...plus 6 and 8 cylinder versions, mostly used to power switchers (shunters) e.g. the SW1000/1001 series.
From the
645 Wikipedia page:
One of the things that customers like about the EMD engines is that they have fabricated (rather than cast) crankcases which can be repaired by welding when they develop fatigue cracks. This is a major reason there are lots of old EMD locos still running around. GE engines of the same vintage use cast crankcases, which tend to have to be scrapped once the cracking gets too bad, quite often resulting in the scrapping of the host loco as well (as a replacement crankcase or engine is expensive, I assume).