[cesarb]

> Now why is it that disks lack byte-wise resolution?

Overhead.

Each disk sector is not 512 bytes (or 4096 bytes in modern disks), it's a bit more. It needs at least the sector number (to detect when the head is flying over the correct sector), a CRC or error-correcting code, a gap of several hundred bits before the next sector (so writing to one sector won't overwrite the next one), and a preamble with an alternating pattern (to synchronize the analog to digital conversion). All this overhead would be a huge waste if the addressable unit were a single byte.