This is head-per-track drum/disk (none of this new fangled seeking stuff) - probably the slow tracks has a single set of R/W heads per track while the fast trac

This is head-per-track drum/disk (none of this new fangled seeking stuff) - probably the slow tracks has a single set of R/W heads per track while the fast tracks had multiple heads spaced around the drum. When I was a B6700 systems hack, mid 70s, we still had head-per-track disks for system files (and paging/swapping) and slower seeking (removeable) disk packs for system files