FDISK 'splain pelase?

I have been into computers since 1983 when I bought my first TRS80 and
I have a very high IQ. Yet, I cannot understand FDISK for the life of
me. I have always used Western Digital's, "LIFEGUARD", for new disks,
and FORMAT C: with Partition Magic for existing disks.

All I really need is a simple definition of: PRIMARY, SECONDARY,
LOGICAL and EXTENDED.
Thanks,
MIke
Mike

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Michael P Gabriel wrote:

> I have been into computers since 1983 when I bought my first TRS80 and
> I have a very high IQ. Yet, I cannot understand FDISK for the life of
> me. I have always used Western Digital's, "LIFEGUARD", for new disks,
> and FORMAT C: with Partition Magic for existing disks.
>
> All I really need is a simple definition of: PRIMARY, SECONDARY,
> LOGICAL and EXTENDED.
> Thanks,
> MIke
> Mike

Note: The following may be easier to read with a fixed-pitch typeface.

'FDISK', according to the IBM PC-DOS 7.0 manual, is short for 'Fixed Disk
Setup Program'.

The 'secondary partition' appears to apply to systems such as the IBM
i270, i820, i830, i840, and i890 systems, so I'll skip that

Hard drives can contain up to four 'primary' partitions per drive.
Under DOS-based operating environments only the 'active', or 'boot'
partition is accessible to the system.

Under 32-bit Windows systems (such as NT/2000 and probably XP), and as I
recall OS/2, a limited number of partition types are recognized. The
partition type is identified by a special code in the 'partition table'
which lives in the first sector (sector zero) of the hard disk.

Systems such as Linux can recognize a large number of partition types. If
support for the recognized types is available in the kernel or as a module,
the system can access the corresponding 'filesystem'.

The partition table also defines the type of filesystem that is expected
within each partition.
Under 32-bit Windows the options are for FAT-16, FAT-32, and NTFS. DOS-based
systems (MS-DOS, Win3.x through Win95 -prior to OSR2) were limited to
FAT-16 and FAT-12.

FAT-12 is still used on floppy diskettes but, as I recall, is no longer
supported under Windows for hard disks.

The size of a partition, and the choice of a filesystem (FAT, FAT-16, NTFS,
etc.) will also determine how much physical space is used to store files on
the hard disk.

// The table below was excerpted from the Microsoft Knowledge Base.

The following is a table of logical drive sizes, FAT (File Allocation Table)
types, and cluster sizes:
Drive Size FAT Type Sectors Cluster
(logical volume) Per Cluster Size
---------------- -------- ----------- -------
(Floppy Disks) 360K 12-bit 2 1K
720K 12-bit 2 1K
1.2 MB 12-bit 1 512 bytes
1.44 MB 12-bit 1 512 bytes
2.88 MB 12-bit 2 1K
(Hard Disks) 0 MB - 15 MB 12-bit 8 4K
16 MB - 127 MB 16-bit 4 2K
128 MB - 255 MB 16-bit 8 4K
256 MB - 511 MB 16-bit 16 8K
512 MB - 1023 MB 16-bit 32 16K
1024 MB - 2047 MB 16-bit 64 32K

// end excerpt

On drives up to 8 gigabytes, FAT-32 uses a cluster size of 4k (4,096 bytes).

Basically this shows that a larger cluster size wastes disk space:
If you have a 2 gig drive (2047 MB above) with its 32K cluster size, any
single file smaller than 32K will eat the entire 32K space.
A 33K file will eat 64K of disk space.

On an 8 gig drive under FAT-32 the same 33K file would only use 36K of disk
space.
NTFS on a 60 gig drive (under Windows 2000 SP3) uses a 4K cluster; on a 15
gig drive it shows a 512 byte cluster size.

I seem to recall that FAT-32 is 32K on large drives although I couldn't
verify that.

For all the DOS-based systems (including ME, as I recall), the system must
either be physically installed on the first primary partition or it must be
fooled into 'thinking' it's on the first primary partition.

Windows NT/2000, XP, OS/2, and Linux can generally be installed on, and
booted from, almost any partition.

An extended partition is useful if more than four partitions are desired on
a single drive.

In a DOS extended partition, you can typically have up to 23 'logical
drives'.
The extended partition essentially becomes a container wrapped around a
collection of smaller partitions.

I believe I got this all correct. Any extra comments are welcome.


Ron n1zhi

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On 31 Jan 2004 06:38:45 -0800, (Michael P Gabriel)
wrote:

>I have been into computers since 1983 when I bought my first TRS80 and
>I have a very high IQ. Yet, I cannot understand FDISK for the life of
>me. I have always used Western Digital's, "LIFEGUARD", for new disks,
>and FORMAT C: with Partition Magic for existing disks.
>
>All I really need is a simple definition of: PRIMARY, SECONDARY,
>LOGICAL and EXTENDED.
>Thanks,
>MIke
>Mike

Primary and Secondary usually refer to hard drive controller PC
architectural schemes, and the terms are inappropriate in an
elementary discussion of FDISK.

Primary, Extended, and Logical are the pertinent terms.

PC hard drives are encoded before use, with information describing to
the PC what portions of the hard drive are to be used for particular
purposes, or by particular operating systems. This encoding is often
created through use of FDISK.EXE.

The area on the hard disk designated to contain this encoding, called
the partition table, is very limited is size, and can describe only
four portions, or partitions, of the disk. These four partitions are
called Primary partitions.

To enable creation of more than four partitions, and also to meet the
requirements of some operating systems for non-primary partitions,
FDISK can give a special designation to a Primary partition. Usually
applied to the last established Primary, this designation as Extended
partition causes it to become a container for subordinate partitions,
usable for data storage, but such Extended partition is not, itself,
used for data storage. The usable, subordinate partitions created
within this container are called Logical partitions or 'drives'.

Since the Extended partition is allotted on the hard drive a space for
description of its Logical partitions, and that space is in form just
like the aforementioned partition table, an Extended partition is
limited to four subordinate Logical partitions. _However_ the last of
the four Logicals can be given the special Extended designation, so it
too can have four subordinate Logicals, and continuing, presumably
without limit.

http://www.ata-atapi.com is a good source for a pictorial
representation of this concept. If link is too old, search for Hale
Landis "How It Works".