[acomjean]

I think it “creative computing” or nibble magazine that had a postcard where you could check off interests and send it back. I did this in middle school and would occasionally get mailings about products (and credit card offers).

Magazine ads where the way to get targeted views.

[TheOtherHobbes]

That was a standard system in the magazine trade back then. It was part of the service to advertisers. They would collect all the queries for each advertiser every month and pass them on.

Those ads were unbelievably lucrative. Each page cost thousands of dollars, and there were hundreds and hundreds of them, plus smaller classifieds. Freelancers were paid fairly generously, but that outgoing was a drop in the ocean compared to the monthly ad income. Byte was posting profits of around $10m/year in the 80s.

Edit to add: many readers saw the ads as informative rather than intrusive and distracting. This was partly because many were creative and fun, but also because they went into far more technical detail than you'd see today, so they were almost a supplement to the official written copy.