Hey ECE people! Surely you’ve seen the M5 museum on the way in the door.
What you may have seen, but didn’t know you saw, were these large rolls of magnetic tape. 10.5″ diameter, to be precise.
Each roll holds about 2400′ of tape. That’s, like, half a mile. Look a little closer, and you’ll see some cryptic labeling.
BPI stands for “Bits Per Inch,” and CPI stands for “Characters Per Inch,” which, because the characters are in ASCII, is another way of saying “Bytes Per Inch.” BPI and CPI convey the length of tape required to store one bit or byte of information. The tapes have 9 tracks, meaning that there are nine parallel stripes going lengthwise down the tape. Each track holds one bit, so there are 9 parallel bits across the width of the tape. SO COOL. ~Patrick