A major improvement, pioneered by NEC, led to the first practical LCD televisions. NEC noticed that liquid crystals take some time to start moving into their new orientation, but stop rapidly. If the initial movement could be accelerated, the overall performance would be increased. NEC's solution was to boost the voltage during the "spin up period" when the capacitor is initially being charged, and then dropping back to normal levels to fill it to the required voltage. A common method is to double the voltage, but halve the pulse width, delivering the same total amount of power. Named "Overdrive" by NEC, the technique is now widely used on almost all LCDs.
Another major improvement in response time was achieved by adding memory to hold the contents of the display – something that a television needs to do anyway, but was not originally required in the computer monitor role that bootstrapped the LCD industry. In older displays the active matrix capacitors were first drained, and then recharged to the new value with every refresh. But in most cases, the vast majority of the screen's image does not change from frame to frame. By holding the before and after values in computer memory, comparing them, and only resetting those sub-pixels that actually changed, the amount of time spent charging and discharging the capacitors was reduced. Moreover the capacitors are not drained completely; instead, their existing charge level is either increased or decreased to match the new value, which typically requires fewer charging pulses. This change, which was isolated to the driver electronics and inexpensive to implement, improved response times by about two times. Sony HDR-CX160
Together, along with continued improvements in the liquid crystals themselves, and by increasing refresh rates from 60 Hz to 120 and 240 Hz, response times fell from 20 ms in 2000 to about 2 ms in the best modern displays. But even this is not really fast enough because the pixel will still be switching while the frame is being displayed. Conventional CRTs are well under 1 ms, and plasma and OLED displays boast times on the order of 0.001 ms.