Hi I've search the website and the manuals and can't get an answer, i would phone up but as it's out of hours i thought i'd ask here first. I am using RTL-ARM and the FlashFS supplied by Keil on external Flash chip in my system. I can't determine from the documentaion if a file can be modified eg. opened with fout=fopen(filename,"a") changing the file pointer with fseek and then overwriting data using fwrite? Thanks Luke