[Fnoord]

Way before that there was SCSI.

The low cost is price. Asus for example with their ASUS ThunderboltEX 4 allows you to have TB4 via PCIe card.

The neat thing about USB4 was same as PATA and later SATA: widely and relatively cheap available in consumer hardware. SCSI and FireWire were technically superior but were neither cheap nor widely available.

Oh and I don't know about SCSI but FireWire was actually a security risk.

[tga_d]

I know thunderbolt at least up through 3 was generally carte blanche DMA, so an obvious security nightmare (strictly speaking no worse than cold boot attacks and the like, but there's a practicality difference between dumping raw DIMMs and just plugging in a thumb drive -- or inter-machine links like TFA, for that matter). Does TB4 bother trying to solve this?

[p_l]

Not really. Just like with OHCI 1394, it's responsibility of host IOMMU to handle it.

[vegardx]

Just a fair warning about these cards, the support is flakey at best. You should research if it works with your motherboard and CPU before going down that route. I did a lot of research on this because I wanted to connect my Gaming-PC to an Apple Studio Display over optical Thunderbolt, but quickly decided against it.

Luckily there are good alternatives. I landed on a solution using a Belkin[0] DisplayPort and USB to Thunderbolt-cable. I just get USB2.0 speeds, but it's enough for my needs. I'm also able to extend it using an active DisplayPort 1.4 extender, for a total of 10 meters cable.

[0] https://www.belkin.com/support-article/?articleNum=316883