>> /APIC doesn't work at all without /SMP on same line. It is just >> ignored without it. >> > Are you sure of this statement? I thought that /APIC vs /PIC had to do > with how interrupts are routed and that /APIC only makes sense on > mother boards that support the more up-to-date interrupt handling. > At its root, it's a design choice that one has to make about what are the default and non-default configurations for an operating system. If you look at this from a wider perspective than merely OS/2 platform drivers, you'll find that although the various combinations are *in theory* orthogonal, in practice the choice of one generally dictates the choice of another. In Windows NT, for example, not all of the possible combinations of ACPI, local APICs, and SMP exist as HALs (e.g. HALACPI.DLL v. HALAPIC.DLL v. HALAAPIC.DLL v. HAPMACPI.DLL v. HALMPS.DLL). It's essentially a design decision what combinations to support, with what defaults, and when to say "If you don't have X then you're just going to have to do without Y as well.". What Allan is saying is that the design choice made here is that if you, the system administrator, choose the ACPI platform driver, then you get APIC and SMP as a job lot: either you have both or you get neither.