We can't tell you.
We need a lot of information: your OS, version of AE, Processors & cores, your storage capacity, the kind of footage you'll be working with and the files that you intend to deliver.
For After Effects CS6, Adobe recommends 8GB, although they say it can work with only 4GB.
Here's a helpful FAQ about what information to include when asking questions on forums:
We need to know a lot more to help you. Please provide answers to the questions listed here: "FAQ: What information should I provide when asking a question on this forum?"
ok well i have got a AMD 4 core 3000ghz , 6 gig ddr 3 1333 mhz memory 2x 1tb hard disk and 1x 1,5 tb
i have got a nvidia 240 gt video card with 1 gb memory and i.m working on windows 7 sp1 64 bit os and AE cs 5
i have made an partition from 80 gb as work space only for AE
and it works mostly fine but when i am rendering a short movie (from 2 minutesor so) it s keep saying multiprocessing disabled and short of ram
i hope this is enough information and sorry for my english i'm from holland and not so verry good with english writing
You have 4 cores, a good amount of storage, but a small amount of memory. People still must guess about the kind of work you will do in AE.
6 GB RAM is a very small amount of memory for After Effects Work. if you can get your machine up to 16 GB RAM, you will have enough to use multiprocesing.
I can and have run AE CS6 on a MacBook (black plastic) with only 2 GB because that's all it will take. If you use your head and don't try to do too much at once CS6 performs as well as CS5 or 5.5 on this little wimpy machine. It works much better on a MacBook Pro Retina that's maxed out on ram.
The simple answer to how much memory do you need is as much as you can afford but at least 4GB per core for MP rendering with standard plug-ins. The simple answer to what kind of display adaptor do you need is in the list of recommended CUDA cards in this list. BTW, the NVIDIA GeForce GT 650M in the MBPro R works just fine for Ray Tracing if you run add it to the list using terminal commands. With Graphics/Display cards you also pretty much get what you pay for. The more cores, the more memory, the better CUDA will work.
Throw in 3rd party plug-ins, codecs, and a bunch of other variables and you'll have to experiment.