[mythtv-users] Starting Up

Michael T. Dean mtdean at thirdcontact.com
Sat Jan 14 03:36:21 UTC 2006

MR M T Golledge wrote:

>However, I'm concerned with the specifications of the PC and would like your 
>thoughts before I get going (I expect further down the line I'll get a 
>separate server as at the moment I've only got a couple of 40Gb hard drives 
>in the PC therefore a total of 80Gb - I don't think my motherboard will be 
>able to cope with anything higher than 40GB looking at the Intel website):
What, do you think we're talking about Windows?  ;)

The motherboard's BIOS may have a limit on the size of HDD it can
access.  Therefore, any kernel that uses the BIOS for accessing the HDD
(like the DOS/Windows kernels) can only access data that falls within
the first <limit>GB of the HDD.  Fortunately, BIOS and chipset
manufacturers did Linux users a great big favor by creating BIOS's with
varying and severe bugs.  Therefore, when creating the code to access
HDD's in Linux, developers had to choose between writing code to deal
with all the bugs in the BIOS's (i.e. like the Via 4-in-1 drivers, or
the Intel Bus Master drivers, or any of the other IDE drivers you have
to install in Windows) or to completely circumvent the BIOS.  The second
solution--although it required a bit more up-front development work--was
determined to be significantly easier in the long term (for Windows, the
first solution was easier because Microsoft left development of the
drivers up to the BIOS/chipset vendors).  Therefore, Linux does /not/
use the BIOS to access the HDD.

However, you still need to allow the BIOS to access enough of the HDD to
execute the boot loader and possibly for the boot loader to find the
kernel.  On Linux, you have two options.  First, you can create a small
partition at the beginning of the disk that contains your "/boot"
directory (i.e. a boot partition).  If doing this, you can often let the
BIOS autodetect the drive (which it may say is a 33.8GB HDD even though
it's much larger), and once you're in Linux, you'll have access to the
entire drive.

Some BIOS's, however, will refuse to autodetect the HDD if it's greater
than the maximum supported size.  If so, you just manually specify the
HDD parameters in the BIOS (i.e. 16383 cylinders, 16 heads, and 63
sectors--making the BIOS see the HDD as an 8.4GB drive) and make sure
your boot partition (or at least the /boot directory) is within the
first 8.4GB of the HDD (I generally make an 8-, 16-, or 24-MB
partition--depending on the function of the system--at the beginning of
the HDD for /boot).  Note that when specifying a disk geometry, having a
separate boot partition may not be required, but generally makes things
much easier.

If the disk isn't your boot disk, things are much easier.  Just tell the
BIOS that the disk doesn't exist (i.e. put "None" in for IDE 0 slave or

I used to have a Pentium 100/MMX that had a 2.1GB BIOS limit (and
wouldn't detect drives larger than that size) and I ran it with a 200GB
HDD without problems (until lightning took out the motherboard--stupid
cable modem).  Now, I have an AMD K6-2/380 with an 8.4GB limit using an
80GB HDD for a boot disk.  The one problem, though, is that although you
buy an ATA 6 (UDMA/100) HDD, you'll be using a much slower access
mode--which seems a waste.  Your motherboard is likely to only support
UDMA/33 or UDMA/66 (my Pentium 100 used PIO Mode 4, my K6-2 uses
UDMA/33).  UDMA/66 probably isn't a problem, but UDMA/33 may be
depending on number of tuners, settings for commflagging and
transcoding, etc.

Many HDD's also have a jumper that allows you to set them to appear as
small disks.  I've never used this approach.  Some of these just make
the disk report its geometry to the BIOS differently, but others
completely disable access to the rest of the disk at the HDD level (so
even Linux can't work around it).  Generally, Linux users shouldn't use
the jumpers on disks to change perceived disk size.

Oh, and make sure you don't have a disk manager on the disk (i.e. never
stick one of those floppies that comes with the hard drive in the floppy

See http://tldp.org/HOWTO/Large-Disk-HOWTO.html for details.

That being said, though, IMHO, getting a "dirt-cheap" new computer may
be worthwhile to allow for better commflagging.  I highly recommend
something in the 2GHz (or, in AMD parlance, 2000+ ;) range.  All you
need for a dedicated Myth backend is a case/power supply, motherboard
with integrated audio/video/LAN, CPU, memory, and hard drives (no need
for floppies or CD/DVD).  If you forego the integrated video, you can
get a GeForce 4 MX440 and make it a combined backend/frontend (and add a
DVD if you want to use MythDVD).  Don't know about UK prices, but I've
purchased about 20 systems (one by one) like this over the last couple
of years for about $150 each in the US.

However, I may not be well-qualified to make this recommendation as I
just upgraded my AMD Athlon XP 2000+ combined frontend/backend to a
dedicated AMD Athlon X2 4800+ frontend and an Athlon XP 2400+ backend
for a high-def setup, so, obviously, I feel my Myth box is worth
spending some money on.


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