but FredlFesl : your improved / modified and untested version writes Only 1MB to FFile
i mean the FFile will only hold 1MB of the Source Stream not the Whole Stream size .
No. It writes the whole file. Notice the "REPEAT UNTIL" loop. It reads 1MB data from the source and appends it to the file. Then in reads the next 1MB.... until there is no more data in the source.