# Opinion: RAM Fill TimeOpinion: RAM Fill Time

In this reprinted <a href="http://altdevblogaday.com/">#altdevblogaday</a>-opinion piece, SCEA senior software engineer Drew Thaler analyzes RAM fill time for consoles, which he says will give you a ballpark idea of how fast your game should be able to lo

Drew Thaler, Blogger

September 15, 2011

[In this reprinted #altdevblogaday-opinion piece, SCEA senior software engineer Drew Thaler analyzes RAM fill time for consoles, which he says will give you a ballpark idea of how fast your game should be able to load.] Today I want to talk about the baseline load times for games on consoles. I'm going to dive right in with the equations here, so be prepared. One of the useful metrics for understanding game load times is RAM fill time. It's more-or-less true that most console games tend to fill the available RAM entirely with very little left over. There are exceptions, of course, but it's not bad as a general rule. Similarly, we can more-or-less assume that a game can't really start until RAM is basically full. There are plenty of exceptions here too which I won't get into, but again – not a bad first order approximation. To The Math-Mobile! So: For a given hardware platform, what is the minimum time possible to fill RAM? The answer:

tfill = sRAM / vfill

where:

tfill = minimum time to fill RAM sRAM = size of RAM to fill vfill = data load speed

In plain English, the time it takes to fill a given amount of RAM is equal to the size of the RAM divided by the speed at which you can fill it. You may have noticed that I subtly weaseled a bit there. Why did I use vfill instead of, say, vdisk? Because of data compression! Many games keep their data compressed on disk and then decompress it into RAM. So the effective rate at which you can load data depends quite a lot on your compression ratio.

vfill = vdisk / rcompression

where:

vdisk = speed of the disk rcompression = compression ratio = scompressed / suncompressed scompressed = size of data after compression suncompressed = size of data before compression