Resolved USB 3 device in USB 2 device not running at full speed?

[poiihy]

I have USB 3 external hard disk. When connected to a Mac with USB 3 port, the hard disk runs at speeds ~100MB/s of Read and Write. But on my older MBP with only USB 2 ports, it only runs at ~30MB/s R/W. The Maximum speed of USB 2 is 60MB/s, so why is it running only half?

 

[ColdCase]

USB3 is by directional, USB2 is simplex... USB3 protocol is more efficient when storage handling data.... bunch of things including the old MBP hardware.

 

[poiihy]

USB3 is by directional, USB2 is simplex... USB3 protocol is more efficient when storage handling data.... bunch of things including the old MBP hardware.

USB 3 device connected to USB 2 host should run the same as a USB 2 device connected to USB 2 host.

I'm just wondering why it runs at only half the maximum speed.

 

[takeshi74]

I'm just wondering why it runs at only half the maximum speed.

Your answer lies in the comment above that USB3 is full duplex (referred to as bidirectional above) while USB2 is not. It is running full speed.

 

[poiihy]

Your answer lies in the comment above that USB3 is full duplex (referred to as bidirectional above) while USB2 is not. It is running full speed.

You mean USB 3 devices are full duplex and USB 2 devices are not, so native USB 2.0 devices will be able to run at 60MB/s but native USB 3.0 devices won't?!

I thought USB 3 has the same connectors as USB 2, just an extra 5 pins. SHouldn't it function exactly like a USB 2 device when used as a USB 2 device?

 

[waw74]

that's about what i expect from a USB2 drive.
the 60 is the "theoretical maximum"


link

Typical hi-speed USB hard drives can be written to at rates around 25–30 MB/s, and read from at rates of 30–42 MB/s,

"at least 10 to 15 percent of the stated peak 60 MB/s (480 Mbit/s) of Hi-Speed USB goes to overhead — the communication protocol between the card and the peripheral. Overhead is a component of all connectivity standards."

 

[matreya]

Jesus, it's like trying to program a potato to do aerobics...

Just accept that USB2 drives (and USB3 drives that are operating on a USB2 bus) will never exceed 30MB/sec

The fact is your Mac is old and out of date

 

[ColdCase]

USB 3 device connected to USB 2 host should run the same as a USB 2 device connected to USB 2 host.

I'm just wondering why it runs at only half the maximum speed.

You have a USB2 drive that operates at 60MBPs?