Reading ancient paper digital media (was Re: Hamurabi Focal source)

On 31 Mar 2010 at 21:54, Fred Cisin wrote: The CDC 405 uses two rows of photodiodes and compares the read reslts as the card moves through. If the card slips, a read compare results. Two photodiodes are used at the front of the read station, positioned between rows. As the card edge moves through, the first diode, then the second diode is interrupted. If this doesn't happen, a fault is generated. Although the card feed is performed with a vacuum capstan, which always has vacuum applied (unlike the capstans in the 6xx tape drives) , pinch rollers move the card through the read station. Watching the thing read at 1200 cards per minute is pretty impressive. Another aspect that's interesting is that the top and bottom of the read station throat are wider than the middle section to accomodate dog-eared cards. --Chuck