102 PCWorld DECEMBER 2019FEATURE HDMI VS. DISPLAYPORT
HDMI and DisplayPort are similar when it
comes to practical applications, and the
industry largely views them as complimentary
standards. Indeed, HDMI 2.1 offers VESA’s
Display Stream Compression. DisplayPort’s
raw specs are certainly more impressive, but
HDMI’s capabilities have always been more
than adequate for the mainstream A/V market.
Note that both standards can drive older
display types, both via adapters and adapter
cables: HDMI to VGA and DVI; and DisplayPort
to VGA, DVI, and HDMI. Both standards are
also backward-compatible, falling back to the
oldest revision used in a connection.
On the next page is a chart showing major
features and specs for each standard.
HDMI and DisplayPort do the same
things, but in very different ways, and there
are features unique to each. HDMI explicitly
supports CEC (Consumer Electronics Control)
for controlling entire A/V setups, and an
HDMI cable can carry ethernet information.
Ethernet requires a purpose-built cable as
described in Cables section below.
DisplayPort supports CEC over an auxiliary
channel, but it’s rarely if ever implemented,
due simply to DisplayPort’s faint footprint in
the consumer electronics world.USING MULTIPLE DISPLAYS
ON HDMI AND
DISPLAYPORT
Probably the biggest practical difference
between the two standards is that DisplayPortcan drive four daisy-chained displays and
HDMI can drive just two, with
implementations of the latter being extremely
scarce.
Note that the 48Gbps per second and the
80Gbps quoted above are the raw HDMI 2.1
and DisplayPort delivery speeds, respectively.
DisplayPort 2.0 has four lanes that can deliver
approximately 77.37Gbps (19.34Gbps per
lane) of actual data, while DisplayPort 1.4a can
deliver 32.4Gbps (6.48Gbps per lane);
HDMI 2.0 delivers 14.4Gbps; and the older
HDMI 2.1 offers 42.6Gbps.
To determine if a resolution will work, use
the following calculation and compare it to
the available bandwidth: Horizontal
resolution × vertical resolution × bits per pixel
(i.e., color depth) × frames per second. For
example: 3840 × 2160 (4K UHD resolution) ×
24bpp (8-bit color depth) × 60fps (refresh
rate).
Divide the standard’s total data rate by
your result to see how many displays you can
use at that resolution with DisplayPort. There’s
a handy calculator at KV Audio (go.pcworld.
com/kvad), although it misidentifies bits per
cell (sub-pixel) as bits per pixel in the color
depth field (8bpc = 24bpp, etc.). Just to give
you an idea, DisplayPort 1.4a and 2.0 can
drive four daisychained 4K UHD displays with
8-bit color depth and a 60Hz refresh rate.
You’ll need the newer standard for 10-bit
(30bpp) color—or use DSC [Display Stream
Compression; go.pcworld.com/dscm]).