I want to open Windows Me DOS 8 IO.SYS file with an hex editor to change some ASCII strings, but the file seems to have been compressed with an unknown (for me) utility. Anybody knows how to decompress/edit it ?? Thanks a lot.

It's not compressed, it's called programming. Assembler is the most likely the name of the language. Nigel

"Assembler is the most likely the name of the language" Ja, Ja You are very funny, machine code, since it's compiled. It's compressed because it has half size than previous versions and MZ at the beginning (the decompression EXE stub).

Actually I didn't try to be funny. It's always hard to know the level of knowledge of the poster, so you can adapt your reply accordingly. I may have been fooled by your desire to edit "some ASCII strings" into a vital system file. Compression into .exe is mainly done by use of EXE2BIN. HTH Nigel

MZ is very common at the beginning of EXE DLL SCR and other types. The most likey compressor, if one was ised, would be the M$ one. A better question would be which UNcompressor to use. A have a few squirreled away and I'll look when I get time. MZ is also at the start of w98se io.sys, which seems to have the stringds not compressed. Keep in mind that regardless of whether it was written in asm and compiled or written instruction-by-instruction, if you alter anything it may blow up. So put on a full-face helmet and riding leathers. And have a CO2 bottle handy. M2

Most of Windows is coded in "C".