Folks, I hope this is the correct list to send to, as it deals with gcc-g77 and not the g95 project. Here's the deal: I am compiling fortran77 code I run on the athlon/pentium platform, and am now moving over to the Opteron. This code reads and writes fortran unformatted files when it starts up and ends. A great deal of time has already been spent creating these fortran unformatted files. (This is CFD, and the files are grid and solution files). The MIPS sgi machines had similar 32 and 64 bit flavors, and on those machines you could run either 32bit or 64bit codes and read the same unformatted files seamlessly. On the Opterton, this is not the case. I can use code compiled -m32, but when I use -m64, the code does not real the files correctly. I am specifying exactly the form of the data to be read, e.g. INTEGER*4 NJ,NK,NL open(unit=1,file='grid.in',form='unformatted',status='old') read(1)NJ,NK,NL close(1) write(*,*)nj,nk,nl end I compile this code chunk under -m32 and it will correctly read the file. I compile under -m64 and it doesn't. The reason is the record length marker(or whatever the proper term for this is) which is the first item of the unformatted file. I figured this out by writing a similar little stub program to make a fortran unformatted file, noting that I can read -m64 generated unformatted with -m64 code, and -m32 generated unformatted with -m32 code, but I could not switch them. I then looked at the generated files and noted that the first either 4 or 8 bytes was the record length for -m32 and -m64 respectively, and then the files were identical from that point on. What the heck: here's the code to generate a file to read INTEGER*4 NJ,NK,NL NJ = 101 NK = 101 NL = 3 open(unit=1,file='grid.in',form='unformatted',status='new') write(1)NJ,NK,NL close(1) end You can compile this with either -m32 or -m64 and note the changes. Now, is this what was intended? It would certainly be nice if the -m64 code would read -m32 generated unformatted the way the SGI's used to work. If this is the wrong forum, please point me to the right place... Mike