displayimac
I want to buy a 27 inch iMac, but the monitor cannot be re-used… it cannot be hooked up to any KVM (Keyboard / Video / Mouse) switch to be used with a PC too…
Also, 3, 4 years down the road, I know the iMac will become slow and probably need to buy another computer. At that time, what am I going to do with the monitor? Apple is saying they save the "microwatt" between your typing, but what about wasting a good monitor like that?
This application allows you to use exactly what you have described; the mouse is 'teleported' to the other screen when moving to its edge. It finds computers using Bonjour and sends events over TCP. Note that it is a preference pane utility (found in System Preferences).
Thunderbolt-equipped iMacs prior to iMac (Retina 5K, 27-inch, Late 2014) (see this document), like your iMac (Mid 2011), support Target Display mode:
Target Display Mode lets you use your iMac as the external display for another, “primary” computer.
NOTE: This won't work for iMac (Retina 5K, 27-inch, Late 2014) and later iMac models as they don't support Target Display Mode.
If you happen to own a laptop with a Thunderbolt port follow these simple steps to extend your display (Thunderbolt to Thunderbolt cable required) (from KB PH4469):
(As a side note: Older iMacs with Mini DisplayPort also support Target Display Mode. The steps to configure and enable Target Display mode are very similar.).
A comment on DVI to Thunderbolt adaptors
You can't use Mini DisplayPort to DVI or VGA adaptors:
to connect a computer with a DVI/VGA port to a Thunderbolt display (from this thread):
I can confirm that Mini DisplayPort to DVI converter works ONLY from a Mini DisplayPort computer port to a DVI display. The reverse direction is not supported by those converters,
There is some hope, though, as the post goes on to say:
but there are other much more expensive ones that will convert DVI computer ports to Mini DisplayPort display.
The poster is probably refering to a product mentioned earlier in the thread: the Kanex C247D Single-Link DVI to Mini DisplayPort Converter, advertised like this:
Connect a (...) LED Cinema Display to your DVI-equipped MacBook Pro, Mac Mini, or PC with this (...) Kanex solution.
However, opinions diverge on whether it will work with a Thunderbolt display at all:
I am sure that Kanex don't do anything that will help you no matter how expensive it may be.
As far as I am aware, and I have done a lot of reading about this, you can connect an older display to the new Thunderbolt port of a new MAC but you CANNOT connect the Thunderbolt display to anything other than a MAC with a Thunderbolt port. The Kanex thing works from a Thunderbolt port into an older display, DVI or whatever but you cannot convert MAC DVI into Thunderbolt......I think
I've noticed that the LED Cinema Display is listed as a Mini DisplayPort display (from http://support.apple.com/kb/SP502):
so the adaptor may indeed only work with Mini DisplayPort displays, not with Thunderbolt displays, and as far as I can tell, your iMac will act like a Thunderbolt display.
It's up to you to try it, although $129.90 (as of this writing) is a steep price to pay for the Kanex adaptor just to test it.
If the solutions described above aren't feasible or cost-effective, you can use several software solutions. One is Air Display:
Use your iPad, iPhone, Android, Mac or Windows PC as a second (or third) monitor with no messy cables or wires
There is a free trial version here.
Note: Windows 7 Starter edition is not supported.
Best Answer
The display port on the latest iMac's (actually since late 2009) acts as both an output (for an external display) or an input (to make the imac screen a monitor).
See http://smokingapples.com/asides/new-27-imac-doubles-up-as-external-monitor/