It improves various functions of release 3.2, while also allowing for large gains in available floppy disk storage; the newer P5A/P6A PROMs in the disk controller enabled the reading and writing of data at a higher density, so instead of 13 sectors (3.25 KiB), 16 sectors (4 KiB) of data can be stored per disk track, increasing the capacity from 113.75 KB to 140 KB per disk side – 16 KB of which is used by filesystem overhead and a copy of DOS, on a DOS 3.3-formatted disk, leaving 124 KB for user programs and data. DOS 3.3 is, however, not backward compatible; it cannot read or write DOS 3.2 disks. To address this problem, Apple Computer released a utility called "MUFFIN" to migrate Apple DOS 3.2 files and programs to version 3.3 disks.