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Comment by dont__panic | Hacker News Reader

> Jeff Ravencraft, president and COO of USB-IF, told Ars that USB4's multi-monitor support depends on the computer "and is a question of how many streams a host can support, but "from a bandwidth perspective, the maximum is four 1K monitors at [a refresh rate of] 120 Hz, two 4K monitors at 120 Hz, and one 8K monitor at 30 Hz."

Two 4k monitors at 120hz? Does anyone have experience getting that kind of resolution + refresh rate over a single TB4 cable? According to the bandwidth calculator I use, it is less than 40Gbps, but I guess color bitrate can bump it over if you're using an HDR monitor.

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Hm interesting that the quoted text argues in terms of bandwidth. A 4K resolution has 16x as many pixels as a 1K resolution. So if you can run two 4K monitors then shouldn't the bandwidth allow you to run 32 1k monitors at equal Hz? Same for the 2x 4K at 120Hz vs 8K at 30Hz. 8K is four times the pixels than 4K. At a fourth of the refresh rate, shouldn't it be also two 8K monitors? I am not very knowledgable when it comes to display protocols.

I guess with "1K" they mean 1080p, because then it'd suddenly make sense. I'd be really curious who made the mistake of calling it "1K".

"1K" must be a typo; it would refer to the legacy XGA resolution of 1024x768.

"2K" has its origins in digital cinema (where it actually was 2000 pixels wide), but it has since become used interchangeably with 1080p (1920px wide) alongside "4K" becoming the common term for 2160p (3840px wide).

(Further confusing things, I've also seen some usage of "2K" to indicate 1440p, although it would be more accurately termed "2.5K".)

Unfortunately the marketplace has pretty much standardize on 2K being 1440p (see links below)

https://www.newegg.com/p/pl?d=2K+monitor

https://www.amazon.ca/s?k=2k+monitor&sprefix=2k+mo%2Caps%2C8...

https://www.microcenter.com/search/search_results.aspx?N=&ca...

https://www.benq.com/en-ca/monitor/gaming/ex2780q.html

https://www.viewsonic.com/us/vg2756-2k-27-1440p-ergonomic-ip...

I think I have a decent understanding of the bandwith provided by various TB/USB standards, but this article was all over the place and actually made me doubt the information I've researched in the past for my home desk setup.

And this article somehow misses the most interesting aspect of the USB 4.0 Version 2 announcement: retroactive bandwidth upgrades to existing cables. (https://www.theverge.com/2022/9/1/23332838/usb-4-version-2-8...)

That might just be a misunderstanding as well, though. I get the impression that the USB folks aren't very discerning about their terminology in press releases. They could really use an editor to avoid this kind of confusion.

> And this article somehow misses the most interesting aspect of the USB 4.0 Version 2 announcement: retroactive bandwidth upgrades to existing cables.

This is noted in the “USB4 Version 2.0” section.

“…it's supposed to enable up to 80Gbps over USB-C through a new physical layer architecture that uses ‘newly defined’, as the USB Promoter Group put it, 80Gbps USB-C active cables and the 40Gbps USB-C passive cables that already exist today.”

Nice catch. I feel like this deserves way more discussion, though -- how are they doubling the throughput of existing cables?!?! I wonder if software updates could also upgrade existing USB4 interfaces, too.

> I feel like this deserves way more discussion, though -- how are they doubling the throughput of existing cables?!?!

Going back to the press release¹, I'm wondering how much weight "up to" carries. That is, I'm guessing that reliable 80 Gbps operation will require new, active USB-C cables, even though existing cables may realize some benefit.

"Up to 80 Gbps operation, based on a new physical layer architecture, using existing 40 Gbps USB Type-C passive cables and newly-defined 80 Gbps USB Type-C active cables."

¹ https://www.businesswire.com/news/home/20220901005211/en/USB...

Probably the encode/decode ASIC can be upgraded due to process improvements (this is why wifi an ethernet improvements see such steady improvements - Moore's Law). Drivers and firmware probably improve incrementally as well.

Since when has the "K" designation referred to the vertical? 2K = 2048 horizontal. 4k = 4096 horizontal.

I have personally never seen 1080p referred to as 1K

I honestly don't know why people bother with the "K" names and the "UHD", "QHD", etc. No two people seem to agree exactly what they all mean.

It's far easier to just use the the numeric resolution, "1920x1080", "3840x2160", etc.

Because marketing.

FHD has about 4x the amount of pixels than 1K. They'd be still off by a factor of two (32/4 = 8 vs 4).

The problem is that 2K is already taken. So we have

1K --> FHD (1920x1080)

2K --> QHD (2560x1440)

4K --> UHD (3840×2160

Isn't the K relating to the horizontal axis? 1K being close to FHD doesn't seem to make sense.

  1K (1024x540) ~= qHD (960x540)
  2K (2048x1080) ~= FHD (1920x1080)
  4K (4096x2160) ~= UHD (3840x2160)
  8K (8192x4320) ~= QUHD (7680x4320)

Vertical axis is the same, just different aspect ratio and horizontal axis.

That's the theory, but in the market place right now we have:

2K --> QHD (2560x1440)

4K --> UHD (3840x2160)

Check out Amazon, NewEgg, BestBuy, etc. That's the current market convention naming.

https://www.newegg.com/p/pl?d=2K+monitor

https://www.amazon.ca/s?k=2k+monitor&sprefix=2k+mo%2Caps%2C8...

> QHD (2560x1440)

That should be 2.5K or something if they want to downscale that silly naming system. 2K means 1920x1080.

Should, but in the market place its called 2K. Check Amazon, BestBuy, NewEgg, etc.

The marketplace terms are now like:

Full HD --> 1920x1080

2K --> 2560x1440

4K --> 3840x20160

https://www.newegg.com/p/pl?d=2K+monitor

https://www.amazon.ca/s?k=2k+monitor&sprefix=2k+mo%2Caps%2C8...

That's messed up. Both sites' filters even call 1080p "2K", but most manufacturers are using the term for 1440p.

I don't think they call 1920x1080 2K, I think they call 2560x1080 2K which is a odd resolution as well.

Two monitors 3840x2160 at 30bpp (10bit HDR) at 120Hz is about 33Gbps so that can fit in 40Gbps USB4 supports. With Display Stream Compression 8k60 is probably doable.

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