No whole phisical memory, no 64bit

[szzsqing1]

Thank you. I use only live systems run from ISO files with manually installed GRUB2. Reading your post I found the solution. I should have used linux64 (instead of linux) in my grub.cfg file. By this way Knoppix see 3,7G total memory as SystemRescCD does.
But quite many times the system crashed at "System setup OK" (boot screen). No matter if I used knoppix or knoppix64 cheatcode. The solution was applying "nozram". So, the right (hope) menuentry in the grub.cfg file:

menuentry "KNOPPIX_V7.6.1DVD-2016-01-16-EN 64b hu London" {
    set ISO=boot-isos/KNOPPIX_V7.6.1DVD-2016-01-16-EN.iso
    loopback loop /$ISO
    linux (loop)/boot/isolinux/linux64 knoppix nozram bootfrom=/dev/sda1/$ISO nostartsound noeject noprompt lang=hu tz=Europe/London --
    initrd (loop)/boot/isolinux/minirt.gz
}

Also sometimes (this is not related to 64bit kernel) after the boot screen does not start X but a black monitor. This issue I resolve by pressing the power button. Then X starts...