This item is from the Yet Another Enhanced IDE/Fast-ATA/ATA-2 FAQ, by John Wehman and Peter den Haan with numerous contributions by others. (v1.92).
The latest revision of the standard is ATA-3. Key features include: improved reliability, especially of PIO mode 4; a simple password- based security scheme; more sophisticated power management; and Self Monitoring Analysis and Report Technology (S.M.A.R.T.), allowing the drive to warn you about certain types of impending failure.
ATA-3 does not define any faster modes. Even though some manufacturers were once marketing "mode 5" equipment, there will never be a PIO mode beyond ATA-2 PIO mode 4.