A lot of trading is indeed done by minimally supervised computers, i.e. a human only looks at the computer if alarm bells ring. Source: was one of those humans

How often are the models that drive algorithmic trading updated?

The pipeline for a given piece of research to get into production tends to be several months. Therefore, a small firm with only a few researchers might update between once and a few times a month, and a larger company it might be several times a week. It's rare to update the model more than once a day, since it'll normally be updated outside trading hours.

Sure, while humans are critical to maintaining the infrastructure of the various markets, but we are beyond the days where markets were tracked on a chalk board. The NASDAQ is very much running on servers from an undisclosed data center off route 95 in New Jersey.

Not undisclosed, primary is Equinix NY11:

https://www.nasdaqtrader.com/Trader.aspx?id=POPs