Grounding an Appliance

[JohnW2]

Clearly one can't jump forward past the live transmission point.

Exactly - that is the (one and only) point I was making in the comment to which you have been responding.

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.

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.

Yes, buffering is the key - but typically not as much as you might think.

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.

[ 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. ]

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.

Sure, but that's almost semantic, being just one aspect of 'buffering'.

If you think about it, anything involving disk i/o must involve some buffering since modern disks all have a sector size of 4k ....

Quite so. As I wrote above ...

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 ....

Most modern drives have huge amounts of RAM - many times what I had in my first computer.

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.

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

 

[Harry Bloomfield]

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?

Likewise the cost of memory and HDD's too. My first HDD, bought as a second hand item, had new cost a few £thousands, was massive, needed very careful handling and by comparison desperately slow. Tiny, modern TB drives can now be had for £26 and can be slipped in a shirt pocket.

 

[JohnW2]

Likewise the cost of memory and HDD's too. My first HDD, bought as a second hand item, had new cost a few £thousands, was massive, needed very careful handling and by comparison desperately slow. Tiny, modern TB drives can now be had for £26 and can be slipped in a shirt pocket.

Quite so. I recall buying 32 kB's worth of LSI dynamic memory chips in (at a guess) the late 70s for well over £100 - probably approaching a month's worth of my income up the time. I also recall subsequently 'upgrading' my initial 5 MB HDD to a 10 MB one for a price in an effectively comparable ballpark to that.

Kind Regards, John

 

[JohnW2]

Quite so. I recall buying 32 kB's worth of LSI dynamic memory chips in (at a guess) the late 70s for well over £100 - probably approaching a month's worth of my income up the time. ....

I still have the computer in question in a (very) dusty corner of my cellar. It's very large and, mainly thanks to its PSU, is almost too heavy to pick up easily! The below is one of the several RAM cards it contains. My recollections are obviously also pretty dusty but, since it contains 16 x 4116P chips (each 16K x 1 bit), I presume that the card as a whole must represent 4 KB of 8-bit memory ... in which case a mere 2,000,000 of those cards would presumably equate to the 8 GB of RAM I have in my current computer ...

Kind Regards, John

 

[Harry Bloomfield]

I still have the computer in question in a (very) dusty corner of my cellar. It's very large and, mainly thanks to its PSU, is almost too heavy to pick up easily! The below is one of the several RAM cards it contains. My recollections are obviously also pretty dusty but, since it contains 16 x 4116P chips (each 16K x 1 bit), I presume that the card as a whole must represent 4 KB of 8-bit memory ... in which case a mere 2,000,000 of those cards would presumably equate to the 8 GB of RAM I have in my current computer ...

My homebuilt used the same format of PCB and 64pin connector - Euroboard or something? Likewise 8Kb per PCB, but choice of static or EPROM. I ended wire wrapping an adaptor card for it, to S-100, to interface HDD's.

Those were exiting and adventurous days

 

[JohnW2]

My homebuilt used the same format of PCB and 64pin connector - Euroboard or something? Likewise 8Kb per PCB, but choice of static or EPROM. I ended wire wrapping an adaptor card for it, to S-100, to interface HDD's.

I started with static RAM, but that only worked out at 1 or 2 KB per (PCB) card, and was incredibly power hungry - so, as soon as I could afford to, I moved to dynamic chips. I must admit that if you'd asked me a few hours ago, I would have guessed/'remembered' that they were then 8 kB per board - but, as my arithmetic above indicates, it seems that it was only 4 KB.

Those were exiting and adventurous days

Indeed so

Kind Regards, John