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Video and GUI
1. Basics
The most important things about speeding up your existing video card are resolution, colour depth and a good display driver. Importance of each factor varies depending on the age of your video card. Essentially, the higher the number of pixels the video card is asked to display, the more time and computer power will be required. Beginning with cards of the Matrox G400's generation this factor can be neglected most the time. Therefore, if you own an older card and you can live with 800 x 600 resolution, then that would be a better performance choice than opting for 1024 x 768, or higher. Also, the less colors in your display palette, the faster your video response time will be. If you don't need 16.7 million colors (24 or 32 bit colour depth), don't use them. 65335 colours or 16bit colour depth will be displayed faster and your eyes won't note the difference.
Alas, there are very few companies left that make decent OS/2 drivers for their graphics cards. In fact Matrox is the only one since ELSA left the OS/2 market. Add to this that nowadays the driver has become the biggest issue as far as speed is concerned (my Matrox G400 is pretty much equally fast at 800x600 and 1600x1200 resolutions), which makes it even more annoying. BUT in 1999 Scitech Soft began porting their Display Doctor to OS/2! This software provides highly accelerated plug&play drivers for most graphics cards or chip sets on earth and also adds things like customizable screen modes. According to Sysbench (a benchmarking suite for OS/2) a Matrox G400 achieves nearly double the performance as with the Matrox drivers. This driver is a commercial product that currently is still in beta stage, but already widely used. IBM licensed a "lite" version of this driver that is available to all OS/2 customers with a Software Choice subscription and all eComStation customers. This version has limited available modes and refresh rates (max. 85Hz).
2. DIVE performance
The following chapter is only relevant if your CPU belongs to the following families: AMD K6-2 or K6-III CPU with CXT core, AMD K7 (Athlon and Duron); Intel Pentium Pro, Pentium II, Celeron, and Pentium III.
These processors offer features called write allocation and write combining. They can speed up data transfer to the video memory and general memory write operations consideringly, but they need to be turned on. Unfortunately, many BIOSes won't do that for you and it has to be done by a driver instead. To my knowledge this feature is built into every Windows video driver, but for OS/2 Scitech Display Doctor is the only one that is capable of doing so. But only for a single processor.
But you are not completely out of luck if you don't have SDD installed or run an SMP machine. Several people
have written small drivers to switch on the features. For AMD K6-2 and K6-III processors I recommened the free
package setup4k6 by Cornel Huth that includes
a nice tool that comes in very handy for calculating the parameters that have to be passed to the driver. The
problem is that you have to specify the starting address of your video card's frame buffer. I was told that
it's easy to find it for any Matrox card, since the Matrox driver's settings tool displays it as Board
mapping on the Information tab. This is often wrong! Do not use that value.
Get the free tool DIVETEST instead. Start it, go to the DIVE tab
and press Query Caps. Now you should be able to see the required address in the Starts at: field
below the Get Framebuffer Information line. Use this address to calculate the required parameters. Doing
so increased DIVE-marks for my G400 in Sysbench from 80.613 to 117.665 which is the same value that can be achieved
with SDD. There is still one caveat: Do not activate EnDIVE, otherwise you will see a performance hit. But since
EnDIVE implementations don't work correctly for most video cards anyway, you probably won't loose any
features.
The recommened package for owners of Intel and AMD K7 processors is P6K7MTRR by Takayuki Suwa that is also capable of automatically setting up all processors of an SMP machine and provides an API for developers. The package includes a tool to determine the frame buffer address.
3. Bitmaps and pointers
Also related to video in OS/2 are bitmapped backgrounds. They may look very pretty on your Desktop, but they are stealing processing power and RAM from your computer. A background bitmap for the desktop with 256 colors requires about 3MB at a resolution of 1280x1024. Using color schemes that use colors from the mixed color palette will take more time to display than colors in the solid palette. This effect can be neglected for today's machines.
Remember that mouse pointers are bitmaps, too. So depending on the pointer's style and size different amounts of memory are used. The best is to stick to the default black and white pointers. This will also prevent slowdown and flickering that occur with DIVE programs otherwise. Also turn off the comet cursor since it consumes additional memory and processing power.
4. WPS stuff 
Keep the number of open windows to a minimum. Minimize or close windows that are not necessary, and your screen will refresh faster. Folders that use a "flowed format" will display their icons faster than the standard "non-grid format". This can be changed on the view page of the settings notebook. Also, stick to an 8-point (Warp 3) normal text font for maximum display speed.
Turning off the Desktop animation will also improve your video speed. Do a right-click on the Desktop to bring up the Desktop menu, and select System Setup. Find the System icon and double-click on it. Now click on the Window tab, and disable the animation feature.
Another tip regards the pop-up menu you see when you do a right-click with your mouse. If you know how to move, copy, create a shadow, find, etc., then seeing these options quickly becomes an annoyance. To get rid of these redundant items in Warp 3, add the line SET MENUSTYLE=SHORT to your CONFIG.SYS file and reboot or use XFolder's features to display only the items you want. If you have Warp 4 open the System object, go to the Menu tab and select short menus. There you can also de-select menu bars for folders to save some screen space since all items are included in the context menu anyway.
When you apply changes to a folder's content the system will automatically update the folder view. This can take some time if you have folders with lots of objects, especially if the option Always maintain sort order is activated or/and you are using detailed view. By adding the line SET AUTOREFRESHFOLDERS=NO to your CONFIG.SYS this feature can be turned off. Note however that you will have to close and re-open the folder or select Refresh now from the folder's context menu to have the folder reflect the changes.
5. Screensavers 
The one catch-word that everyone seems to connect with computer video is "screen-saver". OS/2 has a built-in one that you can activate on the Lock-up page of the Desktop settings notebook. It has several options, among them the options for a timed lock-up, and to lock-up your Desktop at startup. Both of these are a bad idea from a memory consumption point of view. Activating these options won't slow down your video processes as much as they will affect OS/2 memory use. The timed lock-up feature steals working memory away from OS/2, which will slow down all your processes. Turning the lock-up at startup feature on will give the computer more program code to crunch through at boot time. Not the end of the world, but still a slowdown. Basically, if you want to lock-up your computer, you are better off doing it manually from the launchpad, or the pop-up menu.
6. Video BIOS
One last thing that affects video speed is copying video routines from slow ROM to fast RAM. This is also referred to as shadow RAM. On most machines, if you hit the DEL key at boot-up time, then you will have access to the BIOS setup screens. Somewhere in there will be references to shadowing video and system ROM. When you find these items, make sure to turn them off. Yes, that's right, I said OFF. The simple reason is that OS/2 has built-in mechanisms to do the same thing as the shadow RAM does. If you don't turn the BIOS shadow RAM off, then you are effectively slowing down the computer by asking it to do things twice. To make matters worse, shadow RAM will take away from the RAM available to OS/2.