Default-free BGP

From NANOG

"How much RAM?" seems a subset of issues with being in the DFZ. Not sure what the other items should be, but global propagation timing, cpu/churn, flap dampening, best practices/policies, etc might apply here. If you think different, edit away!

Memory Requirements

The precise answer to this question depends on what BGP sessions your router will have configured, who those BGP sessions will be with, what kind of router it is and what ingress policy you apply to the routes you learn. The only good way to find a precise answer is to set the router loose in the intended configuration and measure.

A more practical answer for someone who needs to deploy a BGP speaker that will terminate a couple of full (transit) sessions plus a few more internal and peering sessions at the time of writing is 1GB. You may well be able to get by with less, but you're unlikely to get into too much trouble with 1GB. For hardware longevity, "The most your budget will allow" is a safe bet.