How long is the cable, and what type of connectors does it use?

The cable is 6 ft long and uses male-to-male connectors, with a latching DisplayPort connector on one end and a gripping HDMI connector on the other.

Can this cable output 4K video at 60Hz from a DisplayPort 1.4 source to an HDMI 2.0b display?

Yes. This StarTech active DisplayPort-to-HDMI cable supports 4K at 60Hz and is designed to connect from DisplayPort 1.4 to HDMI 2.0b.

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StarTech 6ft DisplayPort to HDMI Cable - 4K 60Hz Active DP 1.4 to HDMI 2.0b Video Adapter with Gripping Connector Model 6F-DP-HDMI-4K60-GR