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Introduction
to Format Command
First of all, (you don't have to FDISK/Partition your H-D first,
because you might just want to Restore (Clean-Up) Windows or just
want a extra storage area, so just FORMAT/Re-FORMAT it and it's
done.
Formatting is the process of writing marks on the Hard Drive or
(removable) Magnetic media that are used to mark tracks and sectors.
Before a disk is formatted, its magnetic surface is a complete mess
of magnetic signals. When it is formatted, some order is brought
into the chaos by essentially drawing lines where the tracks go,
and where they are divided into sectors.
The actual details are not quite exactly like this, but that is
irrelevant. What is important is that a disk cannot be used unless
it has been formatted. The terminology is a bit confusing here:
in MS-DOS, the word formatting is used to cover also the process
of creating a file system. There, the two processes are often combined,
especially for floppies. Where the distinction needs to be made,
the real world Unix techies call formatting (low-level formatting,
while making the file system is called high-level formatting) and
we combine the two and call it formatting.
Ok, you've learned that your platter (disk) is a mass storage device
generally made of metal, covered with a thin layer of iron oxide
of which has good magnetic properties. Computers record data in
bits, 8 bits to a byte and 512 bytes to a sector. The Windows OS
knows where all your stuff is at upon request. Even the smallest
hard drive can store millions of bits and must be organized---called
(formatting).
First, a hard drive has to be physically formatted before it can
be logically formatted. This (low-level) formatting is done by the
drive manufacturer (IDE) and divides the platter into tracks, sectors
and cylinders----these are called physical elements. Tracks are
circular paths around your disk and are identified by a number starting
with (0) at the outer edge. The set of tracks that lie at the same
distance from the center on all sides of all platters are called
a cylinder. Tracks are divided into areas called sectors.
Sectors are usually formatted to contain 4096 bits or 512 bytes.
After this physical format--it's ready for logical formatting.
Logical formatting places a file system on your disk and a file
system allows an operating system like (Windows-95) to use this
space to store and retrieve files. So, this is what you do is a
logical formatting using it's operating utility.
This means you can format a Hard-Drive and use it right away for
a storage container just like you've been doing on the floppies
since you know when, then use it as a back-up data area or what
ever. A disk can be divided into partitions and then formatting
is applied.
After you partition and format---it's called a (volume). This is
why you should give it a name or (label) so you can identify it.
So, you now (hopefully) understand why you have to format.
Format
Switches
FORMAT = places a file system on the disk for storage or a operating
system.
FORMAT /c - Causes FORMAT to retest bad clusters, otherwise FORMAT
will mark the clusters as bad but will not retest them.
FORMAT /s = prepares a partition or disk to make it active or bootable.
FORMAT /mbr = creates a new boot sector and should only be used
as a last resort.
FORMAT /q =this is mostly unknown but seems to work if your having
problems getting the W95 setup to work (not recommended unless it's
a last ditch effort).
FORMAT /U = Does a unconditional format, so do the SYS C: to get
system files -- then a through scandisk to fix any errors. This
FORMAT /U parameter performs an UNCONDITIONAL format, which DESTROYS
every byte of data on a disk by overwriting it with.
WARNING: You CANNOT UNFORMAT a disk
formatted using the /U option!
FORMAT /SELECT /U This particular
combination of FORMAT.COM parameters makes a disk UNREADABLE! WARNING:
DO NOT use these two FORMAT switches TOGETHER on ANY drive!
FORMAT /Z:n formats a FAT32 drive with a cluster size of n times
512 bytes. Meaning: drive: = your hard drive letter (C:, D:, etc).
n = number of sectors per cluster multiplied by 512 = cluster size
in bytes. Examples: n = 1 creates a 512 bytes cluster; n = 2 creates
a 1024 bytes (1 KB) cluster; n = ? creates a ? x 512 = ???? bytes
(???? bytes : 1024 = ? KB) cluster.
NOTE: Almost all manufactures of hard drives (these days) come
formatted and most will come with a program disk for formatting,
partitioning and moving your system from your old hard drive to
the new one.
Low-Level
Formatting Explained:
Cylinder: concentrical tracks on one or more disksides
the harddrive's read/write head can be positioned over. The heads
are mounted on a "fork" which positions all heads in a
certain cylinder position.
Head Side: this refers to the harddrive's read/write
head currently active. Since most harddrive's have at least 2 heads
also the term Side is used for referring which disk and side has
an "active" head over it.
Track: the combination of the cylinder all heads
are over, and the selected head.
Sector: the smallest unit that can be read from/written
to a disk. Without special drivers, DOS and windows can only cope
with 512-byte sectors.
BootSector: (ie:, the first sector in each partition).
It stores information like the number of sectors/cluster, the partitionsize,
the number of sectors/FAT and the number of sectors in the partition.
Also it has code to load IO.SYS and MSDOS.SYS which are used by
the boot process which is of course only used in the active, primary
partition that is used to boot.
Formatting & Low-Level Formatting
This is very confusing to most people. Formatting a floppy generally
means that BOTH a low-level and a high-level format take place.
The low-level format overwrites full tracks consisting of multiple
sectors, headers and trailers.Each sector is preceded by a header
and gets a trailer written behind it. Only the sectors and trailers
are updated when you copy a file to the floppy (effectively writing
sectors), the headers are used for finding the start of each sector
on the track and are only read from (except during a format operation).
The low-level format calculates a CRC-checksum (CRC = Cyclic Redundancy
Check, a special algorithm that is very sensitive to even the slightest
change in data) from each sector it writes, and writes that calculated
checksum to the trailer.
After low-level-formatting each track, the format program simply
reads all sectors and trailers in it, recalculates the checksum
from each sector and compares it to the checksum in the trailer.
If they don't match, the sector is considered "bad". It
stores all bad sector locations in RAM for later use.
After finishing ALL tracks on both sides, the format program will
do a high-level format of the floppy. That means that it will write
a proper bootsector, clear both FAT's and the rootdirectory of the
drive.
Then it will recall the bad sectors found and adjust the FAT's accordingly.
What is Low/High Level Formatting ?
A low-level format (first done at the factory) draws magnetic lines
on the hard disk, these days you rarely need to redo a low-level
format.
A high-level format creates a new FAT and scans the surface of
the disk, finding and marking damaged sectors (those corrupted files).
Performing a high-level format is deceptively easy; simply run the
Format utility.
However, the DOS FORMAT program only knows how to low-level format
floppies, not harddrive's, due to the fact that sector header/trailer
information varies widely between harddrive manufacturers and models.
Further, the number of sectors on a track is fixed for floppies
in (DOS floppy formats) but varies on most harddrive's.
Finally, EIDE harddrive's are preformatted by the manufacturer
typically with dedicated programs that leave some space on the drive
to "remap" bad sectors to, should they show up over time.
This means that if the microcontroller in the drive detects a bad
sector, it will try to reread a number of times until the checksum
matches. Then it will mark that sector as bad, and store the information
in another sector. All this is invisible from DOS. However, for
fast AV or multi-speed CDROM writers this may mean a hickup in the
datastream coming from the drive, not only when the bad sector is
detected, but also afterwards because the drive will have to get
the sector data from another physical location on the drive involving
extra head-seeks.
Therefore, instead of low-level formatting your EIDE drive when
it was trashed, first make sure that there are no other problems
involved (i.e. too fast PIO mode, wd-ctrl in use for a large incompatible
drives, buggy CDROM drivers, too long (ribbons) between your controller
and drives, bad RAM or bad cache RAM etc).
I strongly advise you NOT to use
the "format" option inside most BIOS's (reachable from
the BIOS setup screen). This FORMAT option was useful for old MFM
and RLL drives, and usually DESTROYS EIDE drives!
If you need to "repair"
an EIDE drive (bad sectors, or "indestructible" viruses
etc.) it is best to use a tool that simply overwrites all sectors.
This will force the drive to "remap" bad sectors itself.
Nearly all bad sectors that are not remapped can be detected by
either FORMAT or SCANDISK (surface scan option) and they will mark
the clusters containing bad sectors as bad in the FAT.
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