I've occasionally wondered what happened in the evolutionary process of the cursor between Engelbart and Xerox PARC, where the cursor shifted from being a dot or an arrow pointing straight up, to an arrow 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:
From: Alan Kay
To: James Hill-Khurana
Date: May 4, 2020
Subject: Re: History of the Mouse Cursor
Hi James,
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.
Cheers,
Alan
...and a later email with an excellent observation:
From: Alan Kay
To: James Hill-Khurana
Date: May 5, 2020
Subject: Re: History of the Mouse Cursor
Hi James,
Stickiness can be a boon and a sludge. We have to decide how to use our memories and what we've learned, and not be ruled by them.
Cheers,
Alan
See also: Design for the iPadOS Pointer & Mouse Cursor History