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4
Theory of Operation
This section describes the proper usage and programming of the SATA host controller by BIOS
and the operating system when the host controller is operating in compatible or enhanced
configuration.
4.1
Compatible Configuration
The compatible configuration is for the express purpose of maintaining backward-compatibility
with those operating systems that do not comprehend native mode of operation. In this
configuration, a maximum of four ATA (serial and/or parallel) devices on the primary and/or
secondary channels can be supported. This mode allows both the primary and secondary channels
to be configured for legacy and/or native sub-modes of operation.
Since the ICH5 supports up to six ATA devices (parallel + serial), it is possible for an end-user to
populate a platform with a combination of parallel and serial ATA devices. The fact that the ICH5
supports up to six ATA devices is not necessarily an issue for older operating systems; it is the fact
that both the P-ATA controller and SATA controller can be configured to consume legacy
resources (see Section: 3.1 Legacy Sub-Mode) that causes the issues (i.e., the primary and
secondary channel interfaces will attempt to share the same resources).
The compatible configuration solves this dilemma. The compatible configuration allows certain
device configurations to be accessed by software without the issue of legacy resource conflicts and
yet remain backward compatible with operating systems that don't implement native mode
functionality.
The ICH5 supports three compatible configuration options. These options are summarized as
follows and are discussed in detail in the following sections:
• P-ATA devices only (maximum of four) – Compatible Configuration Option 1
• SATA devices only (maximum of two) – Compatible Configuration Option 2
• P-ATA (maximum of two) and SATA devices (maximum of two) – Compatible Configuration
Option 3
Note: Proper support of these options requires that system BIOS provide a BIOS setup option (that is
subsequently saved in nonvolatile memory) that allows the end user to select an option that is
appropriate for their particular hardware/operating system configuration. To insure backward
compatibility with existing software, BIOS is not permitted to dynamically select a configuration.
SATA Programmer's Reference Manual
Theory of Operation
13
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