Exactly - that is the (one and only) point I was making in the comment to which you have been responding.Clearly one can't jump forward past the live transmission point.
Indeed. Even Sky boxes etc. do that. however, again, one obviously cannot 'look forward' to something that has not yet been broadcast/recorded - so, if one starts watching (virtually) at the start of the broadcast, one cannot 'look forward' unless one first pauses the replay/viewing for a while.With Myth even watching live TV is done by recording the stream and watching the recording - and I suspect that's the case with other PVR systems.
Yes, on reflection you're right. With the vast amounts of memory (in and/or outside the HDD now available, even if one has multiple processes running which 'simultaneously' need to interact with (read and/or write) several physically remote parts of the disk(s), the head(s) probably don't need to move around more than once a second or so, if that.Yes, buffering is the key - but typically not as much as you might think.
[ Somewhat extending this, and moving away from video recording to computing in general, the vast amounts of RAM now available means that it often makes sense to read an entire file from disk into RAM and undertake reading and modifications/manipulations of that file in RAM before eventually writing it back to disk - rather than attempting to use the file 'in situ' on the disk. I regularly do this with large (up to 'a few hundred MB') data/database files. ]
Sure, but that's almost semantic, being just one aspect of 'buffering'.There is also the option of readahead. Many drives do this internally - you read one block, the drive reads the next few and holds them in RAM ready for the system to read them. The system can also do that.
Quite so. As I wrote above ...If you think about it, anything involving disk i/o must involve some buffering since modern disks all have a sector size of 4k ....
Yes, I presume that the answer has to be in buffering. Indeed, there obviously has to be some (whether internal and/or external to the HDD), otherwise it often just wouldn't work (sensibly) at all. Indeed, I suspect that even the "50 IO operations per second" mentioned by plugwash probably relies upon (I assume 'internal') buffering, because ....
That is, of course, the key to all this (to which I hadn't initially given enough thought) - and not just within the drives, but external to the drives as well.Most modern drives have huge amounts of RAM - many times what I had in my first computer.
In terms of your "many times" (what you had in your first computer), I may have to investigate whether the Guinness Book of Records has a category for "extreme understatements" The gods are being kind to me today, in making the arithmetic easy, since my first computer had 8 kB of RAM, whereas the one on which I'm writing this message has 8 GB - so, in my case, that "many times" becomes "1,000,000 times" (which I guess we can probably agree is "many" ). [... and, in passing, not much less in terms of HDD capacity - my first one was 5 MB, and the one I'm using here is 2 TB {and could easily be 4 TB} - hence "400,000 times" {or "800,000 times" if it were 4 TB} ].
The increasing amount of memory (both within and outside of drives) has been astronomical, rapid and more-or-less exponential. That makes me wonder to what extent the 'early' implementations (of video recording/replaying) we're talking about were somewhat 'struggling' not that many years ago?
Kind Regards, John