[CALUG] Fedora upgrade .... CALUG Digest, Vol 54, Issue 14

[Bryan J Smith]

For backward compatibility, max sectors is 63, heads is 255, in CHS.  So 32/128 
would be 4MiB, not 8MiB, cylinders (and MiB, not GiB).  The maximum 63/255 is 
just under 8MiB, not a perfect boundary.  Many people are using 32/64 for 1MiB, 
although beware of translations that show up.

PC BIOS 16-bit Extended Int13h define most of the legacy structures.  For the 
most part, I just note that things are stored in the first 1MiB (first 2048x512b 
or 256x4KiB sectors) which is considered the MBR.  This has been respected for 
several years now by NT5.1 (XP/2003) and NT6.x (Vista, 7, 2008), so I usually 
just stick with it.

None of this matters with 64-bit uEFI and GPT, of course.

-- Bryan

FYI, Virtually all fixed disks models today are coming with 4KiB sector size.  
Many come with a jumper for 512b emulation that is on by default, but they are 
4KiB.  Until I see universal tool support for 4KiB, I leave the jumper on.  
After all, most everything else is aligned on 4KiB or 8KiB structures anyway, 
and shouldn't be accessing individual 512b bytes.




----- Original Message ----
From: James Ewing Cottrell 3rd <JECottrell3 at comcast.net>
Sent: Tue, June 21, 2011 7:41:38 PM

  I like the exact boundary argument. I was also considering 128 and 
128, giving exactly 8G cylinders.

But I am wondering...where is the geometry stored? The old DOS used to 
have a BPB..."BIOS Parameter Block" that stored the geometry. But I made 
some new partition tables with odd sizes and didn't see the sizes I gave 
anywhere.

The other question I have is: What is the maximum size I can read at 
once with out the driver splitting it up into two different reads?

JIM

P.S. Who uses 4K blocks? I know that some companies (Pyramid was one) 
often used 2K Physical Sectors. I don't doubt you...I am just wondering 
who/where they are.