109:— and a substantial market in third-party controllers and drives resulted in significant inconvenience, since a Unix system's operators would have to recompile the kernel in order to add an appropriate partition layout for every different disk they attached to a system. This also presented a problem for commercially licensed Unix vendors, as support engineers would have to recompile the kernel before installing upgrades on a customer's machine. For the 4.3-Tahoe release, which supported a non-
133:, in the first sector or track of the disk, where the computer's firmware expected a boot loader to be. Having the label embedded in the boot loader meant that the loader did not itself need to contain code to locate and read the label from the disk. However, this system only works when the computer firmware simply loads and executes the boot loader without attempting to determine whether it is valid. In the world of
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In historic Bell Labs and BSD Unix releases, disk partitioning was fixed, compiled into each device driver at the time the kernel was compiled. The fixed partitions overlapped, allowing the disk to be used with different layouts by careful selection of a non-overlapping subset of the partitions.
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Partition 'c' overlaps all of the other partitions and describes the entire disk. Its start and length are fixed. On systems where the disklabel co-exists with another partitioning scheme (such as on PC hardware), partition 'c' may actually only extend to an area of disk allocated to the BSD
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The same PC hard drive can have both BSD disklabel partitions and the MS-DOS type logical partitions in separate primary partitions. FreeBSD and other BSD operating systems can access both the BSD disklabel subdivided partition and the MS-DOS type
Extended/Logical partitions.
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BSD disklabels traditionally contain 8 entries for describing partitions. These are, by convention, labeled alphabetically, 'a' through to 'h'. Some BSD variants have since increased this to 16 partitions, labeled 'a' through to 'p'.
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Partition Table scheme instead, and the BSD partitioning scheme is nested within a single, primary, MBR partition (just as the "extended" partitioning scheme is nested within a single primary partition with
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121:(8) command. (Such on-disk partition maps were already well known on other operating systems, and only the specific format, not the fact of partition labels generally, was invented by Berkeley.)
216:. The boot code in the Volume Boot Record containing the disklabel is thus simplified, as it need only look in one fixed location to find the location of the boot volume;
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This article is about the "disklabel" data structure used in BSD-derived operating systems. For the "name" given to a specific volume in FAT (and other) filesystems, see
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This was not originally viewed as a problem because there were only a small number of disk drives supported by each driver, and Unix only ran on one vendor's hardware.
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and the subdivisions of a primary MBR partition (for the nested BSD partitioning scheme) that are described by its disklabel are called
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This format has a similar goal as the extended partitions and logical partition system used by MS-DOS, Windows and Linux.
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The MBR partition IDs for primary partitions that are subdivided using BSD disklabels are
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150:). Sometimes (particularly in FreeBSD), the primary MBR partitions are referred to as
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Partition 'a' is the "root" partition, the volume from which the operating system is
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416:(2nd ed.). Upper Saddle River, New Jersey: Addison-Wesley. p. 377.
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operating system, and partition 'd' is used to cover the whole physical disk.
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Also by convention, partitions 'a', 'b', and 'c' have fixed meanings:
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Traditionally, the disklabel was embedded in the first-stage
388:. Reading, Massachusetts: Addison-Wesley. pp. 199–200.
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utility. In later versions of FreeBSD, this was renamed as
77:-Tahoe release. Disklabels are usually edited using the
412:; Neville-Neil, George V.; Watson, Robert N.M. (2015).
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that contains information about the location of the
97:The introduction of standardized disk interfaces —
438:Change legacy MBR partition type from 0xA5 to 0x6C
73:on the disk. Disklabels were introduced in the
137:, disks are usually partitioned using the PC
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158:. The BSD disklabel is contained within the
53:) and in related operating systems such as
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344:"FreeBSD/i386 5.1-RELEASE Release Notes"
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7:
16:Disklabel for BSD operating systems
455:"Understanding FreeBSD Disklabels"
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256:Boot Engineering Extension Record
286:OpenBSD manual pages, section 5
436:DragonFly BSD commit 794d80a:
162:of its primary MBR partition.
1:
111:Digital Equipment Corporation
486:Unix file system technology
125:Where disklabels are stored
502:
319:4.4BSD Programmer's Manual
200:The contents of disklabels
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143:master boot record (MBR)
61:is a record stored on a
410:McKusick, Marshall Kirk
370:McKusick, Marshall Kirk
219:Partition 'b' is the "
171:(386BSD and FreeBSD),
148:extended boot records
250:GUID Partition Table
244:Extended Boot Record
382:Quarterman, John S.
262:Apple Partition Map
63:data storage device
453:Michael W. Lucas.
378:Karels, Michael J.
238:Master Boot Record
160:volume boot record
135:IBM PC compatibles
423:978-0-321-96897-5
294:"Using disklabel"
189:(DragonFly BSD).
35:operating systems
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457:. Archived from
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321:. Archived from
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268:Rigid Disk Block
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461:on 2017-06-23.
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315:"disklabel(5)"
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183:(NetBSD), and
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115:CCI Power 6/32
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374:Bostic, Keith
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325:on 2013-12-24
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51:DragonFly BSD
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476:BSD software
459:the original
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347:. Retrieved
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327:. Retrieved
323:the original
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223:" partition;
214:bootstrapped
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21:Volume label
298:OpenBSD FAQ
282:"disklabel"
177:(OpenBSD),
37:(including
470:Categories
329:2008-02-28
275:References
156:partitions
71:partitions
65:such as a
119:disklabel
79:disklabel
67:hard disk
59:disklabel
30:-derived
384:(1996).
232:See also
83:bsdlabel
32:computer
89:History
47:FreeBSD
43:OpenBSD
420:
392:
258:(BEER)
152:slices
75:4.3BSD
39:NetBSD
349:9 May
270:(RDB)
264:(APM)
252:(GPT)
246:(EBR)
240:(MBR)
55:SunOS
418:ISBN
390:ISBN
351:2017
221:swap
139:BIOS
107:SCSI
105:and
103:ESDI
57:, a
49:and
186:6Ch
180:A9h
174:A6h
168:A5h
141:'s
99:SMD
28:BSD
26:In
472::
380:;
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372:;
359:^
317:.
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101:,
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45:,
41:,
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23:.
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