AMD Zen 4 Ryzen 9 7950X and Ryzen 5 7600X Review: Retaking The High-End
by Ryan Smith & Gavin Bonshor on September 26, 2022 9:00 AM ESTMore I/O For AM5: PCIe 5, Additional PCIe Lanes, & More Displays
AMD’s other big expenditure using socket AM5’s additional pins is on I/O support. While AM4 already supported a fair bit of I/O, including 24 PCIe lanes, 3 displays, and 4 Superspeed USB ports, there was still room for improvement. So for AM5, AMD has increased the amount of I/O and the flexibility offered with the platform.
The biggest change here is that the AM5 socket now provides for 28 lanes of PCIe, a net gain of 4 lanes. More significantly still, PCIe 5.0 is now supported (at least on the Ryzen 7000 “Raphael” processors), doubling the bandwidth of all of those PCIe lanes to a max of 4GB/sec/lane. Which gives the chip a maximum cumulative PCIe bandwidth of 112GB/sec in each direction.
In practice, those additional lanes are intended for NVMe drives, giving AM5 a second x4 connection to drive a second NVMe drive; though we have seen some motherboard designs where vendors are stealing the second x4 for a PCIe 5.0 x4 slot. Past that, things look a lot like AM4, with 16 PCIe lanes to directly drive one or more PCIe slots, and then 4 lanes for hooking up the chipset.
Meanwhile, the updated socket also offers enough pins for the CPU to drive 4 Superspeed USB 3.x ports, and a USB 2 port. The USB 2 port is new for this generation, and meanwhile 3 of those USB 3 ports now also support the USB Type-C connector, unlike AM4 which could only natively drive Type-A ports. As a result, AM5 CPUs can drive a total of 3 Superspeed Type-C ports, a fourth Superspeed Type-A port, and then the aforementioned USB 2 port.
There has been one regression, however, and that is SATA support. Whereas AM4 CPUs could drive a mix of NVMe and SATA drives (up to 2 SATA + a PCIe x2 for NVMe), AM5 is purely PCIe. So there is no native SATA support on the CPU, and supplying that will come from the chipset.
To visualize this, we’ll use part of the AM5 chipset diagram. We’ll go more into the specifics of the chipsets in a bit, but lays out what is wired to the CPU, and what will need to be wired to the chipset. Of note there, the current chipsets only use PCIe 4.0 connectivity to the Ryzen CPU, so the current generation of chipsets will not be making full use of the bandwidth capabilities of the CPU itself.
Which with the addition of PCIe 5.0 support to the platform, is going to be a recurring theme. While AMD has baked in 5.0 support into the Raphael CPUs, it’s up to motherboard vendors to actually make it so. Compared to PCIe 4.0, 5.0 has much tighter signal integrity requirements (the signaling frequency has been doubled), which at least at this time, makes PCIe 5.0 expensive to implement. A very well-designed motherboard is required with impeccable traces, and on top of that the overall short throw of PCIe 5.0 means that retimers/redrivers become necessary rather quickly. So while AM5 can support PCIe 5.0 throughout, the reality is that we’re still going to see a lot of PCIe 4.0 in use even in higher-end motherboards.
As for the necessity of PCIe 5.0 overall, thus far AMD is primarily focused on what it means for NVMe drive speeds. The first generation of PCIe 5.0-enabled consumer SSDs are expected to land a bit later this year, and they should be able to hit sequential burst transfer rates above the limits of PCIe 4.0 (~7GB/sec).
Past that, NVIDIA’s newly announced Ada Lovelace architecture GeForce RTX 40 series video cards do not support PCIe 5.0. So while we’re awaiting AMD to announce their RDNA 3-based product lineup later this year, regardless of what AMD does, the bulk of video cards sold next year are not going to use PCIe 5.0. So there is a bit less pressure on motherboard manufactures (and motherboard buyers) to get boards that support PCIe 5.0 to anything beyond a couple of M.2 slots.
Finally, in conjunction with the USB I/O changes, AM5 also introduces some display I/O changes. Whereas AM4 could directly drive up to 3 displays, AM5 brings this to 4. Specifically, AM5 offers one dedicated display output (which will generally be allocated to HDMI), while the other 3 display outputs are available over those 3 USB Type-C ports as DisplayPort alt mode. It’ll be up to motherboard manufacturers if they want to expose any of these USB-C root ports as physical USB-C ports or as DisplayPorts, but so far from the motherboard designs we’ve seen, the former is more common (though certainly not universal).
Anticipating a shift to more USB Type-C displays, AMD is also implementing what they call “hybrid graphics” support on AM5. Unlike previous products where this referred to linking up the integrated graphics with a discrete GPU in CrossFire mode, this time around it refers to being able to being able to use the mobo/iGPU’s display outputs to drive a monitor while using a dGPU to render content. This is largely lifted from AMD’s laptop technologies, where similar techniques are used to allow the dGPU to be powered down when it’s not in use. In the case of desktop processors, this just means every display output will work, regardless of whether it’s plugged into ports coming from the CPU or a discrete video card.
It’s also worth noting that AM5 is bringing a few other, more minor updates to other comms protocols. Among these is support for MIPI’s (relatively) new I3C chip-to-chip signaling standard, which will ultimately be supplanting the long-used I2C standard. As well, AM5 doubles the number of I2C/I3C ports available, bringing the total to 4 ports. The platform also adds a second (enhanced) Serial Peripheral Interface (eSPI/SPI) port, and on the audio front, adds support for the Digital Mic and MIPI’s Soundwire standard for low-cost audio peripherals.
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tuxRoller - Monday, September 26, 2022 - link
When does an explanation become an excuse?UltraTech79 - Friday, September 30, 2022 - link
Well rehire them or youre going to see a real quality loss. Is it really worth it in the longrun?Ryan Smith - Friday, September 30, 2022 - link
"Is it really worth it in the longrun?"That's a question for the people that pay the bills. It's not my call.
Iketh - Saturday, October 1, 2022 - link
I will professionally edit for next to nothing just because I love this site. Email me iketh28@yahoo.comScottSoapbox - Tuesday, October 4, 2022 - link
Grammarly is a cheap replacement that will catch the worst of it.Sivar - Monday, September 26, 2022 - link
I agree that the paragraph was in need of some work, but "thinkos" happen, esp. with an article of this depth. I like that you reported it, but I wonder if it could have been worded differently. Imagine spending days aggressively writing a detailed analysis, only to have one's writing compared to a stroke victim because of a tiny percent of the article.Jasonovich - Sunday, October 9, 2022 - link
Grammar fascism is distracting from the main body of the article. It's like the cream from your glass of Guinness pouring on to your fingers, no big deal just lick it off. The integrity of the article is intact and I'm sure the message was received loud and clear from Anandtech's spoof readers.Anyway many thanks for the excellent article, other sites don't try half as hard as the folks from Anandtech.
philehidiot - Wednesday, September 28, 2022 - link
This sentence seems perfectly cromulent. I think the point purvulates nicely and is quite unfornitabulated.gryer7421 - Monday, September 26, 2022 - link
Hi, thanks for the article. In the future .. please start posting HIGHEST all-die TEMPS hit during each benchmark..It would be help to know and see the temps for building workstations given that INTEL and AMD both just uncorked the genie by not caring about temps anymore and only caring about ''top cou speed'' at ant (thermal) cost.
Gavin Bonshor - Monday, September 26, 2022 - link
With Zen 4, the highest all-die temp is essentially 95°C, due to the way Precision Boost Overdrive works. The idea is that it will use all over the available power/thermal headroom, so those with better CPU cooling, should technically benefit more.