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 20-30 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 antialiasing? Not a problem for the Xbox 360. “
 (From hardware.teamxbox.com)
Dedicated Operating Systems

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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
 http://domino.watson.ibm.com/comm/research.nsf/
pages/r.arch.simd.html
The Xenon (PowerPC)
 http://en.wikipedia.org/wiki/Xenon_(processor)
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
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Windows NT (3.51 and 4.0)
Mac OS X up to 10.5.8
Solaris 2.5.1 (PowerPC edition)
Amiga OS4
Free60 – porting BSD, Linux and other systems
to the 360
 Embedded & Special Purpose
 Cisco IOS
 WII (“Broadway”)
Questions?