This article is pretty obviously a collection of rumors and speculations being thrown around here and at B3D.
Using the 68 GB/s number for memory bandwidth (literally came from someone at B3D who was merely speculating) the author assumes that MS went with the highest available JEDEC DDR3 spec (2133) which I find unlikely given how modestly spec'd the rest of machine is. Looking at Micron's spec sheet the highest density IC at that speed is 4 Gb which means they'd have to use 16 chips to make the rumored 8 GB pool. This would majorly affect board complexity and reduce reliability. In my opinion this is a non option.
It's likelier they'll go with 8 denser 8 Gb chips with DDR3-1866 or even DDR3-1600(L) spec which would put theoretical unified bandwidth at 50 - 60 GB/s. Using a separate faster pool (eDRAM) as a framebuffer mitigates the speed discrepancy as the GPU doesn't have to write back to the unified main RAM nor fetch from it for post-processing effects like with the rumored PS4 setup.
The article also fails to account for rumored "two additional graphics blocks" which in my opinion are the 2 radeon compute units attached to the CPU for GPGPU purposes (also rumored for PS4). According to rumors, both systems seem to be comprised of an AMD Jaguar based APU (CPU + tiny GPU) and a GPU integrated on the same die via differently configured custom memory controllers. As such their relative performance will be easier to compare than with previous generations of consoles IMO.
Using the 68 GB/s number for memory bandwidth (literally came from someone at B3D who was merely speculating) the author assumes that MS went with the highest available JEDEC DDR3 spec (2133) which I find unlikely given how modestly spec'd the rest of machine is. Looking at Micron's spec sheet the highest density IC at that speed is 4 Gb which means they'd have to use 16 chips to make the rumored 8 GB pool. This would majorly affect board complexity and reduce reliability. In my opinion this is a non option.
It's likelier they'll go with 8 denser 8 Gb chips with DDR3-1866 or even DDR3-1600(L) spec which would put theoretical unified bandwidth at 50 - 60 GB/s. Using a separate faster pool (eDRAM) as a framebuffer mitigates the speed discrepancy as the GPU doesn't have to write back to the unified main RAM nor fetch from it for post-processing effects like with the rumored PS4 setup.
The article also fails to account for rumored "two additional graphics blocks" which in my opinion are the 2 radeon compute units attached to the CPU for GPGPU purposes (also rumored for PS4). According to rumors, both systems seem to be comprised of an AMD Jaguar based APU (CPU + tiny GPU) and a GPU integrated on the same die via differently configured custom memory controllers. As such their relative performance will be easier to compare than with previous generations of consoles IMO.