System RAM in PS3 and XBox 360 is like half a GB

[selnor]

Also @ the OP. The 360 runs GDDR3 512mb. Most Pc's still use DDR2. As already mentioned Vista for instance plus all the virus protection systems running in the background also take up PC memory, so it is far closer than you imagine. DDR3 ram is alot more efficient than DDR2.