Each track is broken up into sectors. A sector is the unit of disk transfer. DECStation 5000 is a standard workstation available in 1993. Plus, many operations require multiple disk accesses. Is just a sequence of sectors.
Adjacent cylinders are in sequence.
OS may logically link several disk sectors together to increase effective disk block size. There is a piece of hardware on the disk called a disk controller. OS issues instructions to disk controller. Can either use IO instructions or memory-mapped IO operations. In effect, disk is just a big array of fixed-size chunks.