Once in a while you begin to suspect your RAM and want to test it. Booting off floppy (huh?) or USB can be a pain, and cutting an ISO gives WALL-E unwanted business. The easiest option on Debian is to apt-get install memtest86+ and then add to your grub's (I use Grub4Dos) menu.lst the following lines
title Memtest86+ find --set-root /boot/memtest86+.bin kernel /boot/memtest86+.binand boot to this utility.
(2020/12/15) Now of course there's memtester which does not need you to reboot the computer but cannot test all areas of RAM.