[mythtv-users] 32 bit or 64bit???

Rod Smith mythtv at rodsbooks.com
Fri Jan 16 03:02:32 UTC 2009


On Thursday 15 January 2009 08:21:37 pm A JM wrote:
> If you were building a new backend/frontend would you go with a 32bit box
> or a 64bit box?

The hardware would definitely be 64-bit, and the software probably would be.

> Can you run a 32bit OS on a 64bit chip?

For anything in the x86-64 world (AMD Athlon 64, Intel Pentium 4 with EM64T, 
etc.), 32-bit OSes run fine. In fact, there aren't many 32-bit CPUs left in 
the Intel-compatible world. I haven't looked into it in any depth, but the 
main options from both AMD and Intel these days are 64-bit CPUs.

Outside of the x86/x86-64 world, there may be different rules, but presumably 
you're thinking of x86/x86-64 CPUs.

> Are there compiling differences in the ./configure between a 64bit and32bit
> OS and for that matter Myth?

I haven't delved into the MythTV configuration file in any detail; however, my 
recollection from configuring and compiling MythTV was that the configure 
script didn't offer me any options that would obviously affect 32- vs. 64-bit 
performance.

> Anyone have references to a guide for building a 64bit box as opposed to a
> 32bit box?

In terms of hardware, there are no important differences. If you've built 
32-bit x86 computers, the process for 64-bit x86-64 computers is the same. 
You'll encounter more differences because of new or changed technologies 
other than the CPU bus width, such as the shift from PATA to SATA for hard 
disk interfaces or the increasing popularity of physically smaller 
motherboards with integrated video.

Software installation is also identical on the two platforms, even down to the 
boot process -- x86-64 Linux distributions use GRUB or LILO, just like their 
x86 counterparts, and mainstream motherboard BIOSes are pretty similar, too. 
(Intel is pushing EFI as a replacement for the BIOS, but that shift hasn't 
yet gained much momentum for x86-64 systems outside of the Mac world.)

On most CPU platforms and for most tasks, the shift from 32-bit to 64-bit code 
provides no speed boost; however, x86-64 implements several architectural 
improvements, so that 64-bit code can actually be a bit faster than 32-bit 
code. I did some tests on this a few years ago, when the Athlon 64 was first 
released, and I found speed improvements of 10-30% on typical CPU-intensive 
tasks (gzipping files, encoding MP3s, etc.). I haven't attempted to benchmark 
MythTV or any related tasks with respect to 32- vs. 64-bit code, though, so I 
don't know how MythTV in particular will react. Note that a small number of 
programs show a decrease in performance when compiled in 64-bit form, 
typically because the code includes x86-specific optimizations (say, inline 
assembly code). I have a vague recollection of hearing that this was once 
true of some Linux multimedia tools, but that this is no longer true. 
Certainly my own transcoding operations (done with mythtranscode and 
mencoder) run at about the same speed on my 32- and 64-bit systems, which 
have CPUs of similar speed, so any differences in my own experience aren't 
dramatic.

As others have said, the availability of multimedia tools is another factor. 
MythTV runs fine in 64-bit mode, but if you rely on obscure -- and especially 
proprietary -- libraries, you should check on their availability in 64-bit 
mode. The last I checked, the 64-bit Adobe Flash library that's been 
mentioned by others is still in alpha test. I haven't tried it, so I don't 
know how good it is.

> My plan is to use Ubuntu with VDPAU and an Nvidia 8000 based board maybe
> the Zotac that was mentioned a little bit ago by Brad -
> http://www.newegg.com/Product/Product.aspx?Item=N82E16813500016 it seems
> like a strong enough board.

I notice that there are only two reviews of that board. Both give it only 3 of 
5 eggs and mention SPDIF audio output problems. Oh, and Newegg lists it as 
a "deactivated item," so you'd need to locate another supplier.

FWIW, I just put together a new non-Myth system based around the Biostar 
TA-780G (http://www.newegg.com/Product/Product.aspx?Item=N82E16813138105). It 
seems like a good board so far, but it's based on an ATI chipset, with Radeon 
HD 3200 graphics rather than nVidia, so if you really want VDPAU you'd need 
to add a PCIe card. I needed to install ATI's drivers to get the on-board 
video working under X. I liked the Biostar board because it's got four memory 
slots, so that I've got room for expansion even after starting with my 2x2GB 
configuration.

-- 
Rod Smith


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