That's higher than I would've expected for the time. That's more than half as many pixels as a Switch screen. I was born 11 years after this and I remember using 800x600 as my main desktop resolution.
On that note, anyone know of the reason for the weird resolution of 808x606 instead of a more round number like 600x800?
I can only find this document:
"The display controller handles transfers between the main memory and the CRT. The CRT is a standard 875 line raster-scanned TV monitor, refreshed at 60 fields per second from a bit map in main memory. The CRT contains 606 points horizontally, and 808 points vertically, or 489,648 points total"
https://bitsavers.org/pdf/xerox/alto/Alto_Hardware_Manual_Au...
which explains more detail but doesn't really explain how they arrived at those numbers. I assume it's something to do with vblanking or something but I don't understand it.