Hitachi IC25N040ATCS04-0 - Travelstar 40GN 40GB UDMA/100 4200RPM 2MB 2.5" IDE Hard Drive Specifications page 182

The Sector Count register shall be set to specify the feature to be enabled or disabled:
Sector Count
00h
01h
F8h
F9h
A value of zero written by the host into the device's Sector Count register before issuing this subcommand
shall cause the automatic off-line data collection feature to be disabled. Disabling this feature does not
preclude the device from saving attribute values to nonvolatile memory during some other normal oper-
ation such as during a power-on, during a power-off sequence, or during an error recovery sequence.
A value of one written by the host into the device's Sector Count register before issuing this subcommand
shall cause the off-line read scanning feature to be disabled. The Device does not perform the off-line
read scanning at the off-line data collection activities which is initiated by the S.M.A.R.T. Execute Off-line
Immediate (Subcommand D4h) or automatically if the off-line read scanning feature is disabled.
A value of F8h written by the host into the device's Sector Count register before issuing this subcommand
shall cause the automatic Off-line data collection feature to be enabled.
A value of F9 written by the host into the device's Sector Count register before issuing this subcommand
shall cause the off-line read scanning feature to be enabled. The Device perform the off-line read scan-
ning at the off-line data collection activities which is initiated by the S.M.A.R.T. Execute Off-line Immediate
(Subcommand D4h) even if the automatic off-line feature is disabled.
Any other nonzero value written by the host into this register before issuing this subcommand is vendor
specific and will not change the current Automatic Off-Line Data Collection and Off-line Read Scanning
status. However, the device may respond with the error code specified in Figure 133 on page 181.
Feature Description
Disable Automatic Off-line
Disable Off-line Read Scanning
Enable Automatic Off-line
Enable Off-line Read Scanning
Hitachi Travelstar 60GH & 40GN hard disk drive specifications
169