Common Blocks in Fortran 77

http://www.nationalfacility.apac.edu.au/training/FortranAdvanced/slides/slides.017.html

Common blocks are a Fortran 77 construct, providing areas of shared storage between different subroutines. eg.

program main
   integer :: a, b
   real :: c
   common /d/ a, b, c
 ...
end program main

subroutine foo()
   integer :: a, b
   real :: c
   common /d/ a, b, c
 ...
end subroutine foo

the common storage is called d and contains the integers a, b and the real c. Setting these variables in one routine changes it in all. Common blocks are now replaced by modules in Fortran 90.