[ros-dev] HDD Geometry switch

[chris]

RE: virtual disks, just place a note on the website and on the readme.txt found on the bootcd and tell people that they need to create a virtual machine that is 8 gigabytes or larger.its not rocket science.
  ----- Original Message ----- 
  From: Love Nystrom 
  To: ros-dev at reactos.org 
  Sent: Wednesday, November 30, 2011 2:25 PM
  Subject: Re: [ros-dev] HDD Geometry switch


  Olaf, please don't leave, the project needs you just
  as much as it needs the developers.

  Eric, Olaf's regression testing can not entail patching/rebuilding
  the system to accomodate disk structure (as you surely realize).
  That said, your reasons for change are sound, but perhaps you

  can make provisions to temporarily revert this if it causes massive
  problems. The timing _is_ not good if indeed a release is close
  at hand.. Can it wait until after the release?

  Alex, calling Olaf "not an OS tester" is a bit harsh, don't you think?
  Not everyone can be as weather hardened and experienced as you are.

  Regarding the reasons for change:

  Max CHS capacity: 10 bit C, 6 bit S, 8 bit H
  2^10 * 2^6 * 255 == 16711680 sect(512) == 8.5 GB

  This is the geometry Eric wants to use, which makes sense
  because it can utilize the full CHS addressing capacity,
  and reflects the absolute limit of BIOS int 13h CHS calls.

  Previous 32S 64H CHS limit:
  2^10 * 32 * 64 == 2097152 sect(512) == 1 GB



  This is an artificial and unnecessary limit, imposed by some
  strange design decision in Redmond a long long time ago.


  For non-devs: In CHS mode BIOS has an absolute disk limit of 8.5 GB,
  due to the available address bits, a 10/6 bit Cylinder/Sector composite,
  and an 8 bit head number. Any disk bigger than that can only be addressed
  in LBA mode (logical sector nr), which has a limit of 2^32 sectors == 2 TB.

  And, if anyone didn't know, the geometry parameters are stored
  in the boot sector, not in the MBR.
  There's more to it, but I stop at that.

  So.. Eric's change _should_ not cause any problem on disks
  larger than 8.5 GB, since they run in LBA mode by necessity.
  Concordingly, there could be forseeable problems on virtual disks
  which will often be smaller than 8 GB and may be running CHS mode.



  That'll be my penny to the pot for now.



  PS. A standard sector is 512 bytes. Bigger sectors, e.g 1kB, have been used
  in the past to increase capacity, but are _very_ unusual since they require
  proportionately higher bit frequencies on the media and are error-prone.



  Best Regards

  // Love




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