (RAM) of the calculator was emptied when the device was powered off, hence all program data and application data was lost, unless stored on such a card.