Hello, , you wrote:" Because of singularities of command system BESM-6, those extracodes reminded the additional built in instructions, than, for example, function invocation in MS-DOS by means of INT 21H really more. The sense of the term "extracode" is quite transparent: this extension of command system to create from the real machine the virtual machine for the given language, for example, the Pascal-car or the Lisp-car ". The Most common value of the term"extracode"in BESM-6 was"system function", as well as in any other OS. Any basic"singularities"of command system there was not - simply under the operation code it has been selected six fixed discharges, 40 commands have been defined, and the codes 050-077 (octal) were used under those extracodes of OS. Thus even the structure turned out very similar: in OS of DisPak the most"running"extracode was 050 (hundreds different functions, as well as in int 21h), and on remaining it has been hung up much less functions, as on int 2ah or 2fh. The difference was only that the operation code in an extracode of OS of DisPak was normally transferred in an address part of a command while in a command int parameters it is not provided, therefore the code was transferred in AH. Never heard about usage of extracodes BESM-6 for implementation of "virtual machines" of high level - in the main local OS of DisPak interception and handling of reserve commands were possible only at kernel level, handling transmission on the user level created very big overhead charge, therefore was used only for exception handling. For implementation of "macrofunctions" was much cheaper to fulfill a normal call. Well and it is a little strange to see reasonings of the author on any "optimization" near to a sentence about usage of extracodes. Any extracode (that is, the reserve code of hardware operation) on determination causes an exception which handling involves a noticeable overhead charge. Constructed on such principle virtual machines will be either simply slow, or extremely slow - that is, fits unless for the demonstratsionno-educational purposes.