OS Case Study: The Xbox 360  Instructor: Rob Nash  Readings: See citations in the slides

Where We’re At & Where We’re Going  Today:  A new guest Operating System  Performance analysis of Windows on a multi- core architecture  Nifty new tools in VS 2010  A Segment on Memory Management  Last minutes will be dedicated to the lab

Xbox V1.0 – A Brief History  Xbox = DirectX Box  The first Xbox was made with standard PC parts  The second follows this tradition, but alters the platform

Xbox V2.0 with the PPC(Xenon)

First, a Plug…  “The Xbox 360 represents a technological breakthrough only possible because of the hard work of hundreds of masterminds around the world who converged to create the ultimate gaming machine. Unreal Engine 3-powered games running at 1280x720 with full screen anti- aliasing? Not a problem for the Xbox 360. “  (From hardware.teamxbox.com)

Dedicated Operating Systems  Designed with a specific set of goals  DirectX Box OS is a lightweight wrapper for Direct3D calls and basic resource management  What are the resources here?  The graphics card + shader pipeline  DVD optical drive  Main memory (shared)  6 hardware-supported threads  Optional removable HD  Many APIs from Win32 are seen in Xbox code  CreateThread, WaitForSingleObject  Graphics handled through a variation of Direct3D  Not much HAL here – usually direct communication with the graphics hardware  Microsoft worked with IBM, ATI, and Silicon Integrated Systems to develop the hardware

Architectural Summary  3 Core PowerPC, 3.2 Ghz  Each is symmetric (SMT), so 2 HW threads per core  512 MB of GDDR3 RAM (integrated)  700 Mhz DDR bus  ATI graphics (roughly ATI radeon X1950)  SIMD

A SIMD Aside  “As the name suggests, SIMD processing increases the work a single instruction performs so that it operates on multiple data items simultaneously. “  I.e. “short vector” processing for graphics (2,3,and 4D)  Why 4D?  See IBM’s site for more information  pages/r.arch.simd.html

The Xenon (PowerPC) 

The Custom ATI GPU  500 MHz GPU  Unified shader architecture  48-way parallel shader pipelines  48 billion shader ops per sec  10MB Dedicated frame buffer  Poly Count  500 million triangles per sec  4x MSAA

Memory Subsystem  Memory Interface bus bandwidth: 22.4GB/s  Front-side bus: 21.6GB/s  Memory references use inverted page tables  Respectable transfer rates, but offers no new solutions to the CPU/Memory speed gap  Caches  Streaming data

Cross-Cutting OS Issues  What is the responsibility of this OS?  i.e. What is this hardware supposed to accomplish?  What languages are supported?  What tools are offered?  How portable are the applications?

Compiler and Language Support  C/C++ still the leading language due to speed and legacy  Recent support was added to the kernel for managed code (C#)  Effectively used in XNA  Still some scalability & GC issues  Visual Studio offers a tightly integrated IDE

A Thin OS  16MB for the entire OS  Compare this to even the graphics card frame buffer!  10MB  Has access to 32MB for OS operations

The Audio Subsystem  Multichannel surround sound  48 KHZ 16-bit audio  32-bit processiong  More than 256 audio channels

Extending the OS…  MS uses network and disk updates for its OS  The “dashboard” is the user’s interface  Updated frequently  Custom design for the OS primarily centers around device drivers

Imagine G5s Lining the Walls..  “From a hardware point of view the Xbox 360 represents an evolution from the Xbox, but when you see the new console as part of a whole platform, the Xbox 360 represents a true REVOLUTION. “  An odd site at Microsoft, but this was our platform and architecture.

Alternate OS – Same Architecture  Windows NT (3.51 and 4.0)  Mac OS X up to  Solaris (PowerPC edition)  Amiga OS4  Free60 – porting BSD, Linux and other systems to the 360  Embedded & Special Purpose  Cisco IOS  WII (“Broadway”)

Questions?