segments and initialization
 

Hello All,

I have a question concerning setting up the code segment. I'm curious about what is being done in this code excerpt. I've tried to search and find documentation about it and have been unsuccessful.

mov bx,256
add bx,OFFSET endprog
add bx,OFFSET enddata
shr bx,1
shr bx,1
shr bx,1
shr bx,1
inc bx
mov [cs:ssize],bx
mov ah,setblock
int dos.

I understand the pure mechanisms of the commands but lack the understanding as to what purpose these commands perform.

Bx contains a value dictated by the programs locations, but then it's
divided by 16? I understand that this divides it by a paragraph. Then
it's incremented. And then moved into a code segment offset ssize. And
what is being done when the interrupt to the dos routine is performed?

I hope that I have not missed some obvious clue

Thank you so much,
Sabre1985