Up through the 1980's, when the exam was known as NBME Part I, it was administered on paper and most medical students took it shortly after finishing M2. By that I mean you might finish M2 on a Friday and then sit for Part I on the following Tuesday. It was P/F and that was that. Much more of a recall exam, you prepped for it by studying for the first two years of medical school.
After Step 1 debuted in 1992, it became evident that your three digit score had some correlation to your odds of passing your specialty boards on the first attempt. When PD's figured this out there emerged some pressure to allow students a couple of weeks to review before taking it. This gradually inched up over time.
I took Step 1 almost 20 years ago (got a decent score, too!). My school gave us all a generic plan of about 4 weeks, told us which books to buy (the UFAP of its day) and how many hours to study. Online question banks were fairly new, so most of us relied on hard copy materials. There were no real self assessment tools of any sophistication or widespread use.
Of course, that was back when very few people applied to more than 20 residency programs.