have a few questions a bout my DM41L

[GMCVANGUY]

Have been enjoying my new, DM41L as well as an ebay find of a hp41c with a survey pack, have a few questions after using the dm41.
How much memory does it have, how do you access the extended memory, how does the number of registers relate to the lines of program code.
Several of the survey programs I have found are in excess of 400 lines. Would like to be sure they fit before I spend a few hours typing them in.

Am a surveyor and will admit to righting several programs, nothing as fancy as the HP survey pack provides but they work for what I need, would like to back them up. Have connected it to my computer and set the time and date. and unintentionally reset the calculator a few times but don’t know how to back up a program or all of the memory.
And is it possible to load a program, a raw file

Most of my Hp calculator use has been using an hp200lx for the last 20 years and will always be my go to calc. but the 41DM was my reward for figuring out how to use the hp35. which is about 50 steps back from my 200lx . It wont replace my 200lx but will spend a lot more time is my shirt pocket and getting used than the 35s will. Have to have the 35s to take surveys exam. otherwise would keep with the 200lx and never look back.