I personally use no less than 40% free space. NEVER completely fill up that hard drive or partition! Some folks recommend 20% free space.some higher. Always remember you need a certain percentage of 'free space' remaining on your FSX drive for file transfers, etc. IF your transfer speeds are OK, then you don't have to put the addon on the same drive as FSX.4. It depends on how FSX 'interacts' with them, and if your computer is fast enough to handle transfers of information, like weather updates, between your hard drives. Some utility addons like weather generators MAY or may NOT need to go on the same drive as FSX. CAVEAT: If running the addon ADDS MORE textures, etc, to FSX, then you need to add the increased size of those extra textures, etc, added to FSX to your 'space requirements' calculation.but NOT the entire addon itself.3. If the addon just REPLACES textures, etc, in FSX, without making a Scenery Library entry, it does NOT have to go on the same drive as FSX. If the addon makes a Scenery Library entry, then it should go on the same drive as FSX.2. Here is a 'generic' list of things to consider:1. They could be installed on an external hard drive, the interface run to replace the FSX textures, then FSX runs without accesssing anything in the GEX or FEX installations during your FSX session. There is no reason whatsoever to have to install GEX or FEX on the same drive as FSX.

They replace textures in FSX from an external interface you run PRIOR to running FSX. The size of these programs should be considered when determining hard drive space requirements.Other programs are NOT accessed 'real time' while FSX is running. The same applies to an addon like an aircraft, or any addon that makes a Scenery Library entry in FSX. The amount of space 'required' on the FSX drive should be calculated by the size of the addons FSX actually accesses in 'real time' while running FSX.For instance, UTX needs to be installed IN the FSX directory, and FSX will use the files in UTX while running.

Some folks are missing an important point here.

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