Features and Motherboard Layout
Courtesy of ASUS
- Next-gen connectivity – Includes extensive upgrades including onboard U.2 / M.2 slots that tap into 32Gbps of PCIe bandwidth, as well as onboard USB 3.1 Type C
- ASUS Aura – Features controllable RGB onboard lighting and 4-pin strip header that can be synced with an ever-growing portfolio of Aura-capable ASUS hardware
- Patent-pending SafeSlot – Reinvented, strengthened PCIe slot utilizes a new insert-molding process to bind the slot to fortifying metal for superior retention and shearing resistance
- 5-Way Optimization: Fan Xpert 4 – Elevates customized cooling to new heights, with the ability to detect PWM/DC fans on all headers, utilize high-amperage fans and control water-cooling pumps in software and UEFI
- Crystal Sound 3 – Gaming-grade audio with unmatched clarity featuring a new power pre-regulator for clean power delivery, which joins ASUS-pioneered noise isolation design and premium audio components
The X99-A II motherboard follows ASUS' channel-line aesthetics with a black and color scheme and chrome heat sinks. The board is designed within a standard ATX form factor, providing more than enough room for its integrated components without on overly crowded layout.
The rear side of the motherboard PCB is mostly free of sensitive components with the exception of the TPU chip underneath the PCIe slots and some small chips to the right of the CPU socket area. The backside of the CPU VRMs are covered by an aluminum plate, providing a secondary heat dissipation path for the components on the top of the board. Around the CPU socket itself, there is a grouping of small chips to its right that could pose issues if you use a CPU cooler requiring a third-party backplate.
The X99-A II motherboard includes the following ports integrated into its rear panel: a PS/2 keyboard/mouse port, four USB 2.0 ports, four USB 3.0 ports, two USB 3.1 Gen2 ports (1 Type-A and 1 Type-C), one RJ-45 port tied to the Intel I218-V controller, the USB BIOS Flashback button, an optical audio port, and five analogue audio ports. All blue colored USB 3.0 ports are controlled by the Intel Z170 controller. All USB 3.1 ports (to the left of the audio ports) are controlled by the integrated ASMedia controller. The USB BIOS Flashback functionality is tied to the lower USB 3.0 port to the left of the USB 3.1 Gen2 Type-C port.
The USB BIOS Flashback button can be used to re-flash the BIOS without having to boot the system into the UEFI BIOS interface or a command-line mode interface. Simply plug in a USB drive containing the proper BIOS file in the root of the drive into the lower USB 3.0 port (blue colored) located to the left of the red USB 3.1 Type-A port and power on the system. As the BIOS is updated, the LED flashing frequency increases. Once the LED goes out, the flash operation is completed and the board can be booted. Note that if the BIOS Flashback LED flashes for 5 seconds and then glows solid, it means that something went wrong with the flashback operation. Check the USB drive for the the BIOS file in the root and make sure that the BIOS file is named correctly. BIOS Flashback looks for a specific filename and file format when attempting to replace the on-board BIOS. According to the user manual, the BIOS file in the root of the flash drive must be named X99A2.CAP for the BIOS Flashback applet to successfully re-flash the board's BIOS.
40-lane CPU PCIe Bandwidth
Courtesy of ASUS
28-lane CPU PCIe Bandwidth
Courtesy of ASUS
The X99-A II motherboard has a total of six PCI-Express device ports – four PCI-Express x16 slots and two PCI-Express x1 slots. With a 40-lane CPU, the board supports full x16 bandwidth with a single card, x16 / x16 bandwidth with dual cards, x8 / x16 / x8 with three cards in PCIe x16 slots 1, 3, and 4. With a 28-lane CPU, the board supports full x16 bandwidth with a single card, x16 / x8 bandwidth with dual cards, x8 / x8 / x8 with three cards in PCIe x16 slots 1, 3, and 4. PCIe x16 slot 2 runs as x1 or x4 bandwidth, depending on the BIOS setting. Note that running the slot at x4 bandwidth disables PCI x1 slot 2 and the two USB 3.1 ports in the rear panel. The board's CMOS battery is between the middle of PCIe x16 slots 3 and 4, just below PCIe x1 slot 2.
The board's integrated audio components are located just above the PCIe slots on an isolated PCB, minimizing line-noise and distortion caused by other integrated components. The PCB separator line illuminates according to the color scheme configured through the UEFI or the AURA applet in Windows. The audio output header is located to the lower right of the overlay along the board's edge.
In the upper left corner of the board (and along the outer edge of the PCIe x16 slot 4) are the front panel audio header, a serial port header, a 12V RGB LED header, and the power and reset buttons. The RGB LED header can be used to power and synchronize a connect LED strip with the board-integrated LEDs.
With an RGB LED strip connected to the 12V RGB header, it becomes possible to sync the LED strip color and activity with that of the motherboard's integrated LEDs.
The power and reset button, 2-digit diagnostic LED display, trusted module port header, and a USB 3.0 header are located to the lower left of the PCIe x16 slot 4. The 2-digit diagnostic display can be used for debugging system issues during system initialization. The displayed debug codes can be decoded using the table from the motherboard manual.
A USB 3.0 header, USB 2.0 headers, external fan device header, temperature sensor header, CPU Overvolt jumper, XMP memory switch, Thunderbolt device header, chassis intrusion header, BIOS clear header, chassis fan header, front panel header, and PCIe x4 M.2 slot are located in the lower left corner of the board. The M.2 port supports M-Key style M.2 SSDs with PCIe or SATA interfaces and length of up to 110mm. The external fan device header can be used to add additional fan and temperature ports by connecting the external fan board to the header using the included cable. The EZ XMP switch forces the system memory modules to operate per their factory configured XMP settings. This functionality is enabled with the switch pushed to the right. The CPU Overvolt jumper enabled a higher voltage ceiling for the CPU Voltage (configurable via the UEFI) when enabled.
The Intel X99 chipset is cooled by a low-profile white heat sink with the ASUS corporate logo on its surface.
ASUS designed the X99-A II board with a total of eight SATA 6 Gb/s ports, one SATA-Express 10 Gb/s ports, and a PCIe x4 NVMe capable U.2 device port. The SATA-Express ports house two SATA 6 Gb/s ports each that can be used as stand alone ports, adding an additional four SATA 6 Gb/s ports to the board. All ports are controlled directly by the Intel X99 chipset. Note that the U.2 device port shares bandwidth with the M.2 device port.
The eight on board DDR4 memory slots are located directly above and below the CPU socket with support for up to 128GB of memory across all slots. Quad Channel memory mode is enabled with memory modules seated in slots 1 and 3 or slots 2 and 4 in both the upper and lower memory slot sets. The primary memory slots are slots 2 and 4 in the top and bottom slot sets (the grey-colored slots). Note that memory speeds above 2133MHz are considered overclocked speeds and are outside of the official Intel stock memory speed specifications. Directly below the lower set of memory slots are a USB 3.0 header, the primary and secondary SATA 6Gbps port block, a chassis fan header, the 24-pin ATX power connector, and the MemOK! button. To the upper left of the upper memory slots is a 4-pin fan header. The MemOK! button can be used to reset memory-related BIOS settings to defaults, useful when the system doesn't boot because of memory options set over-aggressively.
To the right of the upper set of DIMM slots are CPU primary (CPU_FAN), CPU secondary (CPU_OPT), and water pump (W_PUMP) 4-pin fan / power headers. The 4-pin water pump header can be used to power a standard 12V water pump – an AIO cooler's integrated coolant pump or a pump integrated into a DIY loop.
The CPU socket area is mostly clear of obstructions allowing use of most coolers without issue. The board was designed with a total of eight digital power phases for CPU power delivery requirements, which should provide more than sufficient power under any situation. The VRMs are cooled by a large passive aluminum heat sinks to the right of the CPU socket. Notice that the VRM's chokes have integrated metal covers with ridges to aid with passive cooling of those components.
ASUS provides both 8-pin and 4-pin ATX12V power connectors along the outer edge of the VRM heat sink, located to the right of the CPU socket.