Back in the day, my college campus mainframe, a Burroughs B6700, had (in addition to its more conventional "disk pack" drives) a head-per-track (HPT) drive. The disk was several feet in diameter and the whole surface was covered with read/write heads (they didn't need to move).
Can't find specs on the B6700 version, but here's a blurb about the older B5500 version (from http://www.retrocomputingtasma...)
The powerful advanced systems concepts of the Burroughs B 5500 are fully complemented by the revolutionary Burroughs On-Line Disk File subsystem. With its "head-per-track" design, the Disk File provides all-electronic access to any record throughout the file in an average of 20 milliseconds.
File organization, programming, and use are simplified because access is entirely by electronic switching, with no moving arms, card drops, or the like. Each record segment is equally available regardless of physical location on the disks. Multiple segments can be transferred with a single instruction.
Module size is four disks totalling 9.6 million alphanumeric characters of information capacity. Up to 100 of these modules may be used with the Burroughs B 5500, effectively extending the memory of the computer systems by almost a billion characters. Transfer rate is 100,000 characters per second.