114 lines
3.2 KiB
Plaintext
114 lines
3.2 KiB
Plaintext
.\" $NetBSD: prep,v 1.8 1999/05/04 20:07:02 fvdl Exp $
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First and foremost, before beginning the installation process,
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.Em make sure you have a reliable backup
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of any data on your hard disk that you
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wish to keep. Mistakes in partitioning your hard disk may lead
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to data loss.
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.Pp
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Before you begin, you should be aware of the geometry issues that may
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arise in relation to your hard disk. First of all, you should know
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about sector size. You can count on this to be 512 bytes; other sizes
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are rare (and currently not supported). Of particular interest are
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the number of sectors per track, the number of tracks per cylinder
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(also known as the number of heads), and the number of cylinders.
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Together they describe the disk geometry.
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.Pp
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The
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.Tn BIOS
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has a limit of 1024 cylinders and 63 sectors per track for
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doing
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.Tn BIOS
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I/O. This is because of the old programming interface
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to the
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.Tn BIOS
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that restricts these values. Most of the big disks
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currently being used have more than 1024 real cylinders. Some have
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more than 63 sectors per track. Therefore, the
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.Tn BIOS
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can be instructed
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to use a fake geometry that accesses most of the disk and the fake
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geometry has less than or equal to 1024 cylinders and less than or
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equal to 63 sectors. This is possible because the disks can be
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addressed in a way that is not restricted to these values, and the
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.Tn BIOS
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can internally perform a translation. This can be activated
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in most modern BIOSes by using
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.Em Large
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or
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.Em LBA
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mode for the disk.
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.Pp
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.Nx
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does not have the mentioned limitations with regard to the
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geometry. However, since the
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.Tn BIOS
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has to be used during startup,
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it is important to know about the geometry the
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.Tn BIOS
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uses. The
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.Nx
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kernel should be on a part of the disk where it can be loaded using the
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.Tn BIOS ,
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within the limitations of the
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.Tn BIOS
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geometry. The install program will check this for you, and
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will give you a chance to correct this if this is not the case.
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.Pp
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If you have not yet installed any other systems on the hard disk
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that you plan to install
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.Nx
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on, or if you plan to use the
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disk entirely for
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.Nx ,
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you may wish to check your
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.Tn BIOS
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settings for the 'Large' or 'LBA' modes, and activate
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them for the hard disk in question. While they are not needed
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by
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.Nx
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as such, doing so will remove the limitations mentioned
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above, and will avoid hassle should you wish to share the disk with
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other systems. Do
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.Em not
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change these settings if you already have
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data on the disk that you want to preserve!
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.Pp
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In any case, it is wise to check your the
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.Tn BIOS
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settings for the
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hard disk geometry before beginning the installation, and write
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them down. While this should usually not be needed, it enables
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you to verify that the install program determines these values
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correctly.
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.Pp
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The geometry that the
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.Tn BIOS
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uses will be referred to as the
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.Tn Em BIOS
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.Em geometry ,
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the geometry that
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.Nx
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uses is the
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.Em real geometry .
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.Pp
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.Li Sysinst
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will try to discover both the real geometry and
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.Tn BIOS
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geometry.
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.Pp
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It is
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.Em important
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that
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.Li sysinst
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know the proper
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.Tn BIOS
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geometry to be able
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to get
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.Nx
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to boot, regardless of where on your disk you put it.
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It is less of a concern if the disk is going to be used entirely for
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.Nx .
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If you intend to have several OSes on your disk, this becomes
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a much larger issue.
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