Basically, there are 3 types of USB KVM switch technologies in the market now.
1. Enumerated USB switch (hub structure, simple and cheap)
2. Emulated USB switch (hot-key control, but bad in compatibility)
3. Full DDM (Dynamic Device Mapping) USB switch, (best, hot-key control, no USB enumeration required, fastest switching, no compatibility issue, but expensive)
Google "USB DDM KVM switch", you can find more information.