The JVC GY-HM170 supports an SDXC memory card which is better than the SDHC memory card supported by most video cameras that have been available for more than a year. SDXC cards are SD cards but with a much higher capacity and faster processing speeds. They have a maximum capacity of 2TB (Terabytes).
An SDXC memory card is actually the best supported memory card type amongst all big sensor size video cameras that have been available for around the same time as the GY-HM170.
The worst supported memory card type amongst comparable types of video camera is SD.
SDHC cards are DS cards with a higher capacity of up to 32GB.