LOADALL is the common name for two different, undocumented machine instructions of Intel 80286 and Intel 80386 processors, which allow access to areas of the internal processor state that are normally outside of the IA-32 API scope, like descriptor cache registers. The LOADALL for 286 processors is encoded 0Fh 05h, while the LOADALL for 386 processors is 0Fh 07h. Both variants – as the name implies – load all CPU internal registers in one operation. LOADALL had the unique ability to set up the visible part of the segment registers (selector) independently of their corresponding cached part, allowing the programmer to bring the CPU into states not otherwise allowed by the official programming model. Usage As an example of the usefulness of these techniques, LOADALL can set up the CPU to allow access to all memory from real mode, without having to switch it into unreal mode (which requires switching into protected mode, accessing memory and finally switching back to real mode). Programs such as the pre-XMS versions of RAMDRIVE.SYS (1985), SMARTDRV.SYS (1986) as well as HIMEM.SYS (2.03, 1988-08-04; 2.04, 1988-08-17) drivers in MS-DOS, Uniform Software Systems' The Extender (1985) and The Connector (1985) for Lotus 1-2-3, Above Disk (1986) (a LIMulator by Above Software (formerly Tele-Ware West aka Los Angeles Securities Group) that converted hard disk space or extended memory into expanded memory), and OS/2 1.0 and 1.1 used the 286 LOADALL instruction. DOS 3.3 and 4.0 reserved a 102-byte buffer at 0070:0100h (which was normally occupied by DOS BIOS data) so that there was no need to save & restore it for LOADALL. Microsoft's EMM386.EXE special-cases both the 286 and 386 LOADALL instructions in its invalid opcode handler. Examination of the virtual-machine monitor code in Windows/386 2.10 shows that it uses both the 286 and the even less known 386 variant. Microsoft's HIMEM.SYS version 2.06 also used LOADALL to quickly copy to and from extended memory on 286 systems. Another interesting usage of LOADALL, laid out in the book The Design of OS/2, would have been to allow running former real-mode programs in 16-bit protected mode, as utilized by Digital Research's Concurrent DOS 286 since 1985, as well as FlexOS 286 and IBM 4680 OS since 1986. Marking all the descriptor caches in the GDT and LDTs "not present" would allow the operating system to trap segment-register reloads, as well as attempts at performing real-mode–specific "segment arithmetic" and