The "Intimus 007" shredders which I used had two rotating bars, one above the sheet and one below.
Each bar consisted of alternating larger diameter and smaller diameter discs. These cut the paper into narrow strips.
The discs had notches and mating projections which would cut the strips into short pieces.
IIRC, they were not considered secure enough to shred microfiche, because the chips could have readable sentences in them, so those had to go to a ball mill to be pulverized instead. But for printed paper, they were quite satisfactory.
Enjoy, DoN.