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T420i ExpressCard USB adapter question

T400/T410/T420 and T500/T510/T520 series specific matters only
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hurricanejohn
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Joined: Sat Dec 11, 2004 5:07 am

T420i ExpressCard USB adapter question

#1 Post by hurricanejohn » Fri Oct 16, 2020 4:26 pm

I have a T420i and I am wondering if i get a ExpressCard USB 3.0 adapter if i will actually get those kind of speeds or if I'm wasting my money? I've upgraded the CPU to a i5-2520m if that matters at all

atagunov
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Re: T420i ExpressCard USB adapter question

#2 Post by atagunov » Fri Oct 16, 2020 4:35 pm

Reportedly X220 has got Intel QM67 chipset. Apparently same for T420i.
QM67 is said to feature PCI Express 2.0.
PCI Express 2.0 supports 500Mb/sec per lane.
USB 3.0 is said to support up to 650Mb/sec per port.

I believe ExpressCard connector offers 1 lane of PCI Express. Therefore it seems that while USB 3.0 won't run at maximum theoretically possible speed there's a chance to run close to it. The speed will probably be limited by the ExpressCard itself - and on the devices you plug into it - rather than by Thinkpad.

People have used the same ExpressCard connector on X230 to run an external GPU - and were reasonably happy. They even channeled video back to the internal monitor via the same link: command/textures/etc go out and video goes back via the ExpressCard slot. ExpressCard in a X230 is running on PCI Express 2.0 just like in a T420i. Being able to run external graphics card in my view shows that there is a lot of bandwidth.
X220, 2 *T520

axur-delmeria
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Re: T420i ExpressCard USB adapter question

#3 Post by axur-delmeria » Fri Oct 16, 2020 9:25 pm

Fellow forum member dr_st has a side-by-side comparison of various Expresscard USB 3.0 adapters: viewtopic.php?f=18&t=127819
Daily driver: X220 4291-C91 i7-2620M

Backup: X601 Core 2 Duo T8100
Toy: X60F Core Solo U1300
On loan: X220 4291-P79 i5-2520M
In pieces: two retired but working X61Ts
RIP: 760XD 9546-U9E; X61 7676-A24; and a BOE-Hydis HV121P01-100 in failed SXGA+ mod
:cry:

dr_st
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Re: T420i ExpressCard USB adapter question

#4 Post by dr_st » Sat Oct 17, 2020 2:31 am

atagunov wrote:
Fri Oct 16, 2020 4:35 pm
I believe ExpressCard connector offers 1 lane of PCI Express. Therefore it seems that while USB 3.0 won't run at maximum theoretically possible speed there's a chance to run close to it. The speed will probably be limited by the ExpressCard itself - and on the devices you plug into it - rather than by Thinkpad.
There is no USB device in existence, that is able to run at the maximum theoretical USB speed, and never has been. In PCI-Express the actual speeds of the interface can be quite close to the theoretical, so the interface will not be the bottleneck, but the USB 3.0 chipset will. There are differences and they are quite noticeable in those analyses that I did (which axur-delmeria linked to). However, it is still far better than the onboard USB 2.0.
Thinkpad 25 (20K7), T490 (20N3), Yoga 14 (20FY), T430s (IPS FHD + Classic Keyboard), X220 4291-4BG
X61 7673-V2V, T60 2007-QPG, T42 2373-F7G, X32 (IPS Screen), A31p w/ Ultrabay Numpad, A21m 2628-GXU

TPFanatic
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Re: T420i ExpressCard USB adapter question

#5 Post by TPFanatic » Sun Oct 18, 2020 8:08 pm

The nice thing about T420 is if you want to transfer data across SATA drives you get the built in eSATA port for your convenience.
lenovo T420 i5 2520m 16GB QHD w/ eGPU GTX 960
lenovos T520 i7 2720qm 8GB FHD, T420s i5 3320m 8GB QHD, T430 i5 3320m 8GB FHD, T430 i5 3320m 8GB FHD w/ Optimus, S1 Yoga i7 4600u 8GB FHD
IBM X601 Tablet L7500 8GB SXGA+
Enable 2 finger scroll on old Synaptics touchpads.

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