how game with requirement 64mb graphic card 500mb ram works with no card 4gb ram?

I want to know how game requirement changes with change in ram cpu etc.
is there a perfect way to know how much of ram or cpu can take place of certain mb of graphics card if is please help me

The Skinnerz is right; he beat me to it. Older games will do with the motherboard's built-in graphics and a nice amount of RAM; while new ones will need a dedicated graphics/video card.
There is no substitution for the graphics card. More CPU power and system RAM isn't going to magically make the onboard graphics perform outstanding feats.

The system requirements for the game break down into 2 needed categories; System and video.

Not enough system RAM and the game has to do more loading from the HDD slowing things down. If you don't have enough CPU power then the info isn't able to be processed fast enough. SO the video card doesn't get the info it needs to render the scenes as fast as it needs. Not enough video RAM means the card can't hold the large volume of data needed to render high resolution scenes. Not enough video processing power means the card isn't able to render the scenes very fast. All of this contributes to how laggy the game play is and your overall FPS. Not enough of one thing will slow down the entire experience.
Graphics memory, and the main RAM installed in the PC are different things.

For older or less demanding games, the integrated graphics, which are built into the CPU can be sufficient. These use some of the RAM as video memory. For newer, or more demanding games you need a dedicated graphics card, which has it's own memory built in, typically a lot more than integrated graphics can access.

As for CPU and RAM, anything with the same or higher speed and capacity that required will be able to run the game.