Editing IBM System/38 (section)

===Machine Interface===
The System/38 and its descendants use a machine interface architecture to isolate the [[application software]] and most of the operating system from hardware dependencies, including such details as address size and register size.

Compilers for System/38 and its successors generate code in a high-level instruction set known as the ''Machine Interface'', or MI. MI is a virtual instruction set; it is not the instruction set of the underlying CPU. MI operates on ''objects'' instead of traditional memory addresses or registers.<ref>{{cite book | chapter-url = http://www.cs.washington.edu/homes/levy/capabook/Chapter8.pdf | title = Capability-Based Computer Systems | chapter = The IBM System/38 | first = Henry M. | last = Levy | publisher = Digital Press | year = 1984 | isbn = 0-932376-22-3}}</ref>

Unlike some other virtual-machine architectures in which the virtual instructions are interpreted at runtime (see [[P-code machine]]), MI instructions are never interpreted. They constitute an intermediate compile time step and are [[binary translation|translated into the processor's instruction set]] as the final compilation step. The MI instructions are stored within the final program object, in addition to the executable machine instructions.  If a program is moved from a processor with one native instruction set to a processor with another native instruction set, the MI instructions will be re-translated into the native instruction set of the new machine before the program is executed for the first time on the new machine.

The TIMI (Technology Independent Machine Interface) of OS/400 is a backwards compatible extension of the System/38 MI. As a result, it is possible for a program originally developed on a System/38 to run on current [[IBM i]] hardware without ever being recompiled.<ref name="inside-as400" />