document onto cards by pressing keys on the keyboard. Keying data in this manner
can be costly and time-consuming, with punch-in rates of 120-150 cards per minute.
Once the data are keyed in, punch cards can be handled quite fast, with reading rates
of over 1,000 cards per minute being possible for optical readers. A light source on one
side activates a photo detector if there is a hole (a binary 1) to run through. The
detector is not activated if the card face is present (no hole, a binary 0). The brush type
card reader unit is slower, with rates of only 200 cards per minutes. If the brush goes
over a hole, it makes contact with a metal plate and passes this on as a signal of a
binary 1 being read.
Figure 2-11. Punch card ('field' and "record" are explained in figure 3-2 of AMEDD
Computer Literacy II).
Figure 2-12. A keypunch machine.