SEPTEMBER 2020 PCWorld 83WHY NOT UHS-III?
If you’re wondering why we’re not using an
even faster SD card using the newer
UHS-III bus, it’s because we couldn’t find a
card that even supported the newer
interface, which takes speeds to 312MBps
in full duplex mode and 624MBps in
half-duplex mode. Having searched
Amazon.com, we saw no signs of a UHS-III
card for sale.
(And no, don’t confuse UHS-III [the bus]
with the U3 symbol. U3 refers to the card’s
“UHS Speed Class” mark for video
performance of a camera and card. Yes, they
seriously have U3 and UHS-III which don’t
mean the same thing. U3 has largely been
supplanted by the newer and slightly less
confusing “V” video speed class mark.)
We contacted SanDisk to ask why it wasn’t
offering a newer UHS-III bus card. Company
officials said it’s largely concentrating on the
even faster SD Express standard (go.pcworld.
com/sdxp), which has a speed limit of
3,940MBps.
LAPTOP SD CARD SLOT
PERFORMANCE
All four laptops feature integrated card
readers, but performance varied greatly, as
you can see from our first test, Crystal Disk
Mark’s default sequential read test. The
Dell XPS 15 9500 comes out in front by a
fair margin over the XPG Xenia 15 and Dell
G5 15 SE, but it’s very close to the
Gigabyte Aero 17.
Aero 17 and XPS 15 9500 users can be
happy they’re getting awesome read
performance, but you’re probably wondering
just why the Xenia 15 and G5 SE 15 are
sucking wind. You’ll see the reason if you look
at the labels for the laptops above: It’s largely
due to the card reader and the interface
they’re connected to.
For the worst laptop here, the Dell G5 15
SE, it’s likely gated by the USB 2.0 interface
it’s hooked up. USB 2.0 has a maximum
theoretical speed of 480Mbps or 60MBps.
Once you account for overhead it’s generally
far lower than 60MBps.
After the Dell, the XPG Xenia 15 doubles
the performance of the G5 15 SE with about
91MBps read speeds. The Xenia 15 highlights
the other issue that matters for a laptop’s SD
card reader: It’s not just the interface, it’s also
what the host card reader is rated for.Dell XPS 15 9500UHS-III x1 PCIeGigabyte Aero 17UHS-III USB 3.0SanDisk ExtremPro e
UHS-III Reader USB 3.0
XPG Xenia 15USB 3.0Dell G5 SE 15USB 2.0CrystalDiskMark 7 Seq.
Read (MBps)LONGER BARS INDICATE BETTER PERFORMANCE2792462629140