April 23, 2022
I’ve occasionally wondered what happened in the evolutionary process of the cursor between Engelbart and Xerox PARC, where the cursor shifted from being an arrow pointing straight up, to being angled at around 45º. There’s been some speculation, but I had yet to find a definitive answer, nor attribution as to who specifically decided to make the change. After emailing Alan Kay, I received the following response, which seems to solve most of the mystery:
The Parc mouse cursor appearance was done (actually by me) because in a 16x16 grid of one-bit pixels (what the Alto at Parc used for a cursor) this gives you a nice arrowhead if you have one side of the arrow vertical and the other angled (along with other things there, I designed and made many of the initial bitmap fonts). Then it stuck, as so many things in computing do.
Amusing that a primitive so fundamental is rather unknown! For the cursor curious, I also enjoyed this article, discussing the choices made in designing a cursor for iOS.