After reading the i860 meminfo problem this morning, I became curious. I did cat /proc/meminfo on my Athlon-900 machine with a Gigabyte GA-7IXE motherboard (AMD 751/756 Chipset). It had exactly the same problem. It reported a total of 64M when I had 128M installed. I added the append line as instructed and rebooted the machine. The mem total was then correct!
I forgot to mention that I use S3 Virge video card in the AGP port on the Gigabyte motherboard.
Another motherboard that doesnt get E801 memory reporting right. mem= is the right answer. 2.4 will use the E820 interface which should work right (since windows uses it)