differences in rendering a high resolution

good evening cg peeps, just wanna ask.. yung mga kaworkmate ko kasi, nakakapagrender sila ng high reso, but using a little setting in vray (like yung frame buffer naka-off ) but yung specs nila is 32bit 2gb ram 1g vcard.. ang question ko is, what's the difference between frame buffer vray at frame buffer ng custom?.. thanks CGP!