A4.0 Legacy-Free PC System Requirements

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A4.0 Legacy-Free PC System Requirements

This section describes additional requirements or exceptions to the requirements defined earlier in Section A1.0.

A4.1 Legacy-Free PC System - Windows Compatibility

A4.1.1 ACPI legacy-free support is reported as described in "ACPI Changes for Legacy Free"

[BIOS-0015; SDG3:27, 28]

  • LEGACY_DEVICES flag is set to 0 in the ACPI FADT as defined in ACPI section 5.2.1.

  • ACPI reset mechanism as defined in ACPI section 4.7.5.

  • 8042 flag is set to 0 in systems that do not include an 8042 controller; value is set to 1 in a mobile or desktop system that includes an 8042 controller.

  • Debug Port Table in the BIOS, as described in ACPI section 5.2.11.
A4.1.2 Plug and Play detection does not report the presence of Super I/O-dependent components

Based on addresses and exceptions listed in A4.1.3.
A4.1.3 No components claim to use the restricted port addresses


Restricted addresses:

COM = 2E8-2EF, 2F8-2FF, 3E8-3EF, 3F8-3FF
LPT = 278-27A, 378-37A, 3BC-3BE
Sound Blaster = 0220-022F
Joystick/game port = 0x200-0x20F
MPU-401 (MIDI) = 0330-0331
FDC = 3F0-3F7
Keyboard/mouse controller = 0060, 0064

The following exceptions apply:

  • An internal COM port header can be used as a debug port solution if the COM port is not exposed to the end user and does not use the I/O addresses listed in this table; these listed addresses must be claimed in the BIOS but not used. The relocated I/O address must be reported in the ACPI Debug Port table.

  • Systems that use the 8042 controller internally can use the related restricted addresses if the 8042 flag is set to 1 in the ACPI FADT. The 8042 flag must be set to 0 in systems that do not include an 8042 controller.

  • Systems can provide Super I/O-based IrDA support through the year 2001. Both desktop and mobile PCs can use the 8042 controller internally, but must not include external PS/2 connectors. Legacy-free systems that use the 8042 controller internally must set the 8042 flag to 1 in the ACPI FADT.

  • Windows Me: A system that does not have an 8042 controller must reserve I/O addresses 0060 and 0064 as reserved motherboard resources. Failure to reserve these I/O addresses will result in display of a false device in Device Manager.
A4.1.4 Support required interrupts


Required interrupts:

INT 8, INT 9, INT 10, INT 11, INT 13, INT 19, INT 1B, and INT 23
INT 15 subfunctions AH=C0, 4F, 87, 88 and AX=C2xx, E820, E801
INT 16 subfunctions AH=00h, 01h, 02h, 10h, 11h, 12h
INT 1A subfunctions AH=0x and AX=B1xx

See details in Table 2 at http://www.microsoft.com/hwdev/NewPC/LF.htm.

A4.1.5 Legacy-free debug interface per Debug Port Specification and FAQ A1.5.16

[SYS-0046; SDG3:15; FAQ A1.5.16]
A4.1.6 When 8042 is not present, A20M# is de-asserted (pulled high) or removed, with no way to mask the A20 address line


If A20M# generation logic (8042) is not present in the system, A20M# must be terminated in a deasserted state to the processor. If 8042 is present, connect in the standard legacy manner.

A4.1.7 Interrupt handlers preserve values in all registers

As described in A1.4.9.
A4.1.8 BIOS initializes USB Host Controller during boot process

The USB host controller must be in IRQ mode for keyboard and mouse input during real mode and safe mode. However, this can potentially cause the system to stop working when the system is running Windows 2000 if the interrupt is shared with the boot device and the host controller generates an IRQ before the USB ISR is chained.

The solution is for the BIOS to add logic to the ACPI Enable routine to turn off the IRQ-enable bit in PCI Config space for the USB host controller.

A4.2 Legacy-Free PC System - Industry Standards

A4.2.1 “ACPI Changes for Legacy-Free PCs”

[BIOS-0015; SDG3:27]
A4.2.2 Debug Port Specification, V. 1.0 or later

[SYS-0046; SDG3:15]

A4.3 Legacy-Free PC System - Quality

WHQL Test Specification References:
Chapter 18, Legacy-Free Test Specification

See A1.3.

A4.3.1 SEE A4.4.9
A4.3.2 SEE A4.4.10

A4.4 Legacy-Free PC System - Windows Experience

Design Guideline References:
PC 2001 System Design Guide, Chapter 3 -

New docking stations designed for legacy-free mobile PCs must follow these requirements.

A4.4.1 No external serial, parallel, or PS/2-compatible ports and no ISA-based game ports or MPU-401 (MIDI) ports available for external connection or detected by the operating system

[BIOS-0045; see also FAQ A4.5.2]
A4.4.2 Two USB ports in all desktop systems

See also A2.4.1.

If only two USB ports are provided, system provides at least one accessible USB port supporting end user expansion when keyboard and pointing device are attached.

Mobile PC Note: A mobile PC must provide at least one accessible USB port [MOBL-0063]
A4.4.3 System includes a bootable CD or DVD device

[BIOS-0005.1; SYS-0039; MOBL-0072]

Mobile PC Note: See FAQ A4.5.3.
A4.4.4 No FDC detected

[SYS-0040, BIOS-0045]

See A1.4.8.
A4.4.6 Peripherals provided with the system use non-legacy connectors and do not depend on real mode for installation or configuration

[WL-5; SYS-0042]

Keyboard and mouse must also use non-legacy interfaces.

A4.4.7 External input devices included with the system are HID compliant


For example, keyboard, mouse, or game controller.

A4.4.8 MS-DOS is not required to install or run any utilities, games, or other software provided with the system


Exception: Software on the recovery CD provided for Windows Me.

A4.4.9 No BIOS boot dependencies on ISA or other legacy devices, and no ISA-related components appear on BIOS setup screen

A4.4.10 BIOS supports USB input devices at boot, and does not include hardware emulation of the 8042 controller in systems where no 8042 controller is present

See details in Table 2 at http://www.microsoft.com/hwdev/NewPC/LF.htm or in Appendix A of PC 2001.

A4.5 Legacy-Free PC System - FAQs

A4.5.1 Current general FAQs

See http://www.microsoft.com/winlogo/hardware/system/.
A4.5.2 Early legacy-free systems [Clarification]

Removal of legacy components from the system involves two considerations:

  • The component is removed from the user’s perspective -- for example, slots, ports, and so on.

  • The operating system doesn't detect the presence of the component.

For example, "No FDC" means that the operating system does not detect the presence of the FDC and nothing uses the related restricted addresses.

However, the physical internal part does not need to be removed -- for example, removal of the Super I/O chip is not required; however, the physical ports must not be present on the system or detected by the operating system.

A4.5.3 CD or DVD drive requirement [Clarification]

For legacy-free mobile PCs, form-factor/size issues may preclude providing a built-in CD or DVD drive. In such cases, the requirement to include a CD or DVD drive can be met by offering external CD/DVD products that the user can choose to purchase separately and that attach to the mobile PC, docking system, or port replicator through an interface that allows the CD or DVD drive to act as a boot device.

In addition, systems designed to exclude user access to removable media do not have to meet the requirement to include a CD or DVD device. However, all systems (including those that do not ship with a CD or DVD device) must still comply with the requirement for BIOS boot support.

FAQ date: September 1999
A4.5.4 Debug solutions for Non-Legacy PCs [Clarification]

See FAQ A1.5.16.

A4.R Legacy-Free PC System - Future Requirements

Announcement of additional future requirements will be published at http://www.microsoft.com/winlogo/hardware/system/

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A4.0 Legacy-Free PC System Requirements

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