DEC card form factor

Many different DEC computers (e.g. PDP-8, PDP-10, PDP-11) used a standard set of board sizes.

The original small standard length FLIP CHIPs used a board size of 4.93 inches (from the end of the contact fingers, to the handle end of the board) by 2.437 inches (from one side to the other). From this basic size, a large array of other sizes was built up.

A board of the same width, but approximately twice as long (8.43 inches) was referred to an an extended length board; many later FLIP CHIPs used this format. A board of the short length, but twice as wide (5.187 inches) was referred to as a double height board; boards of this size are not common, but do exist. (The 'height' does not refer to the length, but to the width; this is because these board were usually mounted vertically, with the side edges on the top and bottom.)

Extended length boards came in multiples of two, four (10.457 inches) and six times the height of the small original board; these are usually called dual, quad and hex format boards.

Finally, as production processes improved, and leading signals from board to board became undesirable, even longer hex boards were introduced; these first appeared in the VAX-11/780, and were called super hex boards within DEC.

The contact fingers groups on the edge of a hex card are 'numbered' A-F, starting from the top (when the card is installed, vertically); this would be the right-hand edge, when the card is horizontal, with the component side up, and the contact fingers toward the viewer.

Within each contact finger group, the individual lands are 'numbered' from the DEC Alphabet; those on the component side are further numbered '1', and those on the solder side, '2'. I.e. with the board in a horizontal position, as described above, the right-most contact land on the top (i.e. visible) would be identified as 'AA1'.