Is The PS3 A Blu-Ray Trojan Horse?

OK, lets look at this with numbers.

First of all, I was mislead by Wikipedia above, the Blu-ray 1X data transfer speed is 36 MBits/s. The 54 number appears to be for movies as players are required to spin at 1.5X for movie playback.

Anyway, the average seek time I've seen quoted for Sony-made Blu-ray drives is 210 ms, or the equivalent of reading 1.89 MBytes from the Blu-ray disc in a PS3 (36/8*2/1000*210). So if you are reading 1.89MBytes from disc, seek times are likely to be half of the total time to retrieve that data.

If you can double up the data stored on the disc and organise it to minimise seek times, you could theoretically half the average seek times to 105 ms, or the equivalent of reading 0.945 MBytes from disc, or 967 KBytes. Reading our 1.89 MBytes file now has only a third of the time spent seeking the data as opposed to reading it.

So what effect does this have on typical file sizes? Here is a chart I've just nocked up showing how fast you can read a set of file sizes with Blu-ray single data, Blu-ray doubled data and 12XDVD. I've assumed a 170ms seek time for DVD since that's what the page above says for the Sony Blu-Ray drive.

0.5MByte - 9.266s - 0.161s - 0.203s
1MByte - 0.321s - 0.216s - 0.236s
1.5MByte - 0.377s - 0.272s - 0.269s
2MByte - 0.432s - 0.327s - 0.302s

As you can see, once you get to 1.5MBytes, the DVD drive wins out due to its higher transfer rate, the amount of data is outweighing the time taken to seek. So to randomly find files under 1.5MBytes on the disc, the doubled up data idea works really well.

However, here's the bad news. Most of the time with loading levels for games, you seek once then read the whole thing in one go. Multiple megabytes in a go, filling the memory of the console. This applies to games with streaming data too, since you have to load the data required for the first section of the level before you can start to stream anything and this initial load is where players will notice the delay.

Once the initial data is loaded, you have more opportunity to load different models, textures and the like by streaming them in as the player navigates the level. This is where the double data method will really shine, but it can't be used for game like Shadowrun, for exmaple, where the player can teleport to other areas and will expect no lag.

Doubling up your data is a method that apparently works well with Oblivion, but may not work so well with other games. Other games may require a lot of optimisation of data for it to work. It's all swings and roundabouts, but for that initial load, higher rates of data transfer are much, much better.