address bus address space amigaos application programming interface application software array assembly language beos bit cpu modes call gate call stack central processing unit colorado comparison of operating systems computer multitasking computer network context switch dos dos extender data execution prevention denver device driver exception handling executable exokernel general protection fault global descriptor table graphical user interface hardware abstraction layer history of operating systems hybrid kernel ibm ibm personal computer interrupt kilobyte legacy system linux loadable kernel module long mode ms-dos mac os x megabyte memory protection memory segmentation microkernel microprocessor microsoft windows monolithic kernel opensolaris operating system operating system development opteron page table paging peripheral preboot execution environment prefetch input queue reactos real mode segment segmentation fault self-modifying code smart pointer system management mode system software task state segment timeline of operating systems unix unreal mode user space virtual dos machine virtual file system virtual memory virtual tape library windows nt windows on windows