As technology improves, HMDs are becoming less bulky. More than 17 are currently on the market. LCD technology is one of the two current display options for HMDs. LCDs in VR are mini versions of the screens you see on portable computers, game systems, and digital watches. When the actions of a VR user's virtual agent occur simultaneously with those of the VR user, that is real time.
Real time is desired.
Lag can make you sick. If you raise your real hand, you see your virtual agent's hand raise in the VR world. The virtual environment that the VR user perceives. VR data base. You cannot build a VR environment without a data base.