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Is there a way to remove Visual Themes from all applications as if the were running in Compatibility Mode?

[JedMeister]

I'm not 100% about what Visual Themes are disabled in compatibility mode as I don't use it so I'm only guessing what your after. I could be off in the wrong direction but here goes:

You can set XP to use the classic theme though display properties: Right-click on blank area on desktop>Properties>Theme tab (should be first one)>Windows Classic. You can also set screen resolution and colour depth there too (Settings tab). As for visual options I think they are turned off by default in Windows Classic theme but if not then right-click My Computer>Properties>Advanced tab>Performance settings>adjust for best performance

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Thank you for taking the time to reply JedMeister
I want to remove the classic theme as well. If you right click an application's icon, select Properties, click the Compatibility tab, click to check the Disable Visual Themes box, click OK and start the application you'll see what I mean. When running in safe mode Visual Themes are turned off as well.
I've got a couple of old PCs that I want to make use of but they are quite slow. I've sped them up a bit by turning off unnecessary services and using light weight applications and I want to try and squeeze a touch more speed out of them

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sc stop themes
sc config themes start= disabled

that should stop the themes service from starting. if it doesnt look exactly like compatibility mode(cant tell -im not near an XP box), keep in mind the options on compatibility tab are designed to trick the program into running on a newer version of windows than it was intended for and likely have more overhead than benefits and for that reason should not be used as tweaks.

if your just trying to get xp to run well on older hardware and have adequate security on your network youll see the largest performance gains from disabling system restore, security center, windows firewall, auto updates, windows file protection, remote registry, telephony, print spooler, etc and enabling them only when needed.