Yesterday, ifixit tore down the new iPad, revealing the new A5X processor.
http://www.ifixit.com/Teardown/iPad-3-4G-Teardown/8277/3
Chipworks, a similar tear down company (that also does die x-rays, hopefully forthcoming for the A5X), also took a look at the guts here:
http://www.chipworks.com/en/technic...downs/2012/03/first-look-inside-the-new-ipad/
http://www.chipworks.com/en/technical-competitive-analysis/resources/recent-teardowns/2012/03/the-new-ipad-a-closer-look-inside/
A look at the A5X with the heat spreader off
Top view of iPad logic board
1GB DRAM, 2 packages, not on CPU package (bordered in yellow)
The biggest shift that can be seen here is that the DRAM is no longer located on the same package as the CPU die. This is normally done to save space in a mobile device and is referred to as PoP (package on package). It is beneficial in that it saves space and it saves routing relatively high speed data lines on your logic board. The main disadvantage is reduced ability to conduct heat away from the CPU. However, this normally isn't a problem for low power CPUs. So, given these advantages, it seems likely that Apple moved the DRAM dies away from the CPU to allow heat to be conducted away from the CPU better. I asked Anand Shimpi from the respected anandtech if he agreed with that assessment, and he did. (https://twitter.com/#!/anandshimpi/status/180632702750429187)
So, why does this spell trouble for the next iphone? Well, the iphone has a lot smaller space and tighter thermal constraints. Apple has downclocked the A4 and A5 CPUs about 20% from their respective iPad clocks for battery life as well as thermal concerns. If they are forced to move the DRAM off package for the A5X, it simply won't fit in the next iPhone, which doesn't have space for extra DRAM packages on the logic board. If they put the DRAM on the package, they would likely have to severely underclock it to meet power and thermal constraints (remember, the iPad 3 battery is 70% bigger. The A5X, LTE and new retina screen really use power!). At some point, underclocking no longer becomes efficient for processors. It's simply too much logic clocked low. Imagine having a V12 engine you could only run at 2000 RPM. It's much better to have a V6 you can run at 8000 RPM as it is better able to adjust to dynamic power demands.
So, what will the next iPhone have? Well, if the A6 rumors are true and it has a quad core CPU, it seems likely it will have a Tegra 3-like configuration with 4 A9 CPU cores and some more modest GPU configuration, perhaps a repeat of the 543MP2. It's important to note that Apple could take an aggressive route and A6 could feature a next generation CPU core (Cortex A15, both Samsung and Nvidia will launch an A15 core this year) or GPU core (ImgTec 600 series, or "Rogue"). Both of these would represent a significant boost in computing power, clock for clock and would be the most efficient way to improve performance in the same die size and power budget. Traditionally, Apple has been rather aggressive in their CPU roadmap (the A5X is the undisputed GPU powerhouse aside from the Vita), so it seems anything is possible.
edit: Now that chipworks has seemingly confirmed they are still using the samsung 45nm process, that opens apple's options up a bit. A 32nm or 28nm shrink of the A5X may be able to work. The other options above still hold true as well. It seems very unlikely that Apple will stick with a 45nm process if the next iphone features anything other than the A5 of the iPhone 4S.
Further reading: (A5X likely built on 32nm samsung process) http://www.anandtech.com/show/5681/apples-a5x-die-and-size-revealed
edit: Chipworks now disagrees with this and says it looks like the 45nm process is still in use. See second chipworks link above.
Disclaimer: The Playstation Vita has a quad core CPU and GPU, and is very similar to the A5X. They essentially have the same GPU, but the Vita has a 543MP4+, the + indicating some undisclosed logic. The quad core CPU is likely different in its implementation of core logic as the A5 is apple customized and much larger than the vanilla A9 core. The Playstation Vita has all 512MB + 128MB of its RAM directly on the package, suggesting it can be cooled sufficiently in that configuration. This could possibly mean that the A5X had its RAM moved off chip for other reasons, but you have to keep in mind that the iPad and Vita likely deal with heat differently as their logic board shapes differ in addition to be very different devices.
http://www.ifixit.com/Teardown/iPad-3-4G-Teardown/8277/3
Chipworks, a similar tear down company (that also does die x-rays, hopefully forthcoming for the A5X), also took a look at the guts here:
http://www.chipworks.com/en/technic...downs/2012/03/first-look-inside-the-new-ipad/
http://www.chipworks.com/en/technical-competitive-analysis/resources/recent-teardowns/2012/03/the-new-ipad-a-closer-look-inside/
A look at the A5X with the heat spreader off
Top view of iPad logic board
1GB DRAM, 2 packages, not on CPU package (bordered in yellow)
The biggest shift that can be seen here is that the DRAM is no longer located on the same package as the CPU die. This is normally done to save space in a mobile device and is referred to as PoP (package on package). It is beneficial in that it saves space and it saves routing relatively high speed data lines on your logic board. The main disadvantage is reduced ability to conduct heat away from the CPU. However, this normally isn't a problem for low power CPUs. So, given these advantages, it seems likely that Apple moved the DRAM dies away from the CPU to allow heat to be conducted away from the CPU better. I asked Anand Shimpi from the respected anandtech if he agreed with that assessment, and he did. (https://twitter.com/#!/anandshimpi/status/180632702750429187)
So, why does this spell trouble for the next iphone? Well, the iphone has a lot smaller space and tighter thermal constraints. Apple has downclocked the A4 and A5 CPUs about 20% from their respective iPad clocks for battery life as well as thermal concerns. If they are forced to move the DRAM off package for the A5X, it simply won't fit in the next iPhone, which doesn't have space for extra DRAM packages on the logic board. If they put the DRAM on the package, they would likely have to severely underclock it to meet power and thermal constraints (remember, the iPad 3 battery is 70% bigger. The A5X, LTE and new retina screen really use power!). At some point, underclocking no longer becomes efficient for processors. It's simply too much logic clocked low. Imagine having a V12 engine you could only run at 2000 RPM. It's much better to have a V6 you can run at 8000 RPM as it is better able to adjust to dynamic power demands.
So, what will the next iPhone have? Well, if the A6 rumors are true and it has a quad core CPU, it seems likely it will have a Tegra 3-like configuration with 4 A9 CPU cores and some more modest GPU configuration, perhaps a repeat of the 543MP2. It's important to note that Apple could take an aggressive route and A6 could feature a next generation CPU core (Cortex A15, both Samsung and Nvidia will launch an A15 core this year) or GPU core (ImgTec 600 series, or "Rogue"). Both of these would represent a significant boost in computing power, clock for clock and would be the most efficient way to improve performance in the same die size and power budget. Traditionally, Apple has been rather aggressive in their CPU roadmap (the A5X is the undisputed GPU powerhouse aside from the Vita), so it seems anything is possible.
edit: Now that chipworks has seemingly confirmed they are still using the samsung 45nm process, that opens apple's options up a bit. A 32nm or 28nm shrink of the A5X may be able to work. The other options above still hold true as well. It seems very unlikely that Apple will stick with a 45nm process if the next iphone features anything other than the A5 of the iPhone 4S.
Further reading: (A5X likely built on 32nm samsung process) http://www.anandtech.com/show/5681/apples-a5x-die-and-size-revealed
edit: Chipworks now disagrees with this and says it looks like the 45nm process is still in use. See second chipworks link above.
Disclaimer: The Playstation Vita has a quad core CPU and GPU, and is very similar to the A5X. They essentially have the same GPU, but the Vita has a 543MP4+, the + indicating some undisclosed logic. The quad core CPU is likely different in its implementation of core logic as the A5 is apple customized and much larger than the vanilla A9 core. The Playstation Vita has all 512MB + 128MB of its RAM directly on the package, suggesting it can be cooled sufficiently in that configuration. This could possibly mean that the A5X had its RAM moved off chip for other reasons, but you have to keep in mind that the iPad and Vita likely deal with heat differently as their logic board shapes differ in addition to be very different devices.
Great informative posting.
