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Asus Prime X399-A Motherboard Review

While the PC worlds’ attention was on on the resurgent AMD and the release of Ryzen, the tease of the X399 platform and Threadripper CPU’s was in the back of enthusiasts minds. Here we are. Finally AMD is right back into the thick of a market it has been noncompetitive in for over a decade, the high end desktop. This means we have new high end feature packed motherboards to drool over. The first of which we have on hand here today, The Asus Prime X399-A.

Threadripper and the X399 Platform Overview

Before we get into the Prime X399-A, lets have a X399 platform and CPU refresher. Back in March, we declared that AMD was back as a serious competitor in the x86 CPU market. Around that time we started to get whispers of something else, something crazy.. And so the rumors of the X399 platform began, accompanied by unprecedented desktop core counts. Forget the puny 10 core 6950X, Threadripper promised a 16 core/32 thread monster. Take that Intel!

Desktop CPUs have relatively low core counts and small die sizes, so they are easier to design and manufacture. As the number of cores goes up, so does the complexity, whilst yields go down. This isn’t so much of a problem when you’re charging many thousands per CPU, but when viewed through the desktop prism, there really is a limit to how much you can pack onto one monolithic die before running into issues or diminishing yields and returns.

Modularity was a key consideration and lies right at the heart of the AMD EPYC and Threadripper design. From the outset, AMD designed Ryzen to have basic building blocks able to be joined together to create higher core count models. AMD calls this building block ‘Zeppelin’ and it is this block makes up the desktop Ryzen series. Join two together like we have with the 1950X, and we have up to 16c/32t when fully enabled. AMD have high end server EPYC models with up to four of these dies linked together with what AMD calls ‘Infinity Fabric’, making a 32 core/64 thread CPU. This means AMD could relatively easily release 24 or 32 core Threadripper CPU in the future if they chose to do so.

At $999 USD, the Ryzen Threadripper leads the range with its amazing 16 cores and 32 threads. It is joined by the 12C/24T 1920X and the 8C/16T 1900X. These prices are very strategically set by AMD in order to offer superior core counts relative to the Intel opposition. Like the rich kid in the schoolyard, Intel just had to one up AMD with the ‘mine is better than yours’ i9-7980 XE. Whilst this will no doubt be a super sexy CPU, there is little doubt it is a product brought about by the competition. Intel does not do altruism. Competition is good,  we love it, and so should you. Bring it on!

All of this means that desktop users now have access to high core counts that were previously restricted to the enterprise realm. Anyone doing serious content creation will marvel at the parallelism on offer, particularly with modern codecs able to make use of as many threads as you can realistically throw at them. Multitasking will be laughed off. You can game, stream and record all at the same time, you can render faster than ever, run complex data sets faster, run virtual machines and anything else that can make use of serious multi threading.

Note that this series isn’t really aimed at gamers. Even AMD themselves make this point. Gamers will likely see no benefit at all from the likes of a Ryzen 1700 or 1800x. Software developers are somewhat restricted too. They need to make their games playable with dual and quad cores that make up the vast majority of gamers machines, and probably will do for several years to come.

Have a good look at this block diagram. AMD is offering the full complement of 64 PCIe lanes across the entire range. Having 64 lanes to allocate means that a board like the Prime X399-A doesn’t have to compromise when it comes to multiple GPU’s, multiple M.2 drives and dedicated expansion cards. This is a big plus for AMD over X299. This is what the HEDT is all about: running high end systems with all the trimmings without having to compromise.

Unboxing and Overview

Despite not being a high end motherboard (relative to X399 standards) the board is still chock full of tasty features. Its good to see a box that focuses on the product itself, rather than have dragons or snarling beasts or warriors with lasers. You don’t see Apple or Samsung resorting to that. This is a product aimed at the serious, discerning end of the market.

And there’s a rundown of said features on the back of the box.

Below you can see the key specifications of the board. You can find the full specifications here

As something of an entry level board for the X399 platform, there aren’t any expensive over the top features. A notable omission is WiFi, which we think should be an option on a board of this price.

Moving onto the included accessories, we have a decent, if not fully comprehensive list for a board of this price. First up we have four SATA cables, a M.2 vertical bracket/holder and accompanying screws. This is for use with the M.2 slot that sits at the right of the motherboard. Then we have a SLI bridge for two way setups. This bridge is a HB version that supports the 650Mhz SLI interface for Nvidia Pascal GPU’s. It is recommended for high resolutions.

Then we have the manual, I/O plate, front case EZ connector, driver disc and a code for a discount off the purchase price for CableMod accessories.



Here’s the board itself. Motherboard manufacturers aren’t differing too much with their layout these days and the Prime X399-A looks pretty good at first glance. You may notice the grouping of the 24 pin, 8 pin and 4 pin power connectors. this could be a nice way to manage cable routing. Do note that its a Extended ATX board, so you will need to pay attention to that.

The board looks nice. It suggests functionality over excessive bling, though even this board isn’t immune to the RGB craze. The chipset heatsink has a set of RGB lights. These are controlled by the AURA SYNC software.

Part of the main chipset heatsink doubles as a heatsink for a M.2 drive. It blends in quite nicely to the board. On an semi related note, its a shame that we are seeing this kind of thing with M.2 drives. They should not require cooling like this. If the U.2 form factor was more widely adopted, this would eliminate that problem, but that’s a story for another day.

We have a standard set of SATA ports, plus a U.2 port which are not included on many X399 and X299 motherboards. Its good to have the option though, as the CPU has plenty of PCIe lanes to accommodate it if required.

Of course there’s a USB 3.0 header here too.

As you can see below, its interesting to see the EPS power connectors grouped right next to the 24 pin ATX power connector, this is somewhat unusual, but might be of interest to those who like a really clean looking system.

We also see the vertical M.2 slot, which can be used in conjunction with the bundled M.2 drive holder. Also on the left is a newer generation front panel USB 3.1 header. We think this header will become more and more common on cases as we move into the future.

Below we see the PCIe slots. The board is designed for two or three way use, with four way not supported and the layout reflects this. The number of PCIe lanes is where the Threadripper platform really wins.  All four 16x slots are wired directly to the CPU, though only three of the full-length slots are equipped with metal reinforcement guards. These slots are x16/x8/x16/x8 electrically. When using a two or three card system, you’ll have x16/x16 or x16/x16/x8 respectively.

Note there are a pair of PCIe 2.0 slots wired from the chipset. These are the X1 and x4 slots.

The bottom of the board is chock full of headers. From left to right we have the front panel audio header, debug LED, power on/off (but no reset button), RGB header, two chassis fans, an external fan header for other Asus products, two USB 2.0 headers, a USB 3.0 header, a water pump header (with higher power capability), m.2 fan header, clear CMOS header and finally the front panel connector, Phew!

The PWM is an eight-phase design, don’t let this fool you into thinking this is inferior to some 46285 l33t phase solution though. These are top quality components that are easily capable of powering an overclocked 16 core Threadripper. It is not dissimilar to the PWM found on the ROG Zenith. The MOSFETs are cooled by a metal heatsink connected by a heatpipe to a secondary heatsink located adjacent to the rear I/O. This has a small 40mm fan, which is pretty rare on 2017 motherboards, however on a motherboard that can pull some serious amps, this is good to have. In our testing, we couldn’t hear it over the sound of the other system fans and components.


Finally we have a look at the rear I/O, which seems a bit bare really. That space to the left of the USB ports is just crying to have a Wifi/Bluetooth module.

From left to right we have a clear CMOS button, and eight USB 3.0 ports which are controlled by the chipset. The LAN is powered by an Intel I211-AT chip, which is known for its reliability, compatibility and low CPU overhead. It’s a good choice.

Then we have USB 3.1 Type-A and Type-C ports which are controlled by a ASMedia 3142 chip.

Finally we have the audio with analogue and S/PDIF ports. These are powered bu a standard Realtek ALC1220 codec with software control by Asus’ Crystal Sound 3 suite. Of course Asus has equipped the Prime X399-A with EMI shielding, electrolytic capacitors, PCB isolation and some additional circuitry to protect the signal as much as possible. 2017 audio has come a long way, with the 120Db S/N ratio of the base codec being a good place to start. The ALC1220 it is greatly improved over older ALC codecs which were really lacking in performance and spec, no matter how much you tried to polish them.

BIOS Overview

The UEFI of the Prime X399-A is very similar to the X299 TUF Mark 1 we reviewed recently. As we noted then, Asus have a consistent reliable record of successful BIOS implementations and they haven’t made many changes over the last couple of years. We think that Asus BIOS’ have a steeper learning curve compared to the likes of MSI, though that is lessened somewhat with the smaller number of parameters offered by the X399 platform. Not that it’s lacking though. Unless you are part of the 1% of the 1% of overclockers, you will have no problem finding the feature you want quickly.  The colors, fonts and contrasts are easy on the eye and many settings have accompanying descriptions which makes things a hell of a lot easier for a less technically adept user.

In addition to the default EZ mode that we see in the screenshot below, there are 8 main pages, most of which have their own subsections. Asus have placed the commonly accessed first boot up settings on the EZ mode page. These are the ones you would typically set and forget upon powering up the system for the first time. Cooling functions, RAM & XMP setting and boot configuration are here. If you want to access the more advanced settings, you will press F7 to take you to the main BIOS.

The default screen that is seen when entering the advanced section of the BIOS is called the ‘My Favorites’ tab. As the name suggests, the settings you access most are displayed here for easier access.

Below is the ‘Main’ page. Here is where you can see basic system information.

Here we have the ‘AI Tweaker’ menu. This is the major overclocking settings page. Despite not being a OC oriented platform or motherboard compared to the ROG series, almost every realistic option is still included. You’ll run into thermal limitations well before the board hits the wall unless you are using exotic cooling.

Below is the ‘Advanced’ page. Most of these settings relate to the onboard devices and peripherals. including the USB, storage, networking and a whole lot more.

The ‘Monitor’ tab is where you will find real time reporting of voltages, temperatures and fan speeds. Quite a lot of these can be configured, for example, a warning when a temperature goes above a desired level.

The ‘Boot’ tab is fairly self explanatory. The boot order, overrides and startup settings are found here.

Next up is the ‘Tools’ tab. Here you can set OC profiles and update the UEFI. Note that the graphics card information selection only shows the information of ASUS graphics cards.

Finally there is the ‘Exit’ menu.

Software Overview

Asus continues to update their very good AISuite software. there’s a full range of monitoring, overclocking, fan control and power saving options available, all with the traditionally intuitive and nice looking interface.

The Asus RGB control software is simply called Aura Sync. The lighting on the Prime x399-A is limited but it still functions well and has a very good range of effects. We particularly like the Starry Night effect, where the lights would periodically flash bright. Cool!

Test Setup and Benchmarks

Our test setup configuration can be seen below. Comparing different CPU’s and platforms can get a bit tricky. For our CPU test platforms, we try to keep things on a level playing field with relatively low memory settings and all CPU parameters set to default, including all turbo modes in order to best reflect out of the box performance. We just got another X399 motherboard in, so we’ll be adding the results from that board next time.

Lets start of with Cinebench. It supports up to 256 threads, so it will be a standard test of ours for some time to come. Cinebench really shows the strength of Threadripper. Just look at that multithreaded score! If your main task is content creation, a board like the Prime X399-A will serve you very well and add oodles of multithreaded performance goodness.

SuperPi is still a darling of the OC community despite its age. It doesn’t have too much relevance to day to day performance, but it is still a good indicator of single thread performance. The Intel CPUs are much faster here.

File compression is an application that makes significant use of available memory performance and tends to scale well with more cores. AMD is very strong here, obliterating everything in sight, at least until the higher core count Intel CPU’s make their appearance. The R7 1800X is also strong despite losing out with its dual channel vs quad.

Threadripper was made for video work. One of the prime reasons for owning a PC in 2017 is video capability. Smartphones and tablets will just never cut it. It’s the era of 4K, Netflix and millions of twitch streamers and youtubers all relying heavily on compute capability for video encoding and decoding. In this bench we think there could be something here that’s preventing the 1950X from really pulling away further. perhaps the software isn’t quite optimized. More testing is needed.

This is more where we’d expect to be, with almost linear increases in performance with increasing core counts. What a massacre!

This kind of result bodes well for intensive graphics with lots of particles and objects being rendered.

Now for a couple of gaming tests, starting off with Shadow Of Mordor. At 1080p our results are still in line with what we’ve been seeing from other Ryzen processors. Threadripper really isn’t a gaming chip but it’s good enough. Are you really going to notice 140fps vs 160? Purist competitive gamers with their high refresh rate monitors will will say yes, but in any graphics limited scenario, the results will come right back to the GPU. Gaming isn’t everything, though if you are a streamer or multitasking, using it for work and play then you will be pleased with Threadripper and the Prime X399-A, with plenty of performance on hand.

As we can see here when we move to 4K, once the graphics become the limiting factor, the CPU becomes much less relevant. So while there have been some headlines criticizing 1080p gaming performance, its really a non issue once you move to a powerful GPU and higher settings.

To measure power consumption we use software to look at the various package parameters and states. Idle power consumption sits around 40-45w, which is a LOT, but remember we are dealing with a 16 core CPU. Still, we’d like to see it lower than this. Under full load, the CPU is around 175 to 180w, which is bang on what AMD says they will use. We’ll have a look at how power consumption goes other X399 motherboards.

Below is a quick and dirty OC. 16 cores at 4Ghz+ Sweet! Also setting DDR4-3200 was very easy, despite the tested BIOS being the 1st release! This is very good to see from the Asus Prime X399-A. Usually new platforms take some time to mature, so to get this from the first release is a very good sign and says a lot about the work Asus put in to be ready from day one. We’re quite sure that memory performance and support will improve over time. This is a very good start though. DDR4-3200 is a good sweet spot for performance/price.


Threadripper really kicks butt.. provided you can make use of it.. For some users, it doesn’t make any sense at all, but for others, it is simply magnificent. You’ll know which category you fall in. X399 is not a cheap platform. Motherboards like the Asus Prime X399-A are complex and there are no cheap X399 boards, but the Prime X399-A is what we would call relatively cheap at $585. $585 you say? well, compared to some others, it really is affordable (all relative of course)

The Asus Prime X399-A covers what we’d consider to be the basics for this platform. That doesn’t mean its feature light, far from it, but some of the really high end models have things like WiFi, 4 way GPU support, more USB 3.1 etc, though those features are probably secondary to what people are buying this platform for. It still ticks all the key boxes and will serve you well doing the tasks you are buying into this platform for, which is the incredible CPU power on tap. If you want RGB, and all the bells and whistles, do check out the ROG Zenith. That thing is otherworldly, but be prepared to pay hundreds of dollars more for it.

AMD squarely positions Threadripper for content creators and multi tasking. It really isn’t a gaming oriented CPU, though it will serve you well if you are gaming, streaming, downloading a torrent, having a Skype chat and about a million other things at the same time. If you’re this sort of user, then you will adore Threadripper and the 1950X paired with the Prime X399-A. If you’re more interested in pure gaming, Then a Kaby Lake or Ryzen CPU will serve you well. Single threaded performance still matters, and Intel is still ahead there.

A motherboard like this is easy to recommend if you need the power it offers. There are users that will love it. It brings all the performance of the X399 platform and all the goodies it brings, along with those 64 PCIe lanes for the best available expansion capabilities. Though the Asus Prime X399-A isn’t cheap at $585 SGD, relative to some X399 boards, its a bargain. For the money you get a solid reliable motherboard with Asus’ quality BIOS and support. The early BIOS is very good already, pointing at a very good underlying design. It will allow Threadripper to shine and we’re sure will get even better over the coming months as BIOS continue to roll out, something we know Asus will do.



OC capabilities

Traditionally solid Asus BIOS

M.2 cooling design

Lots of fan headers

Somewhat subtle design


No Wifi/Bluetooth

This is not a cheap platform

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