This is an interesting feature. It will load the first program off a disk, switch to 64 mode, and run it as a BASIC program. Thereby, you can use the speed of your 1571 or 1581 to load the program before actually switching to 64 mode. This is especially advantageous with bigger programs. In fact, this feature can perfectly load programs of up to 63231 bytes in size, the equivalent of 249 disk blocks. This is a great boon if you own one of those C64 freeze cartridges. If you're using a 1571 disk drive, it will remain in 1571 mode, so you can easily enjoy it's full capacity in 64 mode as well.
SPECIAL NOTE to JiffyDos users: When JiffyDos is enabled, leaving your 1571 drive in 1571 mode while the computer is working in 64 mode will make it as slow as a stock drive. Fortunately, a JiffyDos equipped drive can still use both sides of the disk, even when it is switched to 1541 mode. It is therefore feasible to switch your 1571 to 1541 mode after the computer has switched to 64 mode. This can easily be accomplished by resetting the drive (s). If you have an 128D, you will find a small reset button on the side of your computer. Please refer to the computer's manual to find the exact location. If you have an old flat 128, you may want to buy or make a one yourself. JiffyDos users might prefer the next menu selection (Load "*",64) since your disk drive will be equally fast in both 128 and 64 mode. It will in most cases eliminate the need for a disk reset button.
