There’s a hidden, system, read-only file called boot.ini in system boot drive.

Here’s a sample to run 1 GB dual as a 128 MB uniprocessor:

[boot loader]

timeout=30 default=multi(0)disk(0)rdisk(0)partition(2)\WINDOWS [operating systems] multi(0)disk(0)rdisk(0)partition(2)\WINDOWS=”Microsoft Windows XP Professional” /fastdetect /numproc=1 /maxmem=128