A method of configuring IA-32 computer resources accommodates multiple operating systems and memory sizes automatically. If total available physical memory does not exceed 4 GB, then the minimum required memory-mapped IO size is rounded up to the next multiple of 128 M. Otherwise, it is rounded up to the next multiple of x, where x is a function of the number of DIMM socket pairs available. TOLM is set to 4 GB minus the rounded memory-mapped IO size. For operating systems that can address only up to 4 GB, the method chooses an acceptable value for TOLM because the granularity used to choose it is reasonably small--128 MB. For operating systems that can address more than 4 GB, the method chooses an exceptionally good value for TOLM: Regardless of the amount of memory available, the BIOS can define caching characteristics for all of the memory using at most 6 MTRR pairs.