Question: Jim Keller is a microprocessor engineer most well known for his work at AMD and Apple, he was involved in designing which 32-bit package on package (PoP) system-on-a-chip (SoC) designed by Apple Inc. and manufactured by Samsung? 

Context paragraphs:
Apple A5: The Apple A5 is a 32-bit system-on-a-chip designed by Apple Inc. and manufactured by Samsung and is the successor to the Apple A4.  The A5 commercially debuted with the release of Apple's iPad 2 tablet, and also powers the iPhone 4S, iPod Touch fifth generation, Apple TV third generation, and the iPad mini.  This is consistent with how Apple debuted the A4 chip: first in the original iPad, followed by the iPhone 4, and then the iPod Touch (fourth generation).  Apple claims that compared to its predecessor, the A4, the A5 CPU "can do twice the work" and the GPU has "up to nine times the graphics performance".

Athlon 64: The Athlon 64 is an eighth-generation, AMD64-architecture microprocessor produced by AMD, released on September 23, 2003.  It is the third processor to bear the name "Athlon", and the immediate successor to the Athlon XP.  The second processor (after the Opteron) to implement AMD64 architecture and the first 64-bit processor targeted at the average consumer, it was AMD's primary consumer microprocessor, and competes primarily with Intel's Pentium 4, especially the "Prescott" and "Cedar Mill" core revisions.  It is AMD's first K8, eighth-generation processor core for desktop and mobile computers.  Despite being natively 64-bit, the AMD64 architecture is backward-compatible with 32-bit x86 instructions.  Athlon 64s have been produced for Socket 754, Socket 939, Socket 940 and Socket AM2.  The line was succeeded by the dual-core Athlon 64 X2 and Athlon X2 lines.

Apple A10: The Apple A10 Fusion is a 64-bit ARM-based system on a chip (SoC), designed by Apple Inc. and manufactured by TSMC.  It first appeared in the iPhone 7 and 7 Plus which were introduced on September 7, 2016.  The A10 is the first Apple-designed quad-core SoC, with two high-performance cores and two energy-efficient cores.  Apple states that it has 40% greater CPU performance and 50% greater graphics performance compared to its predecessor, the Apple A9.

Apple A4: The Apple A4 is a 32-bit package on package (PoP) system-on-a-chip (SoC) designed by Apple Inc. and manufactured by Samsung.  It combines an ARM Cortex-A8 CPU with a PowerVR GPU, and emphasizes power efficiency.  The chip commercially debuted with the release of Apple's iPad tablet; followed shortly by the iPhone 4 smartphone, the iPod Touch (4th generation), and the Apple TV (2nd generation).  It was superseded by the Apple A5 processor used in the iPad 2 released the following year, which was then subsequently replaced by the Apple A5X processor in the iPad (3rd generation).

List of AMD K5 microprocessors: The AMD K5 microprocessor is a Pentium-class 32-bit CPU manufactured by American company Advanced Micro Devices (AMD), and targeted at the consumer market.  It was the first x86 processor designed by AMD from the ground up, and not licensed or reverse-engineered as previous generations of x86 processors produced by AMD.

Apple A5X: The Apple A5X is a 32-bit system-on-a-chip (SoC) designed by Apple Inc., introduced at the launch of the third generation iPad on March 7, 2012.  It is a high performance variant of the Apple A5; Apple claims it has twice the graphics performance of the A5.  It was superseded in the iPhone 5 and 5C by the A6 chip and the fourth generation iPad by the A6X chip.

Jim Keller (engineer): Jim Keller is a microprocessor engineer most well known for his work at AMD and Apple.  He was the lead architect of the AMD K8 microarchitecture (including the original Athlon 64) and was involved in designing the Athlon (K7) and Apple A4/A5 processors.  He was also the coauthor of the specifications for the x86-64 instruction set and HyperTransport interconnect.  From 2012 to 2015, he returned to AMD to work on the AMD K12 and Zen microarchitectures.

Apple A9: The Apple A9 is a 64-bit ARM-based system-on-chip (SoC), designed by Apple Inc.  Manufactured for Apple by both TSMC and Samsung, it first appeared in the iPhone 6S and 6S Plus which were introduced on September 9, 2015.  Apple stated that it had 70% more CPU performance and 90% more graphics performance compared to its predecessor, the Apple A8, and was one of the most powerful and energy-efficient mobile chips on the market then along with the Samsung Exynos 8890 and Qualcomm Snapdragon 820.

Apple A6: The Apple A6 is a 32-bit package on package (PoP) system on a chip (SoC) designed by Apple Inc. that was introduced on September 12, 2012 at the launch of the iPhone 5.  Apple states that it is up to twice as fast and has up to twice the graphics power compared with its predecessor, the Apple A5.

Apple A6X: The Apple A6X is a 32-bit system-on-a-chip (SoC) designed by Apple Inc., introduced at the launch of the fourth generation iPad on October 23, 2012.  It is a high-performance variant of the Apple A6.  Apple claims the A6X has twice the CPU performance and up to twice the graphics performance of its predecessor, the Apple A5X.

Supporting paragraphs: Jim Keller (engineer) Apple A4
Answer: Apple A4