This ROM modification changes the 5.25" Floppy Drive ProDOS/SmartPort block device in the UDC's Firmware from 280 blocks to 320 blocks, or in other words from 35 to 40 tracks. Yes, with this version of the UDC's ROM you can actually have more storage space on your ProDOS formatted 5.25" disks!
The Floppy Drive used must also support 40 tracks for this ROM to be useful.
UDC 40-Track Modification ROM by David Wilson.
The ROM file is also available >HERE< for free if you wish to burn your own.
Below are some pictures of the two versions of the UDC that were made.