[RESOLVED]load the 1st,2nd,3rd 100mb into an array

[new fish]

hey guys
i have this prog that loads the contents of a file into a byte array.
this is fine for a file or reasonable size, but for very large files/archives the size can be in the GB range.
i've discovered that a byte array can only hold 4gb of data,
the largest file i've loaded is 1gb, and it means that the prog uses a full 1gb of ram.

i'm hoping to recode the programme such that it only loads the file in 100mb chunks,
i.e. gets the 1st 100mb, does its job
gets the 2nd 100mb, does its job

so that the byte array never has more than 100mb

for now the prog loads the file into the array thus:
Get #tfilenum, , arrdata

q: is it possible to:

get #filenum, from the 1st to the 1000000 byte, arrdata??

looking forward to your suggestions, go easy, i'm a bit of a noob!