ACPI device description tables such as DSDT and SSDT are comprised of device scopes and methods that define the capabilities and resources of an ACPI device. For scalability purposes, the ACPI devices are categorized in a manner that they can be easily plugged in and out of UEFI FW.
These devices are silicon specific and are assumed to not change with different SKUs and stepping of the silicon. These devices will become part of DSDT as it is a mandatory table containing the fixed devices for the systems.
The number of silicon devices present in the DSDT will be decided by the scope of minimum and full build.
These devices are SKU specific and are assumed to change based on various SKUs. They are considered to be dynamic as they can be enabled/disabled/modified based on setup knobs or softstraps etc.
Because of their dynamic nature, these devices are added in the Platform SSDT. Every SKU will have a unique Platform SSDT installed. It will only contain devices present on that platform.
These devices are board specific and are assumed to change based on the various board SKUs. These devices will also become part of SSDTs. These devices can have an SSDT of their own or get added to the platform SSDT depending on their availability on multiple SKUs. A fairly common board device will be added to the platform SSDT and the other devices can have a SSDT of their own.
These devices or methods are optional as they are exposed to handle certain advanced features. They will be added to DSDT or SSDT depending on the device they are being added for. For example a special DSM (device specific method) is to be added for an Audio codec, then it will fall under the Platform/Board SSDT.