Triple layer Blu-Ray recordable discs

[dbminter]

Okay, so, I'm a little confused.  Single layer Blu-Rays are a standardized 25 GB.  It's a nice, rounded number.  Not some arbitrary space size like 700 MB CD's or 4.7 GB DVD's.  Then there's the double layer Blu-Ray, which is 50 GB.  Which makes sense.  It's twice the size of a single layer Blu-Ray and has 2 layers, 2 25 GB layers.  Along comes triple layer Blu-Ray and here's where it makes no sense! 

 

 

How can triple layer Blu-Ray be 100 GB?    The only way this seems to make any sense is if one layer is 50 GB and then the other 2 layers are 25.  Does that mean double layer Blu-Ray actually only has 1 50 GB layer in it?  Then why call it double layer?

 

 

And then there's quadruple layer Blu-Ray with the seemingly arbitrary value of 128 GB!    Actually, from a computer science POV, 128 is a common value as it's a multiple of 2.

[LIGHTNING UK!]

They changed the layer size when going to triple / quad.

[dbminter]

So there is a 50 GB layer in triple layer Blu-Rays?  Then for quadruple layer Blu-Rays they made the somewhat arbitrary layer size 32 GB?  Then the triple layer ones should have been 96?

[LIGHTNING UK!]

No, I meant when going from 1 / 2 layers to 3 / 4 layers. I'm sure it's all in the spec sheet somewhere if you can find it

[dbminter]

I'll try to find the spec sheet for Blu-Ray, then. 

[dbminter]

I couldn't come across anything that explained the size of each layer for XL and quadruple layer BD discs.

 

 

EDIT: Found the white sheet for TL/QL BD.

 

 

http://blu-raydisc.com/Assets/Downloadablefile/BD-R_physical_specifications-18326.pdf

 

 

TL layers are 33.3 GB.  So, BD XL is not actually 100 GB but 99.9.    And as I surmised, QL are made up of 4 32 GB layers.  So, they did increase the size of the single layers found in the TL and QL discs.