RSDT

The Root System Description Table (RSDT) is a data structure used in the Advanced Configuration and Power Interface (ACPI) specification. It is a system description table that contains pointers to other system description tables, such as the Multiple APIC Description Table (MADT), the Fixed ACPI Description Table (FADT), and the Differentiated System Description Table (DSDT). The RSDT is used by the operating system to locate and interpret other ACPI tables, which provide information about the system's hardware and power management capabilities.

The RSDT is located at a specific physical address in memory, which is defined by the system's firmware. The address of the RSDT is typically stored in the ACPI Root System Description Pointer (RSDP), which is located in the system's BIOS or UEFI firmware. The RSDP contains a signature, a checksum, and the physical address of the RSDT.

The RSDT is a fixed-length table, with a header that contains a signature, a length, a revision, a checksum, and an OEM identifier. The header is followed by an array of 32-bit physical addresses, each of which points to a system description table. The number of entries in the array is determined by the length of the table.

The RSDT is used by the operating system during the boot process to initialize the system's hardware and power management capabilities. The operating system reads the RSDT and the other system description tables to determine the system's hardware configuration and to configure the system's power management features. The RSDT is also used by the operating system to handle system events, such as power button presses and lid close events.

In summary, the RSDT is a critical data structure in the ACPI specification that provides the operating system with information about the system's hardware and power management capabilities. The RSDT is located at a specific physical address in memory, which is defined by the system's firmware, and contains pointers to other system description tables. The RSDT is used by the operating system during the boot process to initialize the system's hardware and power management capabilities, and to handle system events.