i have intel dh55tc mobo and win 7 64 bit. Earlier I had 2x2gb ram (same model, dual channel) but now one of the ram stick got faulty and am left with just 2gb ram. i can't find the same ram model to replace the faulty one and also i'm thinking of upgrading to 6gb ram. so should i go for 2gb(old)+2x2gb (new)ram configuration or a 2gb(old)+1x4gb(new)?
Most RAM caries a Lifetime Warranty so I'd get the bad stick replaced and if needed get a matching set to the 2x2GB that you already have and you'll have 8GB otherwise get a 2x4GB set and use the 2GB as a paperweight.
+1 to Jaquith To OP - you will lose Dual Channel mode if you put 2gb(old)+2x2gb (new), or 2gb(old)+1x4gb(new).