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[ The PC Guide | Systems and Components Reference Guide | Motherboard and System Devices | System BIOS | BIOS Settings | IDE Device Setup / Autodetection ]

Translation Mode

This setting specifies the translation and/or addressing mode for the drive. These special modes are used to enable the BIOS (and operating system) to handle large hard drives and overcome hard disk capacity barriers, especially the infamous 504 binary megabyte / 528 decimal megabyte barrier.

The exact options for this setting will vary by system. These are the ones you are most likely to see:

  • Normal or CHS: This mode is sometimes called "CHS" mode, for "cylinder, head, sector", the three geometry specifications for a hard disk. This is the "standard" mode with no special translation or addressing. It is used for regular IDE/ATA hard disks that are smaller than 504 MB; more precisely, it should be used for any hard disk that has 1,024 or fewer cylinders and 16 or fewer heads.
  • LBA: This stands for "logical block addressing". Instead of referring to locations by passing to the disk a cylinder, head and sector number (CHS addressing), the sectors are serialized so that each just has an integer number; 0, 1, 2, etc. up to the total number of sectors on the disk. LBA is now pretty much the standard for addressing large hard disks, and is recommended for hard disks that are not small enough to be used under "Normal" mode. When LBA mode is used, the autodetect program will still translate the drive parameters so that the number of cylinders is less than 1,024, the BIOS limit. However, accesses to the disk will be based on the integer sector number.
  • Large: This mode is also sometimes called "ECHS" mode, standing for "Extended CHS". This mode uses translation to ensure that the number of cylinders is less than 1,024. However, unlike LBA, it does not then number the sectors linearly, it refers to the disk using the translated cylinder, head and sector values. This is a valid way to deal with larger hard disks, however it is very rarely used and is now considered non-standard. Using this mode is therefore not generally recommended.
  • Auto: Some BIOSes will automatically detect and set the hard disk mode at boot time. Some BIOSes have the ability to dynamically autodetect all drive settings at boot time. However, even if you aren't using this overall boot-time autodetection, you can use this specific mode autodetection if your BIOS supports it, in most cases.

The BIOS autodetection program will normally take care of making the appropriate mode selection for you (either if you use the "Auto" setting or if you autodetect the drive); in some BIOSes it will only "recommend" the correct mode, but this recommendation is usually accurate. Yet another reason to use autodetection. :^)

Warning: There are a lot of caveats and special rules about how drive translation and addressing works. This is all discussed in more detail in this section.

Warning: Changing the mode on your hard disk, for example from Large to LBA or vice-versa, can change the translation method that your BIOS uses for the drive. This can also happen if you move a drive from a computer that doesn't use LBA to one that does use it. If the translation mode changes you run the risk of losing all the data on the drive. It is recommended that you not change translation methods unless there is a specific reason to do so, and that you back up your data before changing these types of settings in the BIOS.

Next: Block Mode

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