The small studio I worked while in high school would develop B&W on site, for color most would drop their film off at a drug store, it took 3 or 4 days for turn around. While in college we toured a color processing plant. As noted, large, really big machines. 35mm was spliced together for printing in a auto machine, don't recall the brand. Enlargements were done on Omega enlargers. On the other end processing was the custom house. The lab I used did everything by hand, from film processing to printing, cost 3 times what the drug store charged, he did b&W, color print and slide film up to 8X10. .