qubit <
qu...@quandoveloce.com> wrote:
> just for the record, A MacBook Pro at this time, does not run three 27
> inch Thunderbolt displays concurrently.
That's not surprising. The graphics controller only supports two
external displays using Mini DisplayPort or Thunderbolt. You have to use
the HDMI connector for a third display.
> Had the MBP delivered 2 days ago, and connected 2 TB displays ( one DOA;
> it happens, no biggie). Took the opportunity on phone to Apple to ask if
> it would run a third TB display via HDMI, so I could have an extended
> desktop; after some referral, answer is yes, so I ordered a third, A
> replacement for the DOA arrived today, and the new third display.
I don't understand how someone at Apple could have answered yes to that
question as it is clearly impossible with currently available products.
An Apple Thunderbolt display can only accept a display signal from
Thunderbolt, not from HDMI.
As far as I know, there are no adapters which convert an HDMI output to
Thunderbolt.
There are adapters which convert from HDMI to DisplayPort (or Mini
DisplayPort), e.g. this one from Belfan:
http://www.belfan.com/products_detail_D.asp?id=1790
Note that it is a box with a separate power supply - converting from
HDMI to DisplayPort is relatively complex and I expect there is a fair
amount of circuitry inside.
This adapter won't work with an Apple Thunderbolt display, as that
display requires a Thunderbolt connection to a computer, and won't work
with a DisplayPort (or Mini DisplayPort) video source.
> 2 connected via TB, the third via HDMI m-m cable ( techlynx) to a TB
> (f-m) adaptor;
An adapter with Mini DisplayPort and HDMI connectors is probably
receiving video via DisplayPort and outputting it via HDMI. This sort
don't work the other way around.
> bought form the local Apple independent who confirmed it would work ( note
> that is not 'should' work)
Which adapter, exactly?
> You don't know until you try, and they obviously have not yet tried. I
> raised my preference for Apple brand cables, don't have them theses will
> be ok. Having captured a lot of data form live systems over the years, I
> know a little about cable quality ramifications, but when in Rome, without
> an option...
>
> Connect the third display via HDMI, nada.
The Thunderbolt display doesn't accept HDMI input so that won't work.
You need a third display which accepts HDMI input. That means a
third-party display, not an Apple one.
> Tried the combinations, 1-2 daisy chain, 3rd to the second TB port on
> the MBP, nada. etc.
>
> TB-daisy-TB MBP runs the 2 TB, but same plus 3rd into the second MBP TB
> port nada
>
>
> Phone to Apple again.
>
> Conclusion, the web info indicates 2 TB plus HDMI. That means a HDMI
> dive, but not a TB device connected via a HDMI to TB cable/adapter.
>
> At least at the moment. That may or may not change when/if Apple have a
> cable.
>
> It is curious though, the the GPU supposedly has the grunt to run 2xTB
> display and a HDMI, but not similar pixel push over a TB combo ( daisy
> chained...) So it is presumptively a cable/adapter issue.
The graphics controllers have dedicated outputs which generate certain
types of video signals. There are enough DisplayPort outputs to drive
two displays, plus there is a dedicated HDMI output which goes to the
external HDMI connector, and whatever is needed to drive the internal
display (probably another DisplayPort signal).
There aren't enough DisplayPort outputs available from the graphics
controllers to drive three displays via Thunderbolt.
Even if there were, you can't daisy-chain three displays through a
single Thunderbolt port as each DisplayPort signal ties up half of the
available bandwidth of Thunderbolt.
With two Thunderbolt ports, the only reason you can't drive three
displays via Thunderbolt is that there are only two compatible signals
available.
> Apple as ever ( 25 years of ever), on the phone are as good as one might
> reasonably expect. Your mileage may vary, mine has always been good. No.
> 3 goes back Friday.
--
David Empson
dem...@actrix.gen.nz