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article imageMicrosoft reveals HoloLens' secret 24-core custom processor

By James Walker     Aug 23, 2016 in Technology
Microsoft has publicly revealed details of the custom-built processor that powers the holographic processor inside the HoloLens. A 24-core chip accompanies the main system processor to make the holographic display possible. It's both powerful and pricey.
HoloLens has two processors. The main CPU is an Intel chip that has been documented since Microsoft launched the first developers edition of the HoloLens back in February. This is accompanied by a separate Holographic Processing Unit (HPU) box that has been shrouded in mystery over the past few months.
Yesterday, Microsoft revealed what's inside the HPU. As reported by The Register, it detailed the unique processing box at the Hot Chips conference yesterday. The mysterious HPU contains a custom-built 28nm processor that works with the main Intel chip to power the holographic display, primarily taking responsibility for sensor processing.
The processor is built by TSMC and has 24 distinct cores. It is joined by 1GB of low-power DDR3 RAM and is capable of performing a trillion calculations every second. When running HoloLens' complex algorithms, it is over 200 times faster than the Intel CPU alone. Despite the high performance, the entire HPU draws just 10W of power from the wall.
The extremely high performance of the HPU is necessary because of the workload it's tasked with. It handles all of the environmental sensor processing for the HoloLens, aggregating data from the sensors on the outside of the wearer. It then considers input controls, such as gestures, and the HoloLens' environmental sensing features. Each of the 24 cores has its own assigned task to work on.
Needless to say, this isn't your standard processor. Microsoft has worked directly with TSMC to design the chip for the specific demands of the HoloLens. This is why it acts as a co-processor rather than running the entire device. It isn't capable of supporting the HoloLens' operating system. It's purely a computational machine, crunching through calculations at an otherwise impossible rate.
The main processor is a 14nm Intel Atom x86 Cherry Trail chip with its own 1GB of RAM. It's not a high-performance CPU and is akin to the low-power chips found in budget laptops and tablets. It's good enough to run Windows 10 and Universal Windows Apps, however. It hands off to the HPU when it needs to access sensor values.
The bespoke nature of the HPU is likely to become an issue when trying to reduce costs of the HoloLens and begin selling it to consumers. Microsoft has extensively modified the TSMC chip it's based on, going so far as to add its own instructions to optimise holographic calculations. The hardware could become more standardised over the next few years, however. As more headsets hit the market, it's likely they'll all start demanding a common set of processing features that chip manufacturers will be able to bake into their products.
HoloLens began shipping to developers in March. It is now available to buy without pre-ordering from the HoloLens website, making it easier for developers to get started building holographic apps.
Next year, the Windows Holographic platform will be delivered to every Windows 10 PC, allowing you to use these apps on a headset powered by your existing devices. HoloLens is currently the only supported headset, although third-party products such as Intel's Project Alloy are expected to arrive in the next year.
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