Hello! Give that a feature?

Nowhere else can not find a description.

I haven't seen that specific call to int 13h before. Depending on what you are trying to reverse-engineer, the code could be in the BIOS (real or virtualised), or in a software int 13h handler extension, that is loaded after boot, or .... (You know what you are doing - you haven't told us that information, so I won't try to guess. )

If I was trying to find out what that code did, I would trace the call flow for the int 13h handler. There is usually the equivalent of some type of "switch-like" statement early in the handler for different ah values - then investigate what happens with ah=0x54

thanks for responding. I thought that this forum is dead), I disassemble the secondary boot BCDW, and there I met this function. Apparently it is undocumented.

Congratulations on finding it