
		Documentation for Enabling and Using Multihead on PowerStorm 4D10T

					Version 2.0b
					05/21/98


The PowerStorm 4D10T driver supports Multihead on both Alpha and Intel Platforms. This document  describes the supported configurations on Alpha and Intel Platforms, how to enable Multihead, recommendations on use of Multihead, and known restrictions. With the introduction of V2.0 drivers, 3D HW acceleration is supported on certain Multihead configurations. This document also describes 3D HW acceleration in Multihead configurations, recommendations on how to use it and known restrictions. 

Please read the entire document before planning to use the PowerStorm 4D10T driver in a Multihead configuration. 

1.0 What is Multihead ?

The Windows NT 4.0 graphics interface, GDI, does not handle the use of multiple graphics boards. It is left as a task for the display drivers to adapt a customized setup that creates a virtual window spanning multiple screens, with each screen connected to its own graphics board. This is commonly known as Multihead (also known as Multimonitor).

The PowerStorm 4D10T driver contains the necessary code to support Multihead configurations. The driver can accelerate GDI calls (2D Multihead) as well as OpenGL calls (3D Multihead) in Multihead configurations. In the current implementation, only Homogeneous Multihead is supported. Homogeneous Multihead refers to support of configurations containing identical devices. For example, Multihead will function correctly in a system containing multiple 8MB PowerStorm 4D10T's, however, it will not function correctly in a system containing a mixture of 4MB and 8MB PowerStorm 4D10T's or in a system containing a PowerStorm 4D30T and 4D10T.

2.0 Supported Configurations for 2D Multihead

The different configurations supported for 2D Multihead on Alpha and Intel platforms are listed below. 

Alpha Platforms The Digital Personal Workstation Series line of systems (500a, 500au) that use PowerStorm 4D10T can support 2D Multihead, up to 3 4MB or 3 8MB PowerStorm 4D10T's. 

Intel Platforms The Digital Personal Workstation Series line of systems (300i, 300i+, etc.) that use PowerStorm 4D10T can support 2D Multihead, up to 3  4MB or 3 8MB PowerStrom 4D10T's.


3.0 How to enable 2D Multihead

This section assumes that you have a working system with one PowerStorm 4D10T. To enable Multihead:

- Shut the system down and turn  the power off.
- Disable VGA on all the PowerStorm 4D10T cards except the one which will be the VGA console. The Multihead system should contain only one PowerStorm 4D10T card with VGA enabled. Note: To disable VGA, move the jumper on the PowerStorm 4D10T to cover pins 2-3. To enable VGA, move the jumper on the PowerStorm 4D10T to cover pins 1-2. 
	- Plug in all the cards into the system. Connect the monitors to all the cards.
- Power on the system. Power on the monitors.

The monitor connected to PowerStorm 4D10T with VGA enabled will display the boot process. It is very likely that once the system boots into Graphics mode, the login box will be on a different monitor. It is very important to power on all the monitors and make sure they are connected to their respective cards properly.

On login, go to Display Properties (either by right-clicking your mouse on the desktop or from the Control Panel). Select settings and modify the resolution. You will be able to select resolutions that span multiple screens. Select a suitable resolution for your system configuration and apply the change after testing it. At this point, the different monitors should reveal parts of a large Desktop. You should be able to run 2D applications, move them from one window to another, and maximize the application windows to cover the different monitors. 

If on login, you are not able to modify the resolution to cover multiple monitors, please check the following:

- Are all the PowerStorm 4D10T's plugged in properly ?
- Is VGA disabled on all but one PowerStorm 4D10T's ?
 
4.0 Known Restrictions for 2D Multihead

a) Digital Personal Workstation (DPW) 300i series systems contain an onboard Permedia P2 chip. This is the same chipset used by the PowerStorm 4D10T. This allows multihead configurations that can be a combination of PowerStorm 4D10Ts and the onboard Permedia P2.  

When a PowerStorm 4D10T is plugged into a DPW 300i series workstation with VGA enabled, the onboard Permedia P2 is disabled. This results in a single head configuration.

If a PowerStorm 4D10T is plugged into a DPW 300i series workstation with VGA disabled, the onboard Permedia P2 is enabled and acts as the VGA console. This results in a Multihead configuration. Note: It is important to make sure that onboard Permedia P2 has similar memory configuration as the PowerStorm 4D10T - e.g. both should have either 4MB or 8MB.

The following are known restrictions in supporting Multihead on DPW 300i series systems:

- Up to 3 heads are supported at the same time on DPW 300i series systems. All 3 heads need to be PowerStorm 4D10Ts (onboard Permedia P2 can not be used in this setup).

- Manually enabling the VGA on the onboard Permedia P2 using the BIOS will cause display corruption on the onboard head in a Multihead configuration.

5.0 3D HW Acceleration in Multihead Configurations

With the introduction of PowerStorm 4D10T V2.0 drivers, 3D Multihead is now supported in certain configurations. 3D Multihead refers to HW acceleration of OpenGL in Multihead configurations. Prior to V2.0, applications using OpenGL API would work but would use the Microsoft OpenGL Software Path thus resulting in slow performance. With the current implementation, applications using OpenGL API would go through HW acceleration as long as:

- HW acceleration is supported for that Visual Mode (e.g. 1024x768 @16bit color @60hz).
- The application window size is less than the screen size (e.g. 1024x768).

Applications can be dragged from one monitor screen to another without loss in performance. 

6.0 Supported Configurations for 3D Multihead

The different configurations supported for 3D Multihead on Alpha and Intel platforms are listed below. 

Alpha Platforms The Digital Personal Workstation Series line of systems (500a, 500au) that use PowerStorm 4D10T can support 3D Multihead, up to 3 4MB or 3 8MB PowerStorm 4D10T's.

Intel Platforms 3D Multihead is currently not supported on Intel Platforms.
		
7.0 Known Restrictions for 3D Multihead 

Maximizing the OpenGL application window to cover multiple monitor screens will force the application to use Microsoft OpenGL Software Path. Resizing  the application would still force the application to use the Software Path. Exting from the application and re-running it will enable HW acceleration again.

8.0 Optimal use of Multihead while running Applications

TBD

