Apple's A-series family tree
Chipworks presented some quantitative numbers comparing the A6 and A6X,
in their November 1st discussion
of the A6X. With a die size of 124 mm², the A6X is 28% larger than
the 96.7 mm² A6.
The CPU consumes 15 mm² on both parts, while the
triple core GPU of the A6 weighs in at 16 mm², and the quad core GPU on
the A6X comes in at 35 mm².
From the above numbers it is apparent that
beyond the additional 19 mm² for the GPU the A6X sports approximately 10
mm² additional area. This may not seem like that much, but it is
actually an area larger than the individual GPU cores.
In terms of
accounting for this additional area we can again turn to Chipworks who
noted that the A6X doubled the SDRAM interface width and included some
new interface blocks. They also observed one fewer PLL for the A6X
which freed up some mm².
So we gain some area here and use a bit less
there. The question though is whether there are other differences. We
will take a look at this, but in the context of the evolving A-series
family. A visual interpretation of Apple’s chip lineage should help.
The Family Tree
A-series family tree is presented below. Starting with the A4 in 2010
and ending with the A6X just a few months ago, there are now 5 members
in the family. Basic information for each AP, including the device in
which it was introduced, its dimensions (mm) and die size (mm2) are
included. The tree has been constructed to schematically illustrate two
major evolutions that have occurred within the family over the last
three years. First, the original family line bifurcated into two
distinct lines of APs. Second, the family went through a process
“shrink” from the original 45 nm to the current 32 nm fabrication
process. Each of these events will be considered in more detail.