I have the old Compuped Pedigree program, which goes back to 30 generations. Most other software programs end at 10-15 generations (like The Breeder's Standard, which I also have).

I have found, however, that the most drastic differences are when you reach back from 4-6 generations to 10-15 generations ... but when you reach beyond 15 generations the difference becomes negligible.

Jack