 CST addressing allows 4 of the PAST entries to be mapped at addresses 0KiB, 16KiB, 32KiB, and 48KiB, giving the 16-bit/64KiB address space.Programs which use more than 64KiB of memory must explicitly map the PAST entries they require at any moment into their 4 CST entries, although Nucleus will automatically map different code segments into the CSTs.PAS addressing allows programs to view their address space as a flat 32-bit address space, with successive PAST entries appearing every 16KiB, and Nucleus performing the PAST entry segment mapping automatically.