...like ifort, will the efficiency be promoted a lot even without rewriting codes? That depends on what Fortran 77 compiler you have been using. There are some old benchmarks at http://www.polyhedron.com/pb04/win32/f77bench_p4.html showing Intel Visual Fortran to be faster than g77. and in what degree the efficiency will be promoted if I further rewrite all the codes in f95 style and ...

...> that it depends on the code, the cpu, etc. On a scale of 1 to 10, how efficient is g77 -O3 under linux ??? In the 2004 Fortran 77 Polyhedron Benchmarkshttp://www.polyhedron.com/pb04/linux/f77bench_p4.html, on Intel Pentium 4 Linux the geometric mean execution times for 8 programs were (in seconds) Absoft 33.18 G77 43.87 Intel 27.45 LF95 38.44 ...

... on the code, the cpu, etc. On a scale of 1 to 10, how efficient is g77 -O3 under linux ??? In the 2004 Fortran 77 Polyhedron Benchmarks http://www.polyhedron.com/pb04/linux/f77bench_p4.html, on Intel Pentium 4 Linux the geometric mean execution times for 8 programs were (in seconds) Absoft 33.18 G77 43.87 Intel 27.45 LF95 38.44 NAG 39.79 Pathscale 37.21...