It’s a big speed and bandwidth upgrade
USB4 is purported to be twice as fast as the current USB 3.2 standard (20Gbps), which means it’ll support up to 40Gbps speeds as a maximum in most instances. (Your actual speeds will obviously vary depending on what devices you’re using.)
USB cables use two “lanes” to send and receive signals from connected devices. However, some devices will be able to change a USB4 cable’s to single-direction delivery. For example, DisplayPort 2.0's “Alt mode” will increase the available signal bandwidth to 80Gbps, high enough to support 8K HDR video monitors and other high-speed devices over USB4. The two-lane delivery also means some USB4 devices will support Apple’s Thunderbolt 3 standard, though it’s up to manufacturers on that one.
Speaking of bigger bandwidth allocations, USB4 also supports the USB PD charging standard, which means your smartphones and other devices will be able to charge much faster over USB4—provided they’re built to support fast charging, that is.
USB4 devices can support three maximum speeds: 10Gbps, 20Gbps, and 40Gbps. In other words, make sure you’re scanning a device’s specs to get a sense of its maximum supported speeds if that’s what is most important to you when you’re buying, say, a new laptop (or hub).
And there’s one more speed-related feature that really puts the feather in USB4's cap, as Tom’s Hardware describes:
A big part of the USB 4 spec is the ability to dynamically adjust the amount of resources that are available when you are sending both video and data over the same connection. So, let’s say that you have USB 4 with a 40 Gbps maximum and you’re outputting to a 4K monitor while copying a ton of files from an external SSD. And let’s stipulate that the video feed needs about 12.5 Gbps. In that case, USB 4 would allocate the remaining 27.5 Mbps to your backup drive.
USB4 will be backward compatible
USB4 cables will use Type-C connectors, which is the flat, rounded port found on most smartphones and laptops these days.
You should be able to plug a USB4 cable into just about any USB Type-C port, but it won’t always function the same way. For example, a USB4 cable will experience a drop in speed when plugged into an older port, while older USB Type-C cables plugged in USB4B 4.0 port will use their highest-possible transfer speed by default (but can’t reach the same speeds as a USB4 cable).
Similarly, you may need and an adapter to use USB4 cables with USB Type-A ports, which the kind you usually see on PCs.
Why “USB4?”
According to USB Promoter Group CEO Brad Saunders, the “USB4" branding was chosen to avoid confusion caused by the incremental upgrades of previous USB standards, i.e. “USB 3.1” and “USB 3.2.” It’s also possible that USB4 may be re-branded, or that further upgrades—what would’ve otherwise been “USB 4.1,” for example—will see more definitive naming differences despite still technically being “USB4.”
When will USB4 show up?
The first USB4 cables and devices are expected to arrive around late-2020, but 2021 is probably more likely at this point. Part of this is because USB4 will cost more than older types of USB to manufacture. And we’re kind of in the middle of a global manufacturing shutdown/slowness/Hell, which doesn’t help speed up USB4's launch at all.
Source: https://lifehacker.com/everything-you-need-to-know-about-usb-4-1843246620
