It had a 7 inch CRT with 640x480 resolution.
For Alan Kay's talk they removed some limits of the original hardware, like screen size, processor speed, memory limits and storage (floppies in the original). They found that without these limits the experience was actually better than more modern Smalltalks in some ways. Sort of like using a 1980s 8 bit microcomputer with a modern SD card.
There’s also an Alto mode https://codefrau.github.io/Smalltalk78/?alto which is closer to what folks used to work with back then