Engineer identifies and explains every '90s computer seen in Jurassic Park

Yes, it was, in fact, a Unix system.

Everything in the set was real. We couldn’t fake any of it, because audiences are so sophisticated now in their knowledge of computers. All told, $875,000 worth of computer hardware loaned by Silicon Graphics, $350,000 worth from Apple and some $500,000 in additional hardware and software went into equipping both the set and off-stage control room.

The Ars article is just a summary of this: https://fabiensanglard.net/jurrasic_park_computers/index.html