Good tip, Pepper. Got my curiosity up and found the drive is on the "approved" list for:
501/508 - Reports as 510 afterwards
5100/5800 - Reports as 5900 afterwards
Also approved for 522/625/942/9200.
Got this info from some "group" of "yahoos"... Never tried any of this myself.
seems like there was a thread or two around here about how having an extra 4R120L0 or two around could come in quite handy for the owner of one or more 522s. hint: this was long before "EHD" support was made available for ViP DVRs.