This happens at about 1 bit in 1015 in enterprise-class disk drives , and 1 bit in 1014 in ordinary disk drives . The UBE ( Unrecoverable Bit Error ) rate is typically specified at 1 bit in 1015 for enterprise class disk drives ( SCSI , FC , SAS ) , and 1 bit in 1014 for desktop class disk drives ( IDE\/ATA\/PATA , SATA ) .