As its name implies, this will switch the computer to 64 mode, similar to GO64 in BASIC. You will be asked to confirm before the action is actually performed. However, THE SERVANT uses a slightly different approach when switching the computer to 64 mode. If you're not technical minded, you can just skip the rest of this explanation. You will probably not be able to detect the difference.
If you're a programmer, this feature may open some interesting possibilities. As you know, the 128 has two distinct segments of RAM memory of 64K each called BANKs. BASIC uses one bank (bank 0) to store system variables, vectors, programs and high resolution screens among other things, and the other (bank 1) to store BASIC variables. Normally, when you enter GO64 in BASIC or reset the computer while holding down the C= key, the computer will set up 64 mode to work in bank 0, and bank 1 will be unaccessible entirely as long as you stay in 64 mode. THE SERVANT however, sets up 64 mode in bank 1. This is also true with all other features in THE SERVANT that switches the computer to 64 mode.
So what? Well, using bank 1 does have a quite significant advantage: You can run 64 mode ML or BASIC programs as usual. Then, you can reset the computer, and examine the entire memory from $0400 to $feff with the monitor without corruption. Screen memory, RAM under ROM & I/O will be intact. Then you can use GO 64 from the menu to return to 64 mode, again without corruption (screen memory will be corrupted of course, because the screen is cleared in the process).
I have even more in my sleeve. Hold down SHIFT when you select GO 64, and a BASIC program won't even be NEW-ed, even variables will be intact! Even utilities will still be working! Yep, see for yourself. The only exceptions are some utilities which depend on pre-set conditions in the I/O area (sprites for example). You can run programs in 128 mode while preserving 64 mode memory, provided they don't corrupt bank 1 memory. Running 128 BASIC programs is also possible if you change the variable area. POKE48,160:CLR will protect the 64 mode BASIC area, leaving 24K for variables in 128 mode. If you wish to protect the 49152 ($C000) area as well, use POKE 48,224:CLR, leaving nearly 8K of variable space. The secret behind this spectacular feature is that the lowest 1K of the 64 memory which contains all important pointers and vectors is safe under the 1K common area which is completely inaccessible in 128 mode without the use of some ML trickery. Please note that the computer will crash (if using SHIFT/9) unless you have already been in 64 mode at least once since the computer was powered up.
To be able to exploit this feature you must be careful on how you enter 64 mode: You should always enter 64 mode by using one of THE SERVANT's features. THE SERVANT will always drop you into bank 1. On the other hand, using GO64 from BASIC, resetting the computer while holding down the C= key or boot software which autoboots into 64 mode (as many games do), the computer will use bank 0 as per normal practice.
