The notes below are our 2nd attempt to put ARM onto our radar (the 1st attempt being a Wisconsin university report on power performance comparison of RISC based on ARM versus CISC based on Intel Core i7).  We will briefly paint a picture of who ARM is based on information publicly available such as Wikipedia and ARM websites.  Info here takes a system integrator perspective.

o ARM is based in UK and stood for Acorn RISC Machine initially.  Its website is www.arm.com. ARM is a well known brand these days and it has possibly a larger share of the CPU chip level market in the world in terms of quantity (not revenue) than other chip makers.  However, ARM is not a chip maker.  ARM is a chip circuit architecture designer and earns its revenues from licensing the design to chip makers such as Nvidia, Qualcomm, Texas Instruments, etc.  Previously ARM was used in mobile devices.  Recently ARM has turned up in servers extending its applicability and visibility by a huge range. 

ARM has trade-marked this term big.LITTLE and operates http://www.thinkbiglittle.com/.  This is a System-on-Chip (SOC) scheme meaning that some member chips can be high performance and some members can be low wattage and they work together as a “chip system” or CPU in PC terminology.  Software workloads are dynamically and instantly transitioned to the appropriate member chip based on performance needs.  This scheme would reduce energy consumption in the CPU by 70% on background tasks & 50% for moderately intense work. 

o Nvidia Tegra4 used in mobile devices is a good example of SOC.  It consisted of 5 CPU cores (4 large and 1 small ARM cores) and 72 Geforce cores.  The large CPU cores are for running user applications and the small core is for the period when the device is not being active.  This scheme enables fast responses to user requests and low wattage consumption at other times.

 ARM has a large range of processor products designed over the years.  Herewith at 2013-04 we reveal the more recent products as in ARMv7 and v8 micro-architectures without going into technical depth.  From the table we can tell that Cortex-A5 and A7 are smaller (or lesser performance) than Cortex-A8, A9, A15 within ARMv7, which in turns is smaller than ARMv8.

o NEON is a distinct feature of recent ARM processors.  NEON is a name trade-marked by ARM for its SIMD instruction architecture which stands for Single Instruction Multiple Data.  Intel and AMD x86 CPU models named their SIMD schemes as SSE1, 2, 3, 4 etc previously and AVX 1, 2 recently.  NEON is different to SSE and AVX.  NEON has 64 registers of 64b width or 32 registers of 128b width. These registers process the same instruction with different multiple data simultaneously.  They provide parallel processing capacity.

Most if not all Android smart phones are based on ARM as in 2013-04.  An AMD division called SeaMicro is designing servers based on 512 ARM cores to provide 1.28Tb/s of memory bandwidth (reference: Nvidia Kepler K20X claimed 200GB/s or 1.60Tb/s).

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