i have the option of buying zotac gt 240 ddr5 1gb or powercolor hd 5570 ddr3 1 gb both for rs.3300 but the only difference is of direct x gt240 only supports dx 10 while hd 5570 supports dx 11 which one should i go for??one is ddr5 with dx 10 and other ddr3 with dx 11 which is better? my budget is limited and psu is 250 w(iball)
The seem to be pretty evenly matched (about a 3% difference in the gt240's favor). Also, gt240 has dx 10.1, which shares some features with dx 11. And since your PSU will be able to power them both, I'd go for the gt240 just for the gddr5.
if you're set on those two cards only, then get the one you like. imo both have comparable performance. gt 240 may a bit faster than the 5570. 5570 supports directx 11 while the gt240 supports directx 10.1. neither are good for gta 4 ,crysis 2 (these two aren't casual games lol) gaming at medium-high settings. you might have to turn down gfx options to get higher fps out of those cards.
crysis 2, gt 240 gddr5 vs 5570 (and 6570) http://www.tomshardware.com/reviews/radeon-hd-6570-rade...
5570 performance, gta 4 eflc @ medium settings http://www.tomshardware.com/charts/2011-entry-level-gra...
edit: gta 4 likes strong cpu and system ram. if you have a good cpu cooler, you can try oc your cpu.
If you're going to go for the GT 240 then get the DDR5 version for $10 more, it's significantly faster.
The real problem you're going to have though is your PSU. 250W is insufficient for either of those cards. If you put one of those in then don't be surprised if you have stability issues or random crashe. The GPU can pull around 75W plus your CPU at around 100W, the motherboard/RAM at 50W and any fans or accessories will put your system right at the maximum output of your PSU for any demanding gaming.
my last question- is dx 11 a necessary thing that games coming in 1-2 yrs will not even run on dx10 card??
directx 11 is advantegeous over dx 10.1 or 10. as more and more games begin to support dx 11, it's useful to have it's support. but, neither of the gpus you selected can run dx11 games at their high settings and falling back on dx10 might improve fps in games at the expense of visual quality. what's worse, you'll have to buy yet another more powerful card (imo you actually need a whole new pc for gaming) soon, to play newer games at high settings, and the cycle will continue. what i'm saying is, at your price limit and choices, it doesn't really matter imo.