The physical memory address space on PCs is divided into distinct regions which have certain attributes. The lowest 1MB of physical memory is ``special'' in that only it can be accessed from real mode. The lowest 16MB of physical memory is special in that only it can be accessed by the built-in DMA controller. On some PCs, there may be an additional boundary imposed by the motherboard. Memory above this boundary (e.g., 64MB) may not be cacheable by the L2 cache. The base environment uses the OSKit LMM library 15 to accommodate these differences. Physical memory is managed by a single LMM malloc_lmm with separate regions for each ``type'' of memory. Hence, LMM allocation requests can be made with appropriate flag values to obtain memory with the desired characteristics.