| General
information |
| Terminology: |
Description: |
| Sector |
Data
is stored on a disk by arranging it in bytes, simply put. It is however
not possible to read an individual byte from the disk; you have to read
512 at a time. 1 sector contains 512 bytes, so a sector is the smallest
addressable area on a disk. |
| Cluster |
An operating system
doesn't access the disk per sector, it accesses the disk per cluster. A
cluster is a number of sectors that are read or written as a group. So,
a
partition is divided into clusters, which in turn are made up of
sectors, which in turn are made up of bytes. |
| Partition/Volume |
A region of a disk
that is used for file storage. An empty disk by itself can not be used
to store data: partitions (or volumes) must be created on the disk so
the operating system knows where to put the files. A disk can be divided
into many partitions. Usually 1 disk contains 1 partition which takes up
all the disk's space, but since the introduction of Windows 2000 there
is actually no real limit to how many partitions can be on a disk. In
fact, it's often considered good practice to create 1 partition for the
operating system and 1 or more partitions for data storage. Partitions
need to be formatted before they can be used (as explained under
"partition types: formatted as..."). |
| Basic/Dynamic
disks |
A description of disk types that is
used in Windows (2000 and up): a Basic disk contains simple volumes
(using the "old fashioned" partition table to describe partitions), a
Dynamic disk allows for more types of volumes such as spanned/mirrored/raid/striped.
Read more in the Microsoft knowledge base (link).
Added confusion: the elements of a dynamic disk are usually referred to
as "volumes", while the partitions that are on a basic disk
are usually referred to as "partitions". We can only speculate
as to why this is but it may have something to do with the fact that
partitions have their own partition table entries in the MBR and dynamic
disk volumes do not. After all, it's called a partition table. Although,
it's also been named volume table (but not that often). Confused yet?
Essentially though, volumes and partitions are the same thing. |
| Disk
facts |
A hard
disk (the physical device) is made up of platters. To be able to find a
specific location on the disk it is divided into cylinders, each
cylinder is divided into tracks (or heads) and each track is divided
into sectors. In earlier days these numbers were vital. Nowadays we use
LBA addressing and the cylinder/head/sector numbers are no longer used
to identify a disk location, but they still play a part when partitions
are created. It is important that the PC recognizes the disk correctly
(size, head and sector values must correspond to what the manufacturer
states). |
| LBA
address
|
LBA
stands for Logical Block Addressing. This is simply a way to identify
each sector on a disk: the first sector on a disk (the MBR) is numbered
0 and all following sectors are numbered sequentially. So a LBA address
is nothing more than a sector number. Keep in mind that the count starts
at 0; LBA sector 10 is the 11th sector on the disk. |
| Disk
geometry |
Geometry consists of 2 values: heads (per cylinder) and
sectors (per track). These values can differ from disk to disk, but are
generally 255 (heads) and 63 (sectors). Although modern operating systems
don't need to do this anymore, these values are still used when
creating (basic) disk partitions. As such it is important that the PC has
the correct values for the disk; if the values are wrong the operating
system will not be able to find certain important structures on the disk
and fail to boot, or even fail to access the partition completely.
|
| S.M.A.R.T. |
Self Monitoring,
Analysis and Reporting Technology.
This is a monitoring system for computer hard disks to detect and report
on various indicators of reliability, in the hope of anticipating
failures. All modern day hard disks have SMART technology on board.
SMART keeps an eye on various aspects of the hard disk (spin up counts,
bad sector count, number of hours used etc.) and attempts to predict
problems by analyzing the data that is gathered and comparing that against
certain threshold values.
For instance, say the disk has developed a number of bad sectors. Usually
that doesn't have to be a problem since these sectors are taken out of
commission and are replaced by sectors from a spare pool. But this can not
go on indefinitely; at some point either the spare sectors run out or the
amount of bad sectors is growing so rapidly that the disk will cease to
function within the near future. SMART would keep an eye on these
emerging bad sectors and once the amount of bad sectors has crossed a
threshold value, SMART takes note.
Understand that SMART itself will not notify the user; a SMART capable
utility or operating system is needed to receive these warnings. For
instance, the SMART tool that is included in the DiskPatch distribution
can check the status of your disk by reading and interpreting the SMART status.
|
| Partition
Table repair with DiskPatch |
| Terminology: |
Description: |
| MBR |
The Master Boot Record, the first
sector on the disk. Contains the partition tables (a list that describes
the locations of partitions on the disk). |
| EPBR |
Like
the MBR, this sector contains a partition table. But unlike the MBR, the
EPBR can be anywhere on the disk. An EPBR describes a logical partition
and can be found on disk just before the position where the logical
partition starts. |
| Partition
Tables |
These
describe the various partitions on the disk: where they start, how big
they are, what type they are. The MBR contains a partition table.
A partition table has space for 4 entries, meaning that 4 partitions of
any type is the maximum that can be created. This can be circumvented by
creating at least 1 extended partition, which in turn can contain many
more logical partitions. A common setup is 1 or 2 primary partitions and
1 extended that contains the rest of the partitions. Primary partitions
are the only ones that can be used to start an operating system from.
If Dynamic disks are used the partition table explanation as described
here does not apply anymore. |
Partition
types:
primary/extended/logical |
Primary
partitions are the only types that allow you to boot an operating
system. In general, you would install the operating system in a primary
partition. A primary partition can be set "active", which allows the
computer to locate the operating system that needs to be started. Only 1
primary partition can be active, but more primary partitions can exist.
If more than 1 primary partition is set active, the computer will not
boot. Also, when no primary partition is set active, the computer will
not boot. Only the partition table in the MBR can contain primary
partitions.
Extended partitions are nothing more than "containers" for
logical partitions. In general, all space that is not used by primary
partitions must first be added to an extended partition before logical
partitions can be created. Only 1 extended partition can exist per disk.
The partition table entry that describes the extended partition is in
the MBR.
Logical partitions are the partitions that are created in the
extended partition area. More than 1 logical partition can exist in the
extended partition area.
Note that when using Dynamic disks these rules don't apply anymore.
More information can be found in this knowledgebase article (link). |
Partition
types:
formatted as FAT/NTFS/etc. |
A
partition needs to be formatted before it can be used. Different
operating systems offer/require different format types:
DOS and older Windows versions (9x/ME) use a FAT type format. Newer
Windows versions (NT/2000/2003/XP/Vista) can also use NTFS type formats
(NTFS is preferred, it is more reliable than FAT). Other operating
systems use different formats: Linux uses EXT2/EXT3, OS/2 uses HPFS,
etc.
NTFS stands for New Technology File System. |
Partition
states:
active/hidden |
A
primary partition can have 2 flags enabled or disabled to signify a
certain state. These flags are kept in the partition table in the MBR.
The states are: active/not active/hidden/not hidden. A primary partition
that holds a bootable operating system needs the "active" flag to be
set. Only 1 partition can be set active (which makes sense; you can only
boot 1 operating system at a time). The "hidden" flag is not as
important as it was in the days of Windows 9x: earlier Windows versions
couldn't deal with more than 1 primary partition, so if you had more
than 1 the others had to be "hidden". Windows 2000/2003/XP/Vista have no
problems with 2 or more primary partitions.
These flags can be set with DiskPatch (from the MBR operations
menu). |
| Basic/Dynamic
disks |
A description of disk types that is
used in Windows (2000 and up): a Basic disk contains simple volumes
(using the "old fashioned" partition table to describe partitions), a
Dynamic disk allows for more types of volumes such as spanned/mirrored/raid/striped.
Read more in the Microsoft knowledge base (link).
Added confusion: the elements of a dynamic disk are usually referred to
as "volumes", while the partitions that are on a basic disk
are usually referred to as "partitions". We can only speculate
as to why this is but it may have something to do with the fact that
partitions have their own partition table entries in the MBR and dynamic
disk volumes do not. After all, it's called a partition table. Although,
it's also been named volume table (but not that often). Confused yet?
Essentially though, volumes and partitions are the same thing. |
| Boot
sector |
The
very first sector of a partition. This sector contains a lot of
information that the operating system needs to be able to use the
partition. If this sector is damaged or deleted, the partition can not
be accessed. |
| FAT |
The
File Allocation Table. A table that is used to keep a record of which
parts of the disk are in use. Only used when a partition is formatted as
a FAT type partition. |
| LBA
address |
LBA
stands for Logical Block Addressing. This is simply a way to identify
each sector on a disk: the first sector on a disk (the MBR) is numbered
0 and all following sectors are numbered sequentially. So a LBA address
is nothing more than a sector number. Keep in mind that the count starts
at 0; LBA sector 10 is the 11th sector on the disk. |
| Repairs on Dynamic disks |
| Terminology: |
Description: |
| LDM
database |
A region of the disk that is
claimed by Windows 2000/2003/xp/vista, containing a description of all
volumes on all disks in the system. The LDM database is located at the
end of the disk and is invisible when working with Windows. The LDM is
synchronized to all disks on the system when either volumes are created,
or volumes are added/changed (when using Windows disk manager). The LDM is only created and used when Dynamic disks are used. |
| Type 42h
partition |
When the disks are Dynamic and the
LDM is used to describe the volumes on the disk, Windows creates a
partition type in the MBR that envelopes the entire disk. This way
windows knows that the "old fashioned" partition table is not used
anymore; the LDM is used to identify volumes. |
| MBR |
The Master Boot Record, the first
sector on the disk. Contains the partition tables (a list that describes
the locations of partitions on the disk). |
| Basic/Dynamic
disks |
A description of disk types that is
used in Windows (2000 and up): a Basic disk contains simple volumes
(using the "old fashioned" partition table to describe partitions), a
Dynamic disk allows for more types of volumes such as spanned/mirrored/raid/striped.
Read more in the Microsoft knowledge base (link).
Added confusion: the elements of a dynamic disk are usually referred to
as "volumes", while the partitions that are on a basic disk
are usually referred to as "partitions". We can only speculate
as to why this is but it may have something to do with the fact that
partitions have their own partition table entries in the MBR and dynamic
disk volumes do not. After all, it's called a partition table. Although,
it's also been named volume table (but not that often). Confused yet?
Essentially though, volumes and partitions are the same thing. |
| Boot sector repair with DiskPatch |
| Terminology: |
Description: |
| Boot
sector |
The
very first sector of a partition. This sector contains a lot of
information that the operating system needs to be able to use the
partition. If this sector is damaged or deleted, the partition can not
be accessed. |
Partition
types:
formatted as FAT/NTFS/etc. |
A
partition needs to be formatted before it can be used. Different
operating systems offer/require different format types:
DOS and older Windows versions (9x/ME) use a FAT type format. Newer
Windows versions (NT/2000/2003/XP/Vista) can also use NTFS type formats
(NTFS is preferred, it is more reliable than FAT). Other operating
systems use different formats: Linux uses EXT2/EXT3, OS/2 uses HPFS,
etc.
NTFS stands for New Technology File System. |
| FAT |
The
File Allocation Table. A table that is used to keep a record of which
parts of the disk are in use. Only used when a partition is formatted as
a FAT type partition. |
| Boot
code |
Both the MBR and a
boot sector can contain a small "program" that allows the operating
system to find the stuff that is needed to boot. This "program" (boot
code) is only required if one partition is an active primary partition,
and if an operating system is booted from that partition. The boot code
in the MBR differs from the boot code in a boot sector; the MBR's boot
code is needed to find the partition that has to be booted (this boot
code is used by the computer's BIOS), the boot sector's boot code is
needed to find the necessary files on that partition (this boot code is
used by the operating system). Since the boot code in the boot sector is
used by the operating system, it is different for each operating system. |
| "Fdisk
damage" |
When a FAT
partition is deleted, people sometimes recreate the partition (using
fdisk or a similar tool) in the hope that it will then show up again.
This is not the case. This procedure actually damages the FAT area and
requires additional repairs to make the partition accessible again.
DiskPatch can detect and repair this damage. |
| Root
cluster |
The cluster in the
partition that contains the start of the root directory. Only applicable
to FAT32 partitions. The location of the root cluster is needed to rebuild
a damaged boot sector. |
| MFT |
The Master File
Table. A structure on a NTFS formatted partition that contains
information on where files and other important NTFS structures can be
found. If this structure is damaged the partition will be inaccessible.
In general, the MFT can not be repaired. If MFT damage exists,
file-oriented recovery should be used (copy files from the damaged
partition using a file recovery tool like iRecover). |
|