Jerome Fine replies: I can't think of a device handler which I can boot that can have SET commands affect the "Resident" in memory copy, HOWEVER, the LD(X).SYS device driver is updated in memory as well as on the disk drive if LD(X).SYS is already loaded. Except for DU(X).SYS, I really can't think of a device driver where changes that are compatible with the LOADed in memory copy can't be done at the same time as the disk copy. Obviously, changing the CSR or VECTOR much be done only to the disk copy, as well as other critical values. In point of fact, some device drivers such as the VM must also be REMOVEd and then INSTALLed again. Most novice RT-11 users will not need to be aware of these things, but the few experienced RT-11 users (are there any left except for Megan and myself?) are usually aware of these problems - except when old farts like myself forget. Sincerely yours, Jerome Fine -- If you attempted to send a reply and the original e-mail address has been discontinued due a high volume of junk e-mail, then the semi-permanent e-mail address can be obtained by replacing the four characters preceding the 'at' with the four digits of the current year.