CurtPalme.com Home Theater Forum

oliverg · Posted: Mon Jul 02, 2007 11:58 pm Post subject:

Sorry Mark, but a 1080p bitstream requires more bandwidth than a 1080i bitstream. File size is irrelevant, its the amount of bandwidth the bitstream demands that is important.

racerxnet · Joined: 20 Jun 2007 Posts: 362 Location: Illinois

oliverg · Posted: Tue Jul 03, 2007 4:31 am Post subject:

I'm talking 1080p/H264 etc - the processing and disk access requirements are much greater than earlier adoptions of HD.

Firewire/USB (especially on the PC under Windows) has to be polled via interupts - devices like ATA and SATA have the advantage of DMA.

What you are quioting above are peak transfer rates. In real world applications, you wont be able to sustain these.

I have actually tried to do this and it failed - I then realised the content was on a Firewire drive - copied it to a 10k spin SATA2 drive and the choppiness went away instantly.

Ever tried installing Windows to a FW/USB2 drive? It doesn't work. Swap file access is way too slow as the INT polling chews up CPU cycles dramatically.

Anyway, believe what you will - when/if you try to deliver 1080p using a FW/USB2 device you will encounter a lot of problems.

Dont you think that motherboard manufacturers would start using USB/FW drives instead of SATA/SATA2/PATA if they thought they could get away with it?

USB/FW was never intended as a primary data access/storage mechanism - secondary at best.

Axatax · Posted: Tue Jul 03, 2007 4:49 am Post subject:

oliverg · Posted: Tue Jul 03, 2007 4:58 am Post subject:

Quoted from a tuning site and probably explains better than I,

"Windows & Firewire Communication
All communicatiions (e.g. reading and writing via your firewire card) and handled using interrupts. . Each device (e.g. firewire card, printer etc) which uses an interrupt has a priority"

"Things get even worse if we examine how Windows services the interrupts using polling. What this means is that when an interrupt is serviced the computer (instead of carrying down the priority list) goes back to the top of the priority list to ensure that another card/service with a higher priority than your firewire card needs attention. If your firewire card was installed late it has a low priority, and as a result gets little attention. Unfortunately, your firewire card is usually one of the last to be installed, so its priority is way down the list - and doesn't get sufficient attention to properly handle the transfer of video, thus you start getting problems.

The priority of devices are set in stone (actually they are buried in your registry) "

This is a pretty accurate depiction.

Go on, install Windows onto a USB/FW drive and see how it runs - try delivering 1080p reliably - its not just about throughput - there is a lot happening behind the scenes - hardware video acceleration, drive access in the future decryption of HDCP etc.

To deliver 1080p reliably, you can't rely on anything other than a primary storage medium - eg a dedicated raid card, sata, sata2, pata etc.

You dont want stuttering and choppy play when you are sitting back watching a movie.

Axatax · Posted: Tue Jul 03, 2007 5:09 am Post subject:

Sorry, that description is not correct. For a driver to determine a hardware state change, a driver will employ an interrupt handler, will read data from a specific IO port, or will read from a memory region (or a selector in the case of Windows). These two strategies are mutually exclusive. An interrupt cannot be polled. Its function is to halt the CPU, then jump to a ISR (or Interrupt Service Routine) installed by driver. Interrupts are a fundamenal principal in computing, are well understood, and are undisputed.

oliverg · Posted: Tue Jul 03, 2007 5:56 am Post subject:

What I'm trying to say - for example, when you have com port activity, the processor polls int 14 - and in doing this, it will lock the PC up. That's one of the reasons serial interfaces became redundant, when a modem was pulling down data, the PC would be locking

I understand that what you are referring to in regards to polling and interrupts being mutually exclusive. I think its a question of your intepretation - regardless of symantecs, my point is that USB/FW devices are handled differently to SATA/PATA devices, I'm not here to get into a debate on the mechanics of how USB /FW devices are accessed differently to SATA/PATA/dedicated RAID cards - suffice to say that they are.

I've actually gone through this process - it is easy to replicate. I daresay no-one above has actually tried to use their HTPC to stream 1080p from a USB device. If you do some googling, you will see that I'm not the only one who has encountered this problem. I'll try to dig some links up.

Axatax · Posted: Tue Jul 03, 2007 6:32 am Post subject:

oliverg · Posted: Tue Jul 03, 2007 8:01 am Post subject:

This is all well and good Axatax but as I said, I'm not here to debate the mechanics - needless to say, USB/Firewire devices are not designed to be primary access/storage mediums - you keep trying to debate symantecs with me and are missing the point entirely

Axatax · Posted: Tue Jul 03, 2007 8:12 am Post subject:

oliverg · Posted: Tue Jul 03, 2007 8:32 am Post subject:

Allow me to clarify. I am referring to primary storage methods as per online/ nearline storage - USB/FW2 are tantamount to nearline - and not designed as a primary storage/access device. We are not discussing RAM at this point. You definitions are your own as are your opinions.

Stop hijacking the thread with your attempt symantecs and try contributing to the discussion in a more positive way - instead of being a pedant? When I started this thread, it was about appliances and HTPCs, lets continue along those lines rather than going completely off topic

Axatax · Posted: Tue Jul 03, 2007 8:39 am Post subject:

oliverg · Posted: Tue Jul 03, 2007 8:41 am Post subject:

Obviously you understand what I'm talking about but you just want to act like a wanker

http://en.wikipedia.org/wiki/Wanker

Cursory understanding? I've been in IT since 1981, ex Apple and Microsoft Australia - i OWN an IT company which is a Certified Microsft Partner, I'm personally a Microsoft Certified Systems Engineer (1996) and a current Fellow of the Australian Computer Society. I have a Masters in Business Information Technology (1992)- If you want to act like a pedant, please do so in another thread, not mine.

Axatax · Posted: Tue Jul 03, 2007 9:12 am Post subject:

oliverg · Posted: Tue Jul 03, 2007 9:17 am Post subject:

No I'm not a programmer but I used to have limited experience in 6502 assembly langauge.. come on Axatax, you know what I'm talking about - why act the way you have? Instead of disagreeing with the actual points I made, you chose to debate symantecs. If you are as experienced as you make out, you know what I'm saying is true.

Axatax · Posted: Tue Jul 03, 2007 9:31 am Post subject:

oliverg · Posted: Tue Jul 03, 2007 9:59 am Post subject:

We agree then. I haven't stated that it wouldn't work in my earlier posts - I did say it would cause problems and that it isn't ideal. Peak transfer rates can't always be maintained with USB/FW. Anyway, thanks for your input Axatax.

Kind regards

PS do you know how different the XBox's architecture is to the PC? Is it able to 'protect' the integrity of a HD bitsteam, or does it just use an inordinate amount of buffering?

Axatax · Posted: Tue Jul 03, 2007 10:17 am Post subject:

Phil Smith · Joined: 08 Mar 2006 Posts: 7717

You guys are WAY over my head. Shocked

Last night I transfered a 6.35Gb folder from my firewire drive case to my HTPC's hard drive, to get an idea of what the speed and CPU load is. It took about 3 1/2 minutes to transfer. CPU usage bounced around from 2% to 9%, and probably averaged 5%.

I believe that's an average of about 30Mbps. I'm not sure how much band width 1080p requires, but it's several times less than that, right? At the lower bandwidth of 1080p, I would assume my CPU usage would also significantly reduce. CPU usage is already not that much, so you would think would become insignificant when transferring 1080p.

I'm not sure the true meaning of my results, but it seems to me my rig can handle 1080p without even breaking a sweat.

PS: oliverg, you get angry when people don't agree with you. I don't see any point in that, especially in this discussion. You're getting pissed at Axatax for disagreeing with you, when it appears to me he's more knowledgeable. Just like with your and my HTPCs, you're turning into a pissing match.

oliverg · Posted: Wed Jul 04, 2007 10:05 pm Post subject:

Hi Phil, I get angry when someone is seemingly acting like a troll instead of discussing the ACTUAL issues we were discussing. In the end, Axatax wanted to debate about definitions of words when he knew exactly what I was talking about. In the end, he even agreed with me. He knew what I was saying was true, but it seemed to me he was trying to discuss things issues which weren't relevant. The fact that my interpretation of the finer details of interupts/polling are different to his didn't mean that my main points (which in the end he confirmed) were invalid.

When I was referring to "A" primary storage medium not "THE" primary storage medium - we were talking about USB/FW vs SATA/PATA etc not the whole PC architecture. He knew what I was talking about exactly but for because I had quoted some text from a 3rd party site, he thought I didn't know what I was talking about and took it upon himself to crusade and nit pick. I dont mind this but focus on the central issues of the thread, not go off on tangents that have no bearing on the main points.

How int/polling works is irrelevant - the main point is that USB/FW drives are accessed differently and in a way which isn't ideal. Hell, Aratax even went so far as to USB drives arent ideal for SD delivery and he's spot on.

I didn't understand why he wouldn't agree with me in the first place when he did in the end. I'm not a low level programmer which Axatax has more experience with, I'm a networks egineer. I might not be able to go into interupt/polling theory in as much depth, but once again - this wasn't the issue at hand. Knowing that two things are different is enough to maintain a point without knowing exactly how they are different. He wasn't debating the fact that they were different, he was having a go out how I expressed myself. IMHO he should have said 'look, what you are saying is right, but interupts work like this...'. and explained. But he was intent on trying to discredit me, not contribute in a positive way to the discussion.

Others keep saying 'but the bandwidth is there' and quoting bandwidth figures - on paper, it is - but those devices aren't able to sustain peak bandwidth and when trying to maintain a bitstream uniniterupted, they have issues. SATA/PATA/RAID does not suffer from those issues.

You would find you could watch 5-10-20 minutes of 1080p video with no problems and for 'no reason' your video would start stuttering - this wouldn't happen with S/P/R. Would people accept this from an appliance? No way!

As for 'your and my HTPCs', you said that I hadn't experienced what a good HTPC was - how could you possibly say that when your PC isn't as good as mine? I wasn't trying to get into pissing competition, but you can't say I 'hadn't experienced a good HTPC' when yours wasn't in the same ballpark and you were making out how good yours was. You took it as a pissing competion - all I was trying to do was point out to you that you can't make statements like that when your equipment itself is sub-standard to mine.

Anyway, if you want to believe that your PC can do 1080p with no issues, go ahead. I'll stick to my appliances and continue to keep my HTPC in its excellent context.