"ProTools" (as in the ProTools mentioned by famous artists/producers in interviews) is a series of hardware DSP cards installed *inside* a computer which does all mixing, routing, effects, dynamics, etc. The computer is basically left to redraw the screen and if necessary, run host-based plugins (which, since it's doing nothing else, can run way more and run them more efficiently). Because hardware is doing all the work (like a RADAR, Akai DR-series, Roland VS-series, Alesis HD24, etc.), latency and buffers are a non-issue. The right PT|HD rig can play back 192 tracks of audio and mix them along with 96 simultaneous inputs... with a ton of world-class effects... with unnoticable latency. It acts, responds, and feels like hardware because it is hardware. Conversely, host-based solutions such as Cubase, Nuendo, Sonar, Logic, and even PTLE feel like you're using a computer. There is no comparison, power-wise, unless you want to compare it to something like Ensoniq's long-dead PARIS system (also DSP-based), which was fantastic. Note that since ProTools is hardware, you don't have to use ProTools software (tho' it's included). For example, I use Logic Pro as a front end. Same TDM plugins, same track and input count, same negligible latency, same stability, same routing flexibility... Only with Logic painted on top. Digital Performer also can act as a software front end for ProTools, as could BIAS Peak on OS9. That said, the ProTools software is excellent, but it is NOT what makes "ProTools" ProTools. I'll have to copy this as a text file because this question seems to pop up every few days.
