FLS = Fiber Local Storage. It’s not really necessary to know what it means (I don’t) but only to understand that in MS Windows there are a maximum of 128 FLS Slots per process, and with respect to this discussion, Cubase takes up some slots itself then each unique plugin (VSTi or FX) can take up one or more slots within the Cubase process as well. Therefore there is a hard limit to the number of unique plugins that you can utilise in Cubase. I say ‘unique’ plugins because only the first instance of any plugin takes up the slots, after that you can use that same plugin as many times as you like.
I have problems because I have quite a large collection of plugins which I like to use within all my project (e.g. UAD, Soundtoys bundle, Arturia bundle, etc.).
It’s not one plugin per slot because some plugins take more than one slot, and the worst one I’ve found is Arturia AnalogLab2 which will take up 28 slots. Waves is the best for me because it takes up only 2 slots ever no matter how many plugins I use.
The 128 limit was designed by MicroSoft and it’s been there for many years. It looks very unlikely it’ll change so it’s down to the software developers to find ways around the problem. I personally think it’s only really come to light recently because Steinberg have dropped the 32bit bridge and therefore all plugins now take up slots on the main Cubase process as opposed to say 1/2 the plugins taking slots in the 32bitBridge process (at least, that’s what I’m seeing in my setup).
It effects every DAW not just Steinberg, and Steinberg have recently reduced the number of slots Cubase takes for itself so they’re being pro-active in trying to help the situation. They say this is done by dynamically linking the DLLs instead of statically linking them. Plugin manufacturers can do this as well, and some are doing this faster than others.
Hopefully the more noise about this subject then the more the developers will streamline their software in future updates to help avoid the limit.