First, in September, the USB Implementors’ Forum (USB-IF) said that it was going to double the throughput of USB4 while using the same copper cables – no mean feat – but didn’t say how it was going to do it (USB Promoter Group Announces USB4® Version 2.0). Now it has revealed the key change that it is making and more about this important change (USB-IF Announces Publication of New USB4® Specification to Enable USB 80Gbps Performance). VESA, at around the same time, announced DisplayPort 2.1 which helps with the integration with USB4. Not to be outdone, Intel gave some clues about Thunderbolt 5 which will go the same way. VESA Releases DisplayPort 2.1 Specification)
If that wasn’t enough, last week AMD announced its latest AIBs and GPUs, the RX7900 series, and said that it would support up to 8K 165Hz or UltraHD at up to 480Hz using DisplayPort 2.1. In the video, Samsung teased a new 32:9 (we think) 7680 x 2160 (we think) monitor that will be officially launched at CES along with new 8K monitors from a number of makers. That’s a lot to digest, but it really moves things along, especially for 8K.
USB4
First, what magic has USB-IF conjured from its existing copper cables to double the throughput? The key change in USB Version 2 is a move from two values per clock pulse (i.e. +1/-1 or 1/0) to three values (+1/0/-1) which allows you to send up to 8 values in every two clock cycles instead of just 4. This is a form of Pulse Amplitude Modulation (PAM) and the specific scheme it uses is Pam-3 which is already used in some other interfaces including some ethernet.
Pam-3 encoding squeezes more bits from the same number of clock cycles
The use of this technology doubles the data that can be transmitted and can use the same copper as the first USB, although new transmitters and receivers will be needed, so products are not likely to be around until the end of 2023 or early 2024 – my guess is that the big push will be at CES 2024. The technology means that the existing four lanes of communication are each doubled from 20Gbps to 40Gbps which means that in bidirectional mode, the interface will support 80Gbps each way.
However, for displays, there is an additional mode, where three of the four lanes can be used for display output and one used for returning data. That will give 120Gbps one way and 40Gbps back – and that’s enough to support 8K120P or dual 8K60P displays even without any DisplayStream Compression and with 4:4:4 graphics data.
USB has also developed a standard for active cables, but that’s a topic for another day.
DisplayPort 2.1
VESA is also updating DisplayPort to V2.1 to tighten it up to work better with USB-Type C and USB4 and it will now use the same physical interface as USB4. It will also mandate the use of DisplayStream Compression (DSC) as well as the Panel Replay specification (which allows the display to keep a frame store and only sends the changing pixels over the interface). That’s a big deal for multiple displays, high resolution and high refresh systems.
Mandating DSC support is a big deal in helping to deliver higher resolutions and frame rates, in my view. Although. in general, compression schemes, including this one, are ‘lossy’, I have seen enough demos of DSC to be convinced that you really cannot see any artefacts and that DSC is genuinely ‘visually lossless’.
Thunderbolt 5
Intel has also said that it will, of course, update Thunderbolt to version 5. Details have not been made public, yet, but the firm has said that Thunderbolt 5 will support the bidirectional 80Gbps and the optional 120Gbps/40Gbps scheme. That will allow host systems (such as forthcoming Apple Macs which are expected to have Thunderbolt 5 support) to support multiple 8K displays.
(readers may remember that USB4 was developed from Thunderbolt technology that Intel made available)
AMD Ups the Ante for Gaming Displays
AMD launched its RX7900 GPUs and cards and really emphasised its support for DisplayPort 2.1 which will support up to 900Hz in 1440P, 480Hz in UltraHD and 120Hz in 8K. New monitors that will support DisplayPort 2.1 will be available from Dell, Samsung, Asus, LG and Acer, AMD said. Performance depends on the game as well, but AMD said that Dawn of Ragnarok (Assasins Creed) will run at 96fps in 8K.
AMD said that the 4K performance will be fast enough for professional eSports gaming, allowing the use of better displays.
All of this news gives a big boost to the possibility for 8K in the PC space and, presumably, later in the console arena. I’m among those that thinks that higher frame rates are even more important in 8K than in lower resolutions and widespread support for 120Hz is really going to be a significant change for the future.
The other thing that made me think about this announcement is “What about HDMI?”. I remember, years ago, the USB-IF in one of my regular CES meetings, telling me that USB had the aim of being the ‘only interface for everything’. It seems to me that USB is getting a long way towards this with the mandating of USB Type-C on any volume smartphones (thanks, EU), the development of USB PD* to power devices and now with this high end display support.
Of course, there is a huge installed base of HDMI, but the idea of replacing HDMI with USB doesn’t seem crazy to me. (BR)
