While notebook hardware has steadily improved over the years, outside of the recent MacBook Pro with Retina Display there haven't really been any moves forward in improving desktop real estate in some time. In fact, for productivity-oriented users this continues to be a major reason for sticking with a desktop setup (if not a desktop system): more monitors, more space to work in. This fact of life has resulted in a bit of a niche market in the form of small, USB-powered screens.

We've tested both of GeChic's OnLap monitors and found that while they were flawed in their own ways, they were still able to expand useful work space without incurring too much of an inconvenience in terms of size or power requirements. Yet GeChic's screens need an HDMI or D-SUB port in addition to a USB 2.0 port for power, and if for one reason or another your notebook doesn't offer one of these, you're out of luck. Enter solutions based off of DisplayLink's USB technology, which are able to add another screen driven entirely over USB. Solutions like the screen we have on hand today, Toshiba's catchily-named 14" USB Mobile LCD Monitor. Here's the spec sheet:

Toshiba 14" USB Mobile LCD Monitor Specifications
Model PA3923U-2LC3
Cabinet Color Matte Black
Screen Size 14"
Native Resolution 1366 x 768
Display Colors 256000
Brightness 220 cd/m2 (Claimed)
Contrast Ratio 400:1 (Claimed)
Response Time 16ms
Connectivity USB 2.0
User Controls Power Button, Brightness Up, Brightness Down
Dimensions 13.4" x 9.4" x 0.6" (WxHxD)
(340mm x 239mm x 15.2mm)
Weight 2.8 lbs (1.27kg)
Pricing Online starting at $170

Unlike the GeChic OnLap monitors we've reviewed here and here, which benefited from being driven off of the notebook's GPU, Toshiba's 14" monitor leverages DisplayLink's USB technology (which Jarred outlined here back in 2008). While DisplayLink has USB 3.0-based solutions slowly making their way to market, Toshiba's monitor still uses USB 2.0. Most of the remaining specifications are pretty weak, but this is a laptop designed primarily for office work as opposed to anything that demands color accuracy.

How Does it Work?

As a quick and dirty primer, DisplayLink basically uses on-the-fly compression as needed to stream data over USB to the DisplayLink-enabled monitor. What's important to note is that this means there's no GPU, dedicated or integrated, directly feeding the monitor, and as a result most of the heavy lifting has to be done by the CPU. That also means that gaming is mostly out of the question. Toshiba's monitor wasn't even exposed as an option for any of the games in our notebook testing suite.

I did try to run Duels of the Planeswalkers 2012 windowed and then drag the window over to the Toshiba monitor, and it did seem to be running well, but when I tried to maximize it, both screens were basically caught in a flickering loop. The only way I was able to break the system out of the loop was to shut it down completely.

Nearest I can tell, DisplayLink's technology seems to present itself as a virtual monitor driven by the GPU, and then takes that data and funnels it through the USB connection to the external screen. It's impressive that it works at all, but remember that the funnelling requires on-the-fly CPU-based compression, and you'll see what that means later on.

Setup, by the way, is incredibly easy. While Toshiba includes a driver disc with their monitor, there's a driver readily available for download on Windows Update for Windows 7 as well. Plug the monitor in and let the drivers auto-install, and you're ready to go.

Screen Quality and Performance
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  • repoman27 - Wednesday, June 27, 2012 - link

    Stupid phone, that was meant to be in response to the next comment.
  • lead_org - Wednesday, June 27, 2012 - link

    Okay so that power consumption figure would be different, if you used a different laptop with different CPU/GPU package.

    So you only tested this monitor on a X100e/120e ThinkPad?

    Also, with my ThinkVision LT1421, i can power the entire monitor off a single USB port from the laptop. Can this Toshiba unit do the same?
  • lead_org - Wednesday, June 27, 2012 - link

    How did you arrive with the power consumption figures?

    what you stated sounded a bit high.
  • themossie - Wednesday, June 27, 2012 - link


    For the Toshiba under load: 29.3 watts at 5 volts?
    It's pulling ~6 amps between 2 USB ports?
    Which computer (or common charger, even) lets you pull 3 amps/USB port?

    Even the 20 watts for the GeChic 1301 OnLap is pushing it (would require the laptop to support 2 amps each on 2 USB ports), let alone the 1302...

    Something's very wrong here, Dustin.
  • silverblue - Wednesday, June 27, 2012 - link

    I'm not sure if this has any bearing on things...

    Added to the USB 2.0 and 3.0 specs in December 2010:

    Battery Charging Specification 1.2[12]: Released in December 2010.
    Several changes and increasing limits including allowing 1.5A on charging ports for unconfigured devices, allowing High Speed communication while having a current up to 1.5A and allowing a maximum current of 5A.

    However, from a product review of this screen on the Toshiba website, it states you cannot use maximum brightness without the (optional) AC adaptor. Is this true?
  • themossie - Wednesday, June 27, 2012 - link

    Good catch. I've seen this standard, but not seen it (completely) implemented.
    3 amps is the max I've seen, and that one doesn't use any real standard... just shorts the data pins and calls it a day.

    Can anyone link me to a 5 amp USB charger? Or a desktop/laptop which puts out more than 2 amps/port?
  • Death666Angel - Wednesday, June 27, 2012 - link

    It uses that much power from the wall, not the additional display itself.
    Considering the gap between no USB display and idle USB display, I think it's safe to assume the additional USB display added 6W to the power consumption (increased load being more due to heavier CPU load due to the display branching off the CPU and not the GPU). So your whole 30 Watts at 5V is nonsense. :-)
  • themossie - Wednesday, June 27, 2012 - link

    Completely my bad. I both misread the preceding paragraph and missed the "9 watts with NO USB DISPLAY". All I can offer in defence is that I'm not the only one to do so...

    Back to power - the monitor + extra system load draws an extra 21 watts at the wall, call it 18 watts (~75% efficiency PSU). Subtract 6-10 watts for the monitor, leaving 8-12 watts for increased system load in a test bed with (assuming i7-2637m) a 17 watt TDP CPU?

    I'd like to see CPU load figures while this is running, that's a pretty hefty hit. It's still 3 times the power consumption of a single monitor, which would be pretty detrimental to mobile computing.

    Again I suggest my solution posted a few posts down - which is cheaper, lighter, won't load the CPU or run off of the laptop battery and doesn't need questionable drivers (HDMI input) at the cost of 2.5" less screen size.
  • Dustin Sklavos - Thursday, June 28, 2012 - link

    CPU load runs between 10% and 40% on the 17W i7.
  • lead_org - Wednesday, June 27, 2012 - link

    You do know how much power a standard USB 2.0 can put out right?

    For comparison purpose a Lenovo ThinkVision LT1421 can draw a maximum of 5 watts under full load.

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