Step 1: Prepare a disc or drive. To create a bootable disk of EaseUS Partition Master, you should prepare a storage media, like a USB drive, flash drive or a CD/DVD disc. Correctly connect the drive to your computer. Launch EaseUS Partition Master, go to the 'WinPE Creator' feature on the top.
The partition table of a disk cuts it into 'logical disks'.There are several reasons for wanting to do this.Old versions of DOS as well as Windows 95 do not supportfilesystems larger than 2 GB, so partitioning is requiredto break this '2 GB barrier'.Different partitions may carry different operating systemsor different filesystems (FAT, HPFS, NTFS, ext2, ..) to be used by oneoperating system. Sometimes small partitions are used for special purposes(OS/2 Boot Manager uses a small partition for itself, various laptopshave a 'hibernation' partition where the state of the system is storedwhen it goes asleep). Some 'reliable' systems have backup partitions.For backup purposes, say to tape, it is often convenient to havepartitions of a size such that the entire partition can be writtento a single tape.
It is a good idea to keep your own things (say under /home)and privately installed packages (say under /usr/local)separate from the software installed from a distribution.In case these are on a different partition, it is easierto do a complete reinstall (or switch to a different distribution)without losing your own stuff.
For well-designed systems it is often possible to have all basicsystem software on a read-only partition, thus diminishing the probabilityof corruption and saving backup time.There is also a security aspect; for example on a Unix system onemight mount all filesystems other than the root filesystem 'nosuid,nodev',and have /tmp, /home, /var not on the root filesystem, to minimize thepossibility that some suid program is tricked into overwriting avital system file via a hard link to it.
Finally there is the old BIOS problem that can make it impossible to boota system that lives past cylinder 1024. This may mean that one has tohave a partition that ends before the 1024 cylinder limit where thestuff needed at boot time is stored.
One may have an arbitrary number of partitions on a disk.However, the Master Boot Record (MBR, sector 0 of the disk)only holds descriptors for 4 partitions, called the primarypartitions. Usually the BIOS can boot only from a primary partition.(Of course it can boot a boot loader that itself is able to accessnonprimary partitions or other disks.)The descriptors for the remaining partitions, called logical partitions,are scattered along the disk in a linked list of partition table sectors,starting with the MBR.
Each partition table sector contains 4 partition descriptors.A partition descriptor may be of type 05 (DOS extended partition),0f (W95 extended partition), 85 (Linux extended partition),or c5 (DRDOS/secured extended partition),in which case it points to another partition table sector.In this way, we obtain a quaternary tree of partitions.Linux accepts 85 as a synonym for 05 - this is useful if onewants to have extended partitions past the 1024 cylinder limit(to prevent DOS fdisk from crashing or hanging).Windows 95 uses 0f for LBA mapped extended partitions.Thus, an extended partition is not a partition containing data,but is a box containing other partitions.Nevertheless, the partition table sector that starts an extended partitionhas enough room left to contain a boot loader like LILO, so that it ispossible to boot an extended partition.
Most operating systems severely restrict the accepted trees.Usually branching is not allowed, and one gets a linear chain ofpartition table sectors.Linux will accept several extended primary partitions.
A partition table entry is 16 bytes long and contains 6 items(not listed in order).1. A byte that is 0x80 or 0 denoting 'bootable' or not.The standard DOS MBR will not boot a partition unless it is the uniquebootable primary partition. For nonprimary partitions this byte isunused. 2. A byte that gives the type.3. A 4-byte starting sector number.4. A 4-byte length (in sectors).5. A 3-byte starting sector given in C/H/S (cylinder/head/sector) format.6. A 3-byte final sector given in C/H/S format.Linux only uses items 2-4, and hence is not interested in the 'geometry'of the disk, and can use disks with up to 2^32 sectors (2 TiB).DOS uses 5-6 instead of 3-4, and this leads to the well-known problemswith geometry, with the 1024 cylinder limit, the 500 MB limit, the 8 GBlimit. For some details, see thelarge disk HOWTO.
For an extended partition, only the first sector is important -it contains the descriptors for its logical partitions.There are various conventions about how the descriptor of anextended partition (different from the outer one) should look like.There is the paradigm of 'nested boxes', where each extended partitioncovers a disk area containing all the logical partitions inside.There is also the paradigm of 'chained boxes', where each extendedpartition (except possibly the outer one) just contains the nextlogical partition.I don't know which systems follow which paradigms.(David A. Burton <dburton@burtonsys.com> reportsthat System Commander uses the nested style.)However, for the outer (primary) extended partition it is commonto contain all logical partitions inside (i.e., have a start and lengthfield that describes a piece of the disk that contains all logicalpartitions).Of course the 'chained boxes' paradigm is more flexible since itallows logical partitions with a primary partition in between.
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The OS/2 Boot Manager does not want you to have more than oneprimary DOS partition (MS-DOS itself does not mind), and willchange the type from 01, 04, 06, 07to 11, 14, 16, 17.
Also other programs or systems use this 'partition hiding'.For example, System Commander will OR the type with 0x10,changing the Linux 83 into the Amoeba 93.
Some partition IDs imply a particular method of disk access.In particular, IDs 0c, 0e, 0f(the LBA versions of 0b, 06, 05)go with partition table entries that have C/H/S = 1023/255/63and expect access via the extended INT-13 functions (AH=4x)of the BIOS.
The OS/2 Boot Manager MBR code tests whether the extended INT-13 functionsare present, and if so sets memory location 0030:0000 to 'I13X',and otherwise to 0. If the MBR contains other boot code then OS/2no longer boots anything past the 1024 cyl mark.
Some systems use a filesystem that is fully compatible witha standard FAT12 or FAT16 partition, except for using asector size larger than the usual 512 bytes, up to 8192 bytes.This is what is meant by 'logically sectored FAT' in the above.
Logically sectored FATs have been a way to circumvent the dreaded 32 MBpartition size limit before the introduction of DOS 3.31. Since thecount of sectors was restricted to 16-bit on FAT16 (type 04h) the onlyway to grow the partition above the 32 MB limit in a reasonably compatiblefashion was to increase the sector size instead. Physical sectors atROM BIOS INT 13h level are always 512 bytes in size, but other devicesmay require support for other sector sizes in the operating system.Hence, when DOS logs in drives during bootstrap it will record thesector size values indicated in each partition it finds and if itis larger than the previously recorded value, it will slide up themaximum supported sector size to the found value. Very old DOS versionsseem to have started with an initial value of 128 (showing someCP/M heritance here), but recent DOS versions use an initial valueof 512 bytes. Once DOS has logged in all drives (including thosenot represented on INT 13h level, for example, SCSI disk, RAM diskor such), it will set up its internal buffering logic to use themaximum sector size found. This mechanism is present in allDOS versions (although it was partially broken in DOS 5.0 - 6.22).
(Matthias Paul)
People often recommend the undocumented DOS command FDISK /MBRto solve problems with the MBR. This command however does notrewrite the entire MBR - it just rewrites the boot code, the first446 bytes of the MBR, but leaves the 64-byte partition informationalone. Thus, it won't help when the partition table has problems.Moreover, it can be dangerous to restore the boot code to itsoriginal state:if the cause of the problems was a boot sector virus, thenvital information may have been stored elsewhere by the virus,and killing the virus may mean killing access to this information.(For example, the stoned.empire.monkey virus encrypts the originalMBR to sector 0/0/3.)However, people who want to uninstall LILO, and do not know thatLILO has a -u option, can use FDISK /MBR for this purpose.
In a Linux environment, one can wipe all of the MBR with a commandlike 'dd if=/dev/zero of=/dev/hda count=1 bs=512'.If only the boot code must be removed, but not the partition table,then 'dd if=/dev/zero of=/dev/hda count=1 bs=446' will do.Be very careful with such commands. Usually one regrets them later.
As we saw, the structure of the MBR (Master Boot Record, sector 0)is as follows:First 446 bytes boot loader code, then 64 bytes partition table(starting at offset 0x1be = 446), finally 2 bytes signature 0xaa55.
Just before the partition table some operating systems save someinteresting stuff. For example, DRDOS stores a password startingat offset 0x1b6.
Windows NT stores a 4-byte 'disk signature' or 'volume ID' or'Drive Serial Number' starting at offset 0x1b8. It is used to mapdrive letters to disks:in the HKEY_LOCAL_MACHINESYSTEMMountedDevices registry itemthe drive letter is coupled with this disk signature.It is used as a disk label to map disk info to disksin the HKEY_LOCAL_MACHINESYSTEMDISK registry item.This signature is generated by the Disk Administrator when itinitializes the disk, unless there already was a nonzero value there.Also Windows 2000 and Windows XP and Linux use this ID.
NetBSD has a magic word 0xb5e1 at offset 0x1bc to indicate thatthe boot selector area 0x190-0x1b7 (400-439) is valid.Earlier, the NetBSD boot selector area was at offsets 404-443and the signature word was 0xaa55. The area was moved to avoid conflictwith the Windows NT Drive Serial Number.(Problem: Grub preserves this signature, but overwritesthe NetBSD boot selector area.)This area contains a 1-byte default key scancode, a 1-byte flags word,a 2-byte timeout (18.2/sec), and a 36-byte table with the boot selectormenu entries for the 4 primary partitions(four times 8 bytes + terminating NUL).
Grub had a 4-byte stage2 start address at 0x1b8, and a 2-byteversion at 0x1bc, but recent versions preserve 0x1b8-0x1bd.Also LILO v20 and later preserves this area.
Amilo M3438G notebooks have an 'Instant on' button that bootsa 'Power Cinema' interface that runs on top of Linux.It is reported that bytes 0x1b2-0x1b5 are related to thisfeature, and should contain 'PCML'. It is unknown how thepartition to boot is selected.
Some operating systems are reported to have 8 instead of 4partition descriptors in the MBR. Cf. AST DOS under 14and NEC DOS under 24 above.
As mentioned above, the DOS MBR boot code will boot the(unique) primary partition that has been marked active.Usually, in a multi-boot situation, the boot manager togglesthe active bit of the partition that is to be booted.PTS chose a different solution.
Matthias Paul writes:'So far the only DOS being able to boot out of a logical drivein an extended partition is PTS-DOS by use of so called'Advanced Active Partition' entries in the MBR. In order toremain as compatible as possible with existing DOS standards,this works a little bit different and requires a special 5thpartition entry in front of the other four entries in the MBRand corresponding AAP-aware MBR bootstrap code. If the MBRcontains a special AAP signature and this special entry existsand is flagged bootable, the MBR will use this instead of oneof the other four entries. The entry may either point to thebootsector of a logical drive or to a 512 bytes long file(with system-attribute, so it won't be moved around duringdisk defragmentation) somewhere inside the filesystem, whichmakes up a boot sector (same 'IBM' signature, same load address,same register interface). In contrast to the usual MBR code,this MBR code interprets the boot flag byte as physical driveunit (80h.FEh), instead of using it only as a active flag(80h or 00h in older DOS issues or bit 7 set or cleared innewer DOS issues). This way, the AAP MBR could even load aboot sector from other than the first harddisk.'
DOS uses drive letters A: and B: for floppy disk drives, andassigns drive letters C: .. Z: in the order: first all primaryDOS partitions on the first disk, then all primary DOS partitionson the second disk, .., then all logical DOS partitions on firstdisk, etc. DOS will stop investigating logical partitions in a givenextended partition as soon as a non-DOS partition is encountered.(DOS recognizes partition types 1, 4, 6 and 5 for extended.)
Systems like Windows 95, Windows 98, Windows NT, Windows 2000 and OS/2follow a similar convention, but recognize different partition types.Thus, a drive can have a different drive letter for each of theseoperating systems. For details, see the Microsoft KnowledgeBase, e.g.Drive letters in Windows NT,Drive letters in Windows 2000 for unsupported partition types.
DRDOS 6 is reported to assign D: to your third floppy (e.g. Zip) drive,if you have one, while all other versions of DOS would putfurther removable drives at the end of the list.
DRDOS 7.03 is reported to assign drive letters in the order:first active DOS primary on the first disk, then active DOS primaryon the second disk, .., then all logical DOS partitions on firstdisk, then all logical DOS partitions on second disk, ..,then the nonactive DOS primaries on the first disk, ..
The partition table describes the location of partitions bothin 1-dimensional ('LBA') and in 3-dimensional (CHS) form.The former is easy enough, as long as the number of sectorsfits in a 4-byte integer, but for the latter one needs toknow the disk geometry. Note that these days this geometryis entirely fake, and different systems use different fakedgeometries for the same disk, giving lots of problems.(For example, a modern disk may have 2 or 4 heads, but willprobably report 15 or 16 heads to the BIOS, which in turn mayreport 255 heads to DOS or Windows.)
At most 65536 cylinders (numbered 0-65535), 16 heads (numbered 0-15),255 sectors/track (numbered 1-255), for a maximum total capacity of267386880 sectors (of 512 bytes each), that is, 136902082560 bytes (137 GB).
At most 1024 cylinders (numbered 0-1023), 256 heads (numbered 0-255),63 sectors/track (numbered 1-63) for a maximum total capacity of8455716864 bytes (8.4 GB). This is a serious limitation today.It means that DOS cannot use present day large disks.
If the same values for c,h,s are used for the BIOS Int 13 call andfor the IDE disk I/O, then both limitations combine, and one canuse at most 1024 cylinders, 16 heads, 63 sectors/track, for amaximum total capacity of 528482304 bytes (528MB), the infamous504 MiB limit.This was already a problem many years ago, and all kinds of software,firmware and hardware solutions were invented. On the software side,there are Disk Managers, that circumvent the BIOS and go directly tothe hardware. On the firmware side there are translating BIOSes,that use one geometry when talking to the disk, and another onewhen talking to the user program. (At best, this again allows accessto 8.4 GB.) On the hardware side, there is LBA disk access,that no longer uses (c,h,s).
Some older BIOSes only allocate 12 bits for the field in CMOS RAM thatgives the number of cylinders. Consequently, this number can be at most4095, and only 4095*16*63*512=2113413120 bytes are accessible.
There was a bug in the Phoenix 4.03 and 4.04 BIOS firmware that wouldcause the system to lock up in the CMOS setup for drives with a capacityover 3277 MB.
Simple BIOS translation (ECHS=Extended CHS, sometimes called 'Large disk support' or just 'Large')works by repeatedly doubling the number of heads and halving the numberof cylinders shown to DOS, until the number of cylinders is at most 1024.Now DOS and Windows 95 cannot handle 256 heads or more,and in the common case that the disk reports 16 heads, this means thatthis simple mechanism only works up to 8192*16*63*512=4227858432 bytes(with a fake geometry with 1024 cylinders, 128 heads, 63 sectors/track).Note that ECHS does not change the number of sectors per track, so ifthat is not 63, the limit will be lower.
Slightly smarter BIOSes avoid the previous problem by first adjusting thenumber of heads to 15 ('revised ECHS'), so that a fake geometry with240 heads can be obtained, good for 1024*240*63*512=7927234560 bytes.
Finally, if the BIOS does all it can to make this translation a success,and uses 255 heads and 63 sectors/track ('assisted LBA' or just 'LBA')it may reach 1024*255*63*512=8422686720 bytes, slightly less than theearlier 8.4 GB limit because the geometries with 256 heads must be avoided.(This translation will use for the number of heads the first value Hin the sequence 16, 32, 64, 128, 255 for which the total disk capacityfits in 1024*H*63*512, and then computes the number of cylinders C astotal capacity divided by (H*63*512).)
Large disks report 16 heads, 63 sectors/track and 16383 cylinders.Many BIOSes compute an actual number of cylinders by dividingthe total capacity by 16*63. For disks larger than 33.8 GB thisleads to a number of cylinders larger than 65535. Now the BIOScrashes or hangs. The solution is to upgrade the BIOS. If that isimpossible, it sometimes helps to take the disk out of the BIOS,but that won't work if one has to boot from the disk, and may alsofail because the BIOS already hangs during initial probing.Usually one can use a jumper to make the disk appear smaller.Also many operating systems have problems - only the most recentversions work with these disks.
As already noted, the old ATA specification does not allow accessto all of a disk that is larger than 137 GB. Indeed, it uses only28 bits to specify a sector number. However, ATA-6 defines an extensionwith 48-bit sector number. The first disks needing the extension wereMaxtor 160 GB disks, that came to market in Fall 2001.
Hard drives over 8.4 GB are supposed to report their geometry as 16383/16/63.This in effect means that the 'geometry' is obsolete, and the total disksize can no longer be computed from the geometry.
Of course various operating systems and file system types have their ownlimits, in addition to those mentioned above.
Early MSDOS filled the partition table starting at the end.In particular, in the case of only one partition, the descriptorwas stored in the fourth primary slot. These days DOS FDISKstarts at the beginning, but other systems, like Unixware, stillstart at the end.Also Iomega writes the single partition of a ZIP diskin the last entry (so that it has to be mounted as /dev/sda4 or/dev/hdc4 or so).
MSDOS 6.22 FDISK creates the four entries in the partition table sectorthat starts an extended partition as 1. a data partition (or empty),2. the next extended partition, 3. and 4. empty.(But old versions of MS-DOS start at the end, and first fill entry 4.)If the first logical partition (that is not the last one) is removed,only the link in position 2 remains.An extended partition table sector can describe only a singledata partition (the first one encountered). When reading a table,FDISK accepts the entries in any order and position, but it willwrite the sector normalized as described.
DRDOS on the other hand expects zero to four entries in an extendedpartition table sector. Data partitions,possibly followed by the link to the next extended partition.Thus, this link is always the last significant entry, and willbe the first entry if there is no data partition (becauseit has been deleted).
Many systems are willing to accept more than two nonempty partsin an extended partition, but will not create such themselves.
It is rumoured that the outer extended partition should be the 4thin the MBR, but I don't know any systems that have this restriction.DRDOS FDISK always puts the extended partition in the fourth entryno matter how many other entries you may have.
MSDOS fdisk shows 4 primary partitions, and of the logical partitionsonly those that have a DOS type (1, 4 or 6). It will list the type ofa logical partition as 'Unknown' if the partition is not formatted.
It is rumoured that DRDOS ignores the high-order bit of the ID(and that is the reason for the additional Linux IDs 41, 42, 43),but I don't know whether that is true (and for which versions of DRDOS).It is also rumoured that DRDOS will write 1 sector past the endof a partition - I have never seen this either. Confirmation?It is however true, that DRDOS fdisk only looks at the last 4 bitswhen printing a type, so that types 11, 21, etc are printed as DOS 2.0,but such types are not acceptable for DRDOS itself.
The OS/2 Warp fdisk is very instable, and hangs or crashes withgeneral protection fault as soon as the partition table is somewhatunusual, cf. Cannot set an installable partition with FDISK.
The Windows NT Disk Administrator will corrupt your diskwhen it writes a signature on a disk with two or morelogical partitions. SeeDisk Administrator Corrupts Partitions.
Antoine reports that if the last partition in a chain of logical partitionsis of a type unknown to DOS then the DOS partition table parser may leavedata about it in its drive letter table and confuse this non-DOS logicalpartition with the next partition (maybe logical on another disk, or nonactiveprimary). This can cause data loss.
The use of Win95/Win98 FDISK in a mixed system is dangerous.It will delete a non-FAT logical partition when you had actuallytold it to delete a FAT partition somewhere farther down the chainof logical partitions. SeeCannot View NTFS Logical Drive After Using FDISK.
The system partition in Windows NT 4 must be contained in the first7.8 GB of the disk (or less, in case the BIOS geometry does not have255 heads and 63 sectors/track; the actual restriction is that all of itmust be accessible using BIOS Int 13).It must not be larger than 4 GB because Windows NT 4 first installsinto a FAT16 partition and then converts it into NTFS duringthe second phase of the installation.It must start before the 4 GB mark (bug fixed in Service Pack 5).SeeWindows NT 4.0 Supports Maximum of 7.8-GB System Partitionand Windows NT Partitioning Rules During Setupand Boot Partition Created During Setup Limited to 4 Gigabytesand Windows NT Does Not Boot to a Partition That Starts More Than 4 GB into Disk.
Windows NT and Windows 2000 use for SCSI disks whatever the BIOS says(usually C/H/S=C/255/63) for the boot drive, and C/64/32for all other SCSI drives. SeeHow Windows NT Handles Drive Translation.
Windows 2000 seems to require that the partition order agreeswith the disk order.
The OS/2 fdisk writes some strange length in the descriptor of thelast extended partition. This is probably a bug.OS/2 fdisk fails to update the length of the (outer) extended partitionwhen a primary partition is created in the free space (space not usedby a logical partition) at the end of this extended partition.This can lead to overlapping partitions.
OS/2 FDISK does not know about type f, but accepts DOS Extended Partitionsextending beyond cylinder 1023. When some other partition handler,like Partition Magic 4.0, changes the type of a large extendedpartition from 05 to 0f, OS/2 loses access.
OS/2 Boot Manager keeps a private copy of the partition table data.This leads to problems when changing the partition tablewith 3rd party tools.
Windows 2000 tries to destroy OS/2 Boot Manager. Upon boot it ignoresthe 0a partition ID, and sees something resembling a FAT boot sectordescribing 2 FAT copies. When FASTFAT.SYS marks this partition as cleanin the first reserved FAT entry, the mirror (2nd) FAT sector is also updated.However, there is no mirror FAT, and FASTFAT.SYS writes into the middle ofthe OS/2 Boot Manager code. This aggression was built into FASTFAT.SYSat a fairly late stage, and prerelease versions work without problems.See also kb/q265003.Update both WINNTSYSTEMDRIVERSFASTFAT.SYS andWINNTSYSTEMDLLCACHEFASTFAT.SYS .
Windows XP understands the OnTrack Disk Manager ID 54.It was reported that a custom partition that happened to use ID 54was corrupted by Windows Disk Manager: it wrote a partition table entryto sector 0 of that partition, absolute sector 63 on disk,at offset 0x1be, and a disk serial number just before that.
Then there is the problem of what to write in(c,h,s) if the numbersdo not fit. The main strategies seem to be
1. Mark (c,h,s) as invalid by writingsome fixed value.
1a. Write (1023,255,63) for any nonrepresentable CHS.
1b. Write maximum valid values, typically (1023,254,63),for any nonrepresentable CHS.
1c. Write (1022,254,63) for any nonrepresentable CHS.
1d. Write (1023,0,1) for the begin CHS of a partition thatstarts at or past cylinder 1024, and write (1023,255,63) for the end.
1e. Write (1023,0,1) for the begin CHS of a partition thatstarts at or past cylinder 1024, and write (1023,254,63) for the end.
2. Leave h, s but do something to c.Of course, these fail if h or s does not fit.
2a. Truncate c to 1023, writing(1023, #heads-1, #sectors).
2b. Truncate c to 1022, writing(1022, #heads-1, #sectors).
2c. Reduce c mod 1024, writing only its last 10 bits.
Windows is said to follow 1a.OS/2 is said to follow 1b.Solaris 8 follows 1c or 2b.Andreas Jellinghaus reports that Partition Magic follows 1dand detects a problem if start CHS is set to (1023,255,63).Jan van Wijk's pcpartit.pdf reports that Partition Magic follows 1e.Jeff Merkey reports that Novell Netware follows 2b.He writes: If you do not use their methods on NetWarepartitions, NetWare will not recognize the partition entries correctly,and will attempt to reinitialize the entire partition table on a systemif they are wrong (Ouch!).Some versions of Linux fdisk used 2a or 2c, and this confuses OS/2 fdisk - cf.Linux, OS/2 and >1024 Cylinder HDDs.David A. Burton <dburton@burtonsys.com> reportsthat System Commander Deluxe (from V Communications) uses:
1f. Mark (c,h,s) as invalid by writingc=1022.(Maybe this is really 2b?)
A very convenient tool for manipulating partitions is Partition Magic,a commercial program from PowerQuest. Below a description of some ofits error numbers. (The URL that gave this information no longer exists.)This is of interest also for those who do not have this program: it indicateswhat conditions the PowerQuest people think a partition table should satisfy.
(Not all of these conditions are complied with by DRDOS or OS/2 or Linuxor Windows NT on Alpha, so a partition manipulator should accept a muchwider range of partition tables, but such a program might try to followthese rules when creating partitions.)
The MBR or some EPBR contains two extended partitions.(PowerQuest uses the acronym EPBR for a link in the chain ofextended partition table sectors.)(Linux comment: there are three partition types indicating anextended partition, namely 0x5, 0xf, 0x85. DOS only recognizes the first.Recent Windows only recognizes the first two. Linux will accepttwo or more extended partitions in the MBR, and often it is usefulto have a 0x5 chain for use by DOS (where this chainstays below the 1024 cylinder boundary) and a 0x85 chain for use by Linux.Nothing is wrong with having both 0x85 and one of 0x5, 0xf in the MBR.However, it is bad to have both 0x5 and 0xf. This is sometimes seen whenpeople use some fdisk-type program that does not yet know about 0xf on adisk that already contains such an extended partition.)(DRDOS comment: extended partition types 0xc5 and 0x5 can coexist.)
The LBA Number of sectors value in the partition table is 0.
The Head value of CHS begin is not 0 or 1.PartitionMagic expects all FAT, HPFS and NTFS partitions to startand end on cylinder boundaries.(Comment: Windows NT on Alpha does not comply with this rule, andcan create partitions starting on arbitrary sectors. There is noknown operating system that requires this restriction. However,there exists software that tries to guess the disk geometry bylooking at the CHS start and end values in a partition table.Note that with large disks CHS values are entirely meaningless.)
The Sector value of CHS begin is not 1. (Same comment.)
The Cylinder value of CHS begin is larger than the numberof cylinders that the BIOS reports.(Comment: Usually this means that programs or operating systemsthat use the BIOS cannot use this partition. It may help tochange the BIOS translation. For Linux it does not matter,except that the /boot partition containing LILO stuffshould be accessible.)
The Head value of CHS end is not one less than the number ofheads that the BIOS reports, or the Sector value of CHS endis not equal to the number of sectors per track that the BIOS reports.(See above under 105.) Deep blue sea 1999 full movie.
The Cylinder value of CHS end is larger than the numberof cylinders that the BIOS reports.
(Comment: the model here is that the extended partition is onebig box, taking a consecutive piece of disk area, containingthe logical partitions. Linux allows the logical partitionsto be anywhere on the disk, also with primary partitions in between.)
A partition ends past the start of another. If the filesystemsdon't actually overlap, which they rarely do, then this can befixed by truncating the overlapping partition.(Sometimes overlapping partitions are created by OS/2 fdisk:if there is still room in an extended partition it allows the creationof a primary partition that overlaps the end of the extended partition.Now if someone afterwards creates a logical partition inside theextended partition, data loss might occur.)
If the EPBR is found at sector N, and there are 63 sectors per track,then Partition Magic expects the logical partition to start at sectorN+63.
(Comment: Partition Magic expects the extended partition to bea big box containing a chain of pairwise disjoint boxes.Here each logical partition except for the first one has thesame ending sector as the surrounding box.Another model one finds is a big box containing a smallerbox, containing a smaller box .. In that model all EPBR extendedpartition entries will show the same end sector.In reality the end sector of an EPBR does not play a role anywhere.)
PowerQuest states: DOS, OS/2, Windows 95 and Windows NT requirethat logical partitions occur in the chain in the on-disk order.(Comment: Linux does not require this. However, reordering thelinks in the chain is trivial (for example with sfdisk). Notethat disk names will be different after reordering.)
A lot of useful information was supplied by various people:Thomas Wolfram (thomas@aeon.in-berlin.de) - the author of os-bs,Peter Gutmann (pgut01@cs.auckland.ac.nz) - the author of SFS,Cody Batt (codyb@powerquest.com),Christian Carey (ccarey@CapAccess.ORG),Dan Fandrich (dan@fch.wimsey.bc.ca),David Faulks (david@santana.ca),Kai Henningsen (kai@khms.westfalen.de),Dan Hildebrand (danh@qnx.com),Todd Larason (jtl@molehill.org),Mark Morgan Lloyd (markMLl.in@telemetry.co.uk).Marek Michalkiewicz (marekm@i17linuxb.ists.pwr.wroc.pl),David C. Niemi (niemidc@clark.net),Piotr Niemiec (PNiemiec@compuserve.com),Matthias Paul (Matthias.Paul@post.rwth-aachen.de),Loek Weerd (loekw@worldonline.nl),S. Widlake (s.widlake@rl.ac.uk),Gareth Randall (gareth.randall@virgin.net).