This goes back to the 50X days when the HDD's did not spin down. Dish had high HDD failure rates (for them anyway) and good ol' Dave Kummer had explained that the 50X (the only DVR's available in those days) would spin down shortly after being put in standby to increase life of the HDD.
From the 721 and subsequent DVR's, the HDD was/is always spinning, and never to spin down along with not recording to buffer unless it was a timer recording. I think this is just a case of legacy "thinking" or "that's how the HDD/buffer has been handled for about a decade; there is no reason to change the software or manner of buffer in standby when there seem to be far more important features customers demand," sort of thinking. While the HDD is surely spinning, one could argue that the slider and arms involved in writing to the HDD are given a good rest from constantly, never ceasing to write as this is what can shorten the life of an HDD, especially writing from two + tuners 24/7, this has a hand in decreasing HDD life even further. In past Tech Forum some years ago, Mark Jackson confirmed they had a prototype multiple tuner DVR (more than 2), and they were experiencing very high failure rate of the HDD's. However, today, HDD's seem bee able to survive being beat up by 3 live HD streams, 1 download occuring, and multiple playback of content to different clients, and DirecTV's 5 tuner DVR seems to say something for today HDD's. But I would be willing to say that the 5 tuner DVR's HDD is NOT going to last as long as some would expect compared to a 2 tuner DVR.
Yes, TiVo constantly buffers and spins, but this would also seem to allow for the most reliable experience for TiVo's multi-room viewing (S2 & S3) and streaming (S4) features: always fully alive and active arms and writers when accessing that DVR from another room.
Bottom line, there may be technical reasons to always buffer (making it EASIER or MORE RELIABLE for specific feature) or a consequence or just plain a preference, for whatever reason. Of course, during any recording, Dish DVR's also record the other tuner to the buffer.
On occasion, it was nice that my TiVo had been buffering (only a 30 minute buffer on TiVo), but most often it either wasn't enough of a buffer to catch the entire program or it was tuned to a channel I didn't want buffered. So, it really isn't such "feature" after all. It couldn't automatically re-tune to the channels I would always like buffered. That would be a record timer, the same solution for a Dish DVR, and TiVo does not tout the constant buffering as anything at all. We TiVo owners would take an hour on the buffer, even if it stopped buffering in standby. IMHO, this buffering in standby is a "whatever" function that, one would think, is nowhere near a make or break function. I would think that Manual Timers, DishPass, OTA recording and guide info support, saving our preferences and timers in the cloud, much better interface and browsing for on-line content (it is a DISASTER now), and even a 4th tuner on the Hopper would be real features that would enhance the Hopper/Joey system more than any buffering in standby. Buffering in standby would be fine after perfecting things. Of course, a buffer in standby software update would surely mess-up some other higher and more important feature as a consequence of Dish's software updates
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