Chad (paper) device which will not punch a complete circle in the tape but, instead, will only cut approximately three-quarters of the circumference of a circle ... thereby leaving a movable, or hinged, lid of paper in the tape." In the "New Hacker's Dictionary", two unattributed and likely humorous derivations for "chad" are offered, a back-formation from a personal name "Chadless" and an acronym for "Card Hole Aggregate Debris". Other etymologies claim derivation from the Scottish name for river gravel, "chad", or the British slang for louse, "chat". When a chad is not fully detached, it is described by various terms corresponding
Punched card input/output CPM: The number of cards which can be read or punched in one minute. Card reader models vary from 300 to around 2,000 CPM. If all columns of an 80 column card encode information this translates to approximately 2,500 characters per second (CPS). Cards may be read using mechanical "brushes" that make an electrical contact for a hole, and no contact if no punch, or photoelectric sensors that function similarly. Timing relates the signals to the position on the card. Cards may be read serially, column by column, or in parallel, row by row. Card punches necessarily run more slowly