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Xbox System Software Overview
- official leaked document from the XDK 
The system software of the Microsoft® Xbox® game system will
provide a small, fast, safe, robust, and customizable environment
to enable the creation of great games for the Xbox game system.
It will provide a set of useful common services to be taken advantage
of by game developers, such as networking and file system input/output,
so that developers can focus on creating great games. It will also
provide an attractive, easy-to-use interface for functions other
than running games, such as playing DVD movies or CD music or configuring
the Xbox console.
The Xbox system software will have these components:
* The Xbox read-only memory (ROM)
* The Xbox Dashboard
* The Xbox Title Libraries
Xbox Game System ROM
The ROM of the motherboard on the Xbox console will provide the
following system-software services:
* Hardware Abstraction Layer (HAL)
* Driver model
* Hard disk driver
* DVD driver
* FAT32 file system
* UDFS file system
* Copy-protection support
* Certificate/signature validation
* Basic application services such as the application loader, memory management, and threading
For more information about the design and functionality of the Xbox
software system, see the following topics:
* Software System Kernel
* Power Up
* Media Detection
* Game Launch
Software
System Kernel
The kernel is
based on Microsoft® Windows® 2000. Many features of Windows 2000 are not
included in the Xbox system software, including those related to running
on multiple hardware platforms or running multiple processes at once.
For more information about unsupported Microsoft® Win32® application programming
interfaces (APIs), see Win32 API (below).
There will be no support for code running in user mode (Ring 3) on the
Xbox game system. All code will execute in kernel mode (Ring 0). Only
one process runs at a time, and that process will support multiple threads.
There is no Windows 2000 desktop user interface; the user interface is
provided by the individual Xbox games or the Xbox Dashboard if no game
is running.
Power
Up
When the user turns on the console,
the system software is decompressed out of read-only memory (ROM) into
random access memory (RAM). Once in RAM, the system software initializes
the hardware (DVD, audio, video, and so on).
After the hardware has been initialized, the system software will display
the boot graphic and play the startup sound. Because there are no video
or audio drivers in the kernel, this is done by poking the registers of
the sound and video card directly. This graphic and sound will play approximately
1 second from the time the machine is turned on.
Media Detection
Upon power up and during the display of the startup graphic and the playing
of sound, the system software attempts to determine what type of media
is in the DVD drive. If it determines that the media is a game, it loads
the game into RAM, checks the signature of the game to verify that it
is an authentic copy, then starts playing the game. If the media is not
a game, the Xbox Dashboard is run as follows:
* Movies are played by the Xbox Dashboard video player.
* Audio CDs are played by the Xbox Dashboard audio player.
* If unsupported media is present, an invalid content message is shown
and the Xbox Dashboard game-system-configuration user interface runs.
* If no media is present, the Xbox Dashboard game-system-configuration
user interface runs.
For more information, see Xbox Dashboard (below).
Supported media are CD, DVD, CD-RW, or DVD-R. There is no CD-R support.
Game Launch
Once the system software has determined that the media contains an
Xbox game, it loads the game developer bitmaps, publisher bitmaps, license
bitmaps, and so on. These will be stored in a predetermined location on
the DVD, will contain no executable code, and will be identified with
a predefined schema. The system software will display these bitmaps sequentially,
after the boot graphic and sound have appeared, while the game itself
is being streamed from the DVD into RAM. As the game image is streamed
into memory, the system software checks the signatures of each section
of the image on the fly.
Once the game image is in memory, the system software will start the game.
At this point, the kernel is acting in conjunction with the Xbox Title
Libraries to provide all of the basic services for the game itself.
The Xbox game image format is not compatible with other executable systems,
such as Windows 2000 executable format. The Xbox game image must be loaded
by the Xbox system software application, loading utilities directly into
RAM in 64-megabyte (MB) blocks. Unlike standard Windows 2000 applications,
there are no dynamic-link library (DLL) loads, no fixups, and so on.
Xbox Title Libraries
The Xbox Title Libraries define the programming model used to develop
software for the Xbox game system. They consist of all APIs provided with
the Xbox Development Kit, which are linked into every title written for
the Xbox game system, including:
* Subset of the Microsoft Win32 APIs
* Subset of the Microsoft® DirectX® 8.0 APIs
* Xbox video driver
* Xbox audio driver
* Xbox universal serial bus (USB) driver
* Xbox modem driver
* Xbox memory unit support
* Xbox network stack: media access control (MAC), Network Driver
Interface Specification (NDIS), Transmission Control Protocol/Internet
Protocol (TCP/IP), Winsock
The primary programming model for the Xbox game system will be defined
by the Xbox Title Libraries. Because the Xbox Title Libraries are partitioned
into distinct libraries (modular), game developers can pick and choose
which libraries are appropriate for their title. For example, if a game
will support online play, they include the Xbox networking library with
their game. If no online play support is planned, they do not include
the Xbox networking library. While some support is implemented in the
kernel of the system software in the Xbox game system ROM (for example,
file system support, threading, memory management), the APIs to access
these features are exposed through the Xbox Title Libraries.
Note All Xbox-compatible code runs at Ring 0 on the Xbox game system,
which means the Xbox Title Libraries are implemented in kernel mode and
all games run in kernel mode. However, all Xbox Title Libraries will be
signature-compatible with their user-mode implementation. From a developer's
perspective, the Xbox Title Libraries function as they would in user mode.
Kernel mode results in faster performance at run time.
For more information about the components of the Xbox Title Libraries,
see the following topics:
* Win32 API
* Graphics
* Input
* Audio
* Video
* Networking
* New Xbox Services
Win32 API
A subset of the Win32 APIs is supported by the Xbox system software.
We are currently doing analysis to determine exactly which APIs will be
needed. Some omissions from the standard Win32 environment will include
portions of the User, Graphics Device Interface (GDI), OLE, or the Services
interfaces. Any APIs from User and GDI that are essential will be included
as needed.
Services from Windows 2000 not available in the Xbox system software include:
* Services
* Plug and play
* Additional hardware enumeration
* Hot docking
* All unsupported drivers
* Power management
* Virtual memory (paging)
* Multiple-process support
* Multiple-processor support
* Windows NT File System (NTFS)
Graphics
Microsoft® Direct3D® will be the primary graphics API for the Xbox
game system. Direct3D for the Xbox game system will be based on DirectX
8.0, and implemented using a custom driver specific to the final NVIDIA
chipset and video adapter. The graphics API for the Xbox game system is
compatible with DirectX at the API layer, while providing the thinnest,
fastest-possible access to the video hardware. The Direct3D driver is
combined with the HAL to create a completely monolithic driver implementation.
The drivers support both National Television System Committee (NTSC) and
Phase Alternating Line (PAL) TV output. Moving Picture Experts Group (MPEG)
video is supported.
Input
The Xbox controller connections and external peripheral connection are
USB ports with an Xbox proprietary connector. The Xbox game system implements
USB drivers for any possible peripherals connected to the Xbox console.
Only full-speed USB is supported.
An API specific to the Xbox game system, based on Microsoft® DirectInput®,
is used for development with most Xbox controllers. Xbox-licensed game
systems should work without an additional driver. This assumes that Xbox
consoles do not introduce any new axis or capability not covered by the
standard Xbox game system API.
Audio
The audio APIs for the Xbox game system are based on subsets of Microsoft®
DirectSound® and Microsoft® DirectMusic®, from DirectX 8.0. Audio streaming
will not be based on Microsoft® DirectShow®, however. Instead, an Xbox-specific
audio streaming API will be implemented for high quality CD playback without
skipping, and without undue CPU utilization. The following features are
supported by the Xbox audio APIs:
* WAV files
* MIDI playback
* Interactive music
* Microsoft Windows Media™ (WMA) files
* 3D sound
There is no support for Redbook audio or random instruments.
Video
Like audio streaming, the video streaming API for the Xbox game system
will not be based on DirectShow. Instead, an Xbox-specific video streaming
API will be implemented.
Networking
Xbox hardware includes two devices for online connectivity:
* Built-in Ethernet card for broadband: cable modems, digital subscriber
line (DSL) or local network
* Optional 56-kilobits per second (Kbps) modem peripheral for dial-up,
with a USB modem driver and dialer included in the Xbox Title Libraries
The Xbox Title Libraries include networking services for online capabilities.
Included with these will be TCP/IP and Winsock support. If online connectivity
is not wanted for a game, the Xbox networking libraries should not be
linked and included with the game title.
The API to access networking services is based on a subset of Microsoft®
DirectPlay® from DirectX 8.0. DirectPlay lobby or voice features will
not be supported, however.
New Xbox Services
The Xbox system software will include new services specific to the Xbox
game sytem and not based on any existing Win32 or DirectX APIs. New services
provided by the Xbox Title Libraries include:
* High-score publishing, including a common format to be shared online.
* Virtual keyboard support for simplified text entry and game-specific
skins.
* User identity that associates names, preferences, and statistics to
be shared online.
* Hard disk management to allow usage of the Xbox hard disk by game titles
for configuration stores, cache space, and so on.
Xbox Dashboard
The Xbox Dashboard is an application installed on the Xbox hard disk,
which essentially is the user interface when a game is not running in
the Xbox game system. The Xbox Dashboard provides the following services:
* DVD player
* CD player
* System configuration utilities for the Xbox game system
* Multiplayer and online connectivity utilities
* Saved game management
* Error handling
Initially, the user interface of the Xbox Dashboard offers the following
choices to the user:
* Play
* Configure
* Go online
* Manage games
DVD Player
This can be configured for AutoPlay (so that a DVD video will play
simply by inserting into the Xbox console and powering up) or for manual
control, which presents controls for pause, skip, and so on.
CD Player
This can be configured for AutoPlay (so that an audio CD will play
simply by inserting into the Xbox console and powering up) or for manual
control, which presents controls for pause, skip, playlist management,
and so on.
Xbox Game System Configuration
This presents the user interface for all preferences and settings
for the Xbox game system, including the following:
* Video configuration
* Audio configuration
* Parental control
* Date and time
Multiplayer and Online
This presents the user interface for all online connectivity, including
the following:
* Lobby browser
* Lobby favorites
* High score browser
* Xbox Zone browser
* Online sign-up and configuration
Saved Game Management
This presents the user interface for hard disk management, including
saving, deleting, and copying games between the Xbox hard disk and the
Xbox Zone (online).
Error Handling
Errors that occur during system-boot execution of the Xbox Dashboard will
be handled by the Xbox Dashboard. However, hardware errors (for example,
hard disk failure) will be handled by the Xbox system software. Game errors
also are not handled by the Xbox Dashboard, but by the game software itself.
Jason Brown, Web Editor, XBOX365
Thanks to
Darkman for his help in this story
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