General Notice:
DEC Venturis 5100 (socket-5, SIS 550x) with BIOS version 2.0x appears to require manual implementation of the Revised ECHS workaround for 16-head drive geometries above 8191 cylinders.

Subject:
Legacy BIOS / large storage size compatibility issue

Issue:
The DEC Venturis 5100 BIOS has a hard drive parameter translation bug which causes data corruption with 16-head IDE geometries above 8191 cylinders.

Systems affected:
DEC Venturis 5100, 5133, 5166, 5200
Phoenix NuBIOS 4.04 core, BIOS 2.0x (2.01 ~ 2.06)

Symptoms:
MS-DOS FORMAT reports bad sectors.
CHKDSK reports phantom bad clusters.
Norton utilities show periodic cluster corruption.
Occurs with multiple storage brands.

Trigger:
Drive geometry using 16 heads and cylinder counts ≥ 8192.

Workaround (Revised ECHS):
Reduce the configured geometry to 15 heads.
Increase cylinders to maintain capacity.
1) If cylinders ≥ 8192 and heads = 16:
2) Change heads from 16 → 15
3) Increase cylinder count by 16/15
Example: 8GB CF/HDD/SSD with reported parameters 15,880/16/63 change to → 16,938/15/63.

Result
DOS FDISK, FORMAT, CHKDSK, Norton Disk Doctor, and Windows 98 FAT32 formatting all succeed without errors.

Notes
If you have a Venturis 51xx and are planning on using a drive larger than 4GB then this bug will affect you.
Drives with total capacities of 4GB or under are generally unaffected by this bug.
The maximum storage size natively supported is 65535/15/63 x 512 = ~31.7 GB
Revised ECHS is normally automatically performed by the BIOS, however the Venturis 51xx BIOS is either not performing this function or doing it incorrectly, hence the need to implement it manually.