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Snapdragon 850 to Power Arm PCs

July 3, 2018

Author: Mike Demler

Qualcomm has announced a new Windows 10 on Arm platform for always-connected PCs, the Snapdragon 850. It uses the same Snapdragon 845 chip as Galaxy S9/S9+ smartphones and includes the company’s RF front end.

For notebooks, the company bumps up the Cortex-A75 CPU’s maximum clock frequency to 2.96GHz, just 6% faster than the smartphone specification. That speed matches Arm’s projected maximum for the A75 in 10nm technology. The 6% boost doubles the typical CPU power consumption from 1W to 2W, but notebooks have 10x more battery capacity and larger thermal budgets that can accommodate the tradeoff. The Adreno 630 GPU’s operating conditions remain the same as in smartphones.

The Windows 10 on Arm strategy targets always-connected PCs (ACPCs) that deliver more than 20 hours of battery life. But only a few Windows Store apps—such as Outlook—support always-on operation. Built-in Windows apps and drivers run natively on Arm 64-bit processors, but 32-bit x86 apps require emulation, and 64-bit apps don’t run at all.

The x86 emulator translates instruction blocks into the Arm equivalent and, in the process, applies performance optimizations. To reduce translation overhead, an OS service caches the translated code so it’s available the next time the app runs. Nevertheless, reviewers of Snapdragon 835–based ACPCs have reported significant slowdowns for emulated apps.

The Snapdragon 850 platform will boost performance compared with first-generation Snapdragon 835 PCs, but it won’t address the poor emulation performance. To really level the playing field, Microsoft must convince more developers to compile their apps for Arm. Just as the need to run an emulator made it difficult for MIPS and x86 processors to compete with Arm-based smartphones, the biggest challenge facing Windows on Arm is the lack of compatible software.

Subscribers can view the full article in the Microprocessor Report.

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