Advice on which cable needed

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Hey guys i'm due to get my new monitor which will be DVI connected but i'm currently using a very old monitor which only supports VGA. I want a connector that I can use for dual monitors but my GFX card has only one DVI port on it, which Y splitter cable do I need for it to be DVI connected but on the other end has 1 DVI connector and 1 VGA connector?
 
I assume you would like to drive them in "extended desktop" mode (as in not "clone" mode)? With splitters, this won't be possible, and trying that might even damage the hardware itself. And even the clone mode probably requires an active splitter, meaning a powered hub. If on the other hand, you want to drive only one monitor active at a time, then it might be possible. In that case, you could also try a KVM switch.

In any case, I would recommend to purchase a new GPU, as it will probably become cheaper and certainly less hassle.

BUT:
If you mean that you don't intend to use the monitors at the same time at all, meaning you would first use the splitter to drive the old monitor, and once the new monitor arrives, you will just toss the old monitor to the bin, and only use the new monitor with the splitter, then sure, the splitter will work for that sort of thing. But considering you would need to buy a new cable in any case, I would just buy the regular DVI-DVI cable to use with the new monitor, and use the old cable with your current setup for the time being.

Which scenario are you after?
 
What i'm after is i'm getting a BenQ monitor shortly which will be run under DVI connected, my current monitor at this moment is a 17inch tft old VGA monitor, I want this old monitor to show my desktop only while I play games on my new monitor for streaming purposes. While also playing a game on my main monitor I would like to surf the internet and such on the small old VGA monitor. My GFX card is ATIHD 7850 Power Edition which comes with one DVI port, 1 hdmi port and 2 mini ports. I want to run the BenQ monitor in 120hz which is why the DVI is required other than a HDMI lead for 1080p.

So both monitors are connected to a Y splitter cable which will go into my GFX card but have one DVI connector and one VGA connector so both monitors are active (I don't have enough room to fit 2 24inch monitors on my desk). All i want is the old VGA monitor to show the desktop only and not show any games being played so when streaming I can see twitch chat on the old VGA monitor.
 
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Simply put, unfortunately you can't run two vastly different signals from a single port. In this case, you would need to run them on different frequencies, probably different resolutions, and even having them on extended mode (so not cloned). Furthermore, you would need to run both analog and digital signals within the same cable. Not possible. You might have to fiddle a little bit even if you run them on different ports (the frequency difference is the biggest concern, I think).

In any case, your only option would be to run the VGA monitor through the GPU's DVI port, which is currently your GPU's only port supporting analog signal transmission. If I understood correctly, this is the current setup?

As for 120/144Hz, your GPU's only options are mini-DisplayPort and DVI (assuming it supports DL-DVI). Unfortunately, the BenQ doesn't seem to have a DisplayPort of any kind on it, and the DVI would have to be preserved for the VGA. Therefore your only option would be to try a miniDP-to-DVI adapter (edit: link removed, not applicable), but I have no certainty whether that will work with 120/144Hz (edit: only active adapters might, but apparently not all of them will). But other than that, there aren't any other options I can think of with the current components.
(and this is assuming that the previously stated "mini port" is indeed mini-DisplayPort)
(also, I wouldn't be so sure that there's a DVI cable included with the monitor, so you'd better check before purchase -- and if not, then make sure you get a dual-link compatible cable)
(edit: judging from the user reviews, there is a dual-link DVI cable included with the BenQ monitor)

In summary:
Old monitor: GPU DVI --> monitor VGA (with the current cable)
New monitor: GPU mDP --> monitor DVI (with mDP-DVI adapter + DVI-DVI) (edit: will cost around £80, and no guarantees it would work)
 
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What about if i scrap the dual monitor for now till i get my upgrade and use the DVI lead if it comes with the monitor directly into my GFX card will that run 120/144hz?

Forgot to ask does the monitor even come with a DVI lead or do I need to buy one?
 
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Well, that would depend on whether the GPU's DVI port supports dual-link. But no worries, it certainly should, as 7850 is a higher end card, so no reason why they would decide to skimp on that. I'm 90% certain it should be OK.

As for included DVI with the BenQ: yes, it appears there is one with the box (at least one user review states this: "the bundled DVI-D worked perfectly").

But, with regards to the mDP-DVI adapter working with 120/144Hz:
From a quick search, it would seem like 120Hz is possible only with some active adapters, where the power is through USB. But some people report having problems even with those. Even OCUK stocks one of these, but it doesn't state anything about 3D or 120Hz, so it might not work for you.

And in any case, they cost around £80, so I wouldn't recommend them.

(I edited my previous post to correct these matters.)
 
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