I bought an iMac from Apple last year, in October 2011.

It was described as :

Refurbished iMac 21.5-inch 3.2GHz Intel Core i3 processor, 2010 model.

And we have been very happy together.

Now, I want a DVI cable to run a 2nd screen, and while I'm used to chucking away $20-30 on cables that don't work, I thought this time I'd ask the Gurus first.

There is apparently a different version from earlier iMacs (up to about 2010/11) and post 2010/11. One is Mini DVI to VGA, the later is Mini Display Port to VGA.

Any clues as to which one I would have? I suspect it'd be the earlier, but tell me and save me a few quid!