When you type DOS in BASIC, a pointer is followed to a routine which loads in the DUP.SYS package of utilities. You can borrow this vector for your own use. The location of the DOS vector is in RAM at locations 10 and 11 ($0A and $0B). Since they are in RAM in page 0, you can change them to point anywhere you want. You could point it at the start of BASIC (40960) or at a subroutine you loaded into memory. Remember, all you have to do to enter the routine once you have changed the vector is type DOS. After you set 10 and 11 they will be reset when you press SYSTEM RESET unless you do the following. Locations 5446 and 5450 ($1546 and $154A) contain the value that the warmstart routine places back into 10 and 11. So if you POKE your DOS VECTOR location into 5446 and 5450 (LO-HI), you will keep your new pointer until you turn off the power.