maximum partition size using fat16 file system

8/9/2019 Maximum Partition Size Using FAT16 File System

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MS-DOS Partitioning Summary (Q69912)

The information in this article applies to:

Microsoft MS-DOS operating system

Microsoft Windows 95


SUMMARY

This article contains a summary of MS-DOS partitioning information. For information on howMS-DOS assigns drive letters, please see the following article in the Microsoft nowledge

!ase:

"#$%&'Order in (hich MS-DOS )ssigns Drive *etters

) hard dis+s master oot record M!/0 is located in the first sector of the dis+ cylinder 1,side 1, sector $0. The partition tale is located at offset 1$!2, containing up to four $3-yte

entries. The fourth yte of each partition tale entry is used to mar+ the partition type.

MS-DOS egan supporting hard dis+s in version 4.1.

MS-DOS Versions 2!

MS-DOS 4.5 supports one type 1$ partition of up to $# megaytes M!0 in si6e, which usesa $4-it file allocation tale F)T0. Fdis+ creates only one MS-DOS partition per drive.

MS-DOS "#

MS-DOS 7.1 supports partitions larger than $# M! using a $3-it F)T, which allows a

smaller cluster si6e and more efficient dis+ usage. )s a result, MS-DOS 4.5 hard dis+slarger than $# M! are incompatile with later versions of MS-DOS. Fdis+ creates only one

MS-DOS partition per drive.

MS-DOS ""

MS-DOS 7.7 introduces support for more than one logical drive per hard dis+. *ogical drivesare treated as completely separate dis+s under MS-DOS, even though they may occupy the

same physical hard dis+.

This is supported y using nonootale MS-DOS partitions +nown as e5tended MS-DOSpartitions. Fdis+ reports these as 28T DOS9 other MS-DOS partitions are reported as /;DOS for primary MS-DOS0. 2ach primary MS-DOS partition is a logical drive, and e5tendedMS-DOS partitions contain from $ to 47 logical drives MS-DOS supports drive letters up to


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write to the drive instead of the normal BylinderA?eadASectorerTrac+ B?S0 ;@T$7hfunctions ecause the hard dis+ has more than $14> cylinders andAor more than

$3,&$$,3'1 sectors. @ote that earlier versions of FD;S recogni6e these (indows %#partitions as @O@-DOS partitions.

&in'os 9% OM Ser*i+e Re,ease 2 an' &in'os 9

(indows %# O2M Service /elease 4 OS/40 and (indows %' support two new partition

types 1! and 1B0 to support the F)T74 file system. For additional information aout F)T74,please see the following article in the Microsoft nowledge !ase:

)/T;B*2 ;D: "$#>%%&T;T*2 : Description of the F)T74 File System

The partition types supported y OS/4 and (indows %' are as follows:Partition Fdisk Starting in

Type Reports Sie F!T Type "ersion

--------------------------------------------------------------------- #$ PR% DOS #-$5 M& $'-&it MS-DOS '(# #+ PR% DOS $,-' M& $,-&it MS-DOS (# #5 ./T DOS #-' 0& n2a MS-DOS ( #, PR% DOS ' M&-' 0& $,-1it MS-DOS +(# #. PR% DOS ' M&-' 0& $,-1it Windows 95 #F ./T DOS #-' 0& n2a Windows 95 #& PR% DOS 5$' M& - ' tera1ytes '-1it OSR' # ./T DOS 5$' M& - ' tera1ytes '-1it OSR'

Types #. #F and # re7ire e4tended %nt$ spport(
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q154997http://support.microsoft.com/default.aspx?scid=kb;en-us;Q154997


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.A/ /y0e an' ,uster Sie De0en's on 3ogi+a, Dri*e Sie(Q64"21)


Microsoft MS-DOS operating system "ersions ($ (' ('$ ( (a +(# +(#$

5(# 5(#a ,(# ,(' ,('$ ,(''


SUMMARY

MS-DOS allocates dis+ space for files in units of one or more sectors9 these units are calledCclustersC or Callocation units.C On any MS-DOS dis+, a $-yte file is allocated $ cluster ofdis+ space, wasting the unused area of the cluster. ) file that is 7.4 clusters large is given >clusters. Overall, a smaller cluster si6e means less waste.

The cluster si6e for a drive is decided y FO/M)T, depending on the si6e of the logical drivesee tale, elow0. C*ogical driveC refers to an MS-DOS volume accessed y a drive letter

):, !:, B:, D:, and so forth0. ?ard dis+ users may want to consider cluster si6e whenchoosing how to partition their drives0.

The cluster si6e of a floppy drive cannot e changed. The cluster si6e of a hard drive can echanged only y changing the si6e of the logical drive, which is done y repartitioning thehard drive.

B?DS displays the allocation unit si6e for a logical drive. FD;Ss option > displays the

si6es0 of logical drives on the hard drives0.

@OT2: DouleSpace-compressed drives appear to have ' clusters, ut internally vary thesectors-per-cluster as necessary this information is recorded in the MDF)T0. For e5ample,

a $1 file which compresses y a factor of 4:$ actually uses #, or $1 sectors, of drivespace.

MOR 5.ORMA/5O

The following is a tale of logical drive si6es, F)T File )llocation Tale0 types, and clustersi6es:

Dri"e Sie F!T Type Sectors 3ster )3ogica3 "o3me* Per 3ster Sie ---------------- -------- ----------- -------)F3oppy Disks* ,#: $'-1it ' $: ;'#: $'-1it ' $: $(' M& $'-1it $ 5$' 1ytes $(++ M& $'-1it $ 5$' 1ytes '(88 M& $'-1it ' $:)


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$#'+ M& - '#+; M& $,-1it ,+ ':

@OT2S:

Sectors are 5$' 1ytes in sie e4cept on some R!M dri"es(

%n t6e past some O.Ms 6a"e modi=ed t6eir "ersions of MS-DOS to spport ot6ersector and2or c3ster sies( T6e Microsoft MS-DOS 5 >pgrade Setp wi33 if possi13e

con"ert t6e 3ogica3 dri"e to MS-DOS 5(# compati13e( T6is entai3s con"erting t6esector sie to 5$' 1ytes w6i3e retaining t6e nonstandard c3ster sie(

MS-DOS determines t6e F!T sie 1ased on t6e nm1er of c3sters( %f t6ere are +#85or fewer c3sters a $'-1it F!T is sed( %f t6ere are +#8, or more c3sters a $,-1it F!Tis sed(

Ma!imum Partition Sie Using .A/16 .i,e System (Q11""%)


Microsoft Windows Mi33ennim .dition

Microsoft Windows 98 Second .dition




SUMMARY

Microsoft MS-DOS versions >.1 and later allow FD;S to partition hard dis+s up to >gigaytes !0 in si6e. ?owever, the MS-DOS file allocation tale F)T0 file system cansupport only 4 ! per partition. !ecause of this fact, a hard dis+ etween 4 and > ! insi6e must e ro+en down into multiple partitions, each of which does not e5ceed 4 !.

@OT2: (indows %# O2M Service /elease version 4 and later support drives larger than 4

! using the F)T74 file system. For more information aout the F)T74 file system, pleasesee the following article in the Microsoft nowledge !ase:

)/T;B*2-;D: "$#>%%&T;T*2 : Description of the F)T74 File System

MOR 5.ORMA/5O

The 4-! partition limit is imposed y the ma5imum numer of clusters and the largestcluster si6e supported y the F)T file system. The F)T file system is limited to 3#,#4#clusters. The si6e of a cluster must e a power of 4 and less than 3#,#73 ytes--this resultsin a ma5imum cluster si6e of 74,&3' ytes 740. Multiplying the ma5imum numer ofclusters 3#,#4#0 y the ma5imum cluster si6e 74,&3'0 e=uals 4 !.

@ote that the hard dis+ drive must e supported y the computers /OM !;OS );s, which

have a $14>-cylinder limitation, in order for FD;S to partition the hard dis+.

!ecause 74 per cluster can waste valuale hard dis+ space, the F)T file system is not

always the est hard dis+ management scheme. Microsoft (indows @T uses the @T File


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System @TFS0, which uses a different fileAcluster scheme. Microsoft OSA4 version $.7offered ?FS, which also uses a more conservative method of allocating dis+ resources.

@OT2: Microsoft (indows @T also supports F)T drives. (indows @T 7.#$ supports F)Tdrives up to > ! in si6e. F)T drives from 4 ! to > ! in si6e are not supported y MS-DOS or (indows. ;n other words, if you wish to have a F)T drive accessile from MS-DOSor (indows %#A%' and (indows @T, your F)T drive should e no larger than 4 !. ;f you

will e accessing the F)T drive from only (indows @T, then the drive can e 4 ! to > ! insi6e. For additional information, please see the following article in the Microsoft nowledge!ase:


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Pro7,ems A++essing .A/16 Dri*es 3arger /8an 2 :(Q124%1)





Microsoft Windows ?T Workstation "ersions (5 (5$ +(#

Microsoft Windows ?T Ser"er "ersions (5 (5$ +(#

Microsoft Windows Mi33ennim .dition

SUMMARY

Microsoft (indows @T supports the creation of primary partitions and logical drives of up to> gigaytes !0 using the File )llocation Tale $3 F)T$30 file system, ut (indows %#A%'and MS-DOS do not support these drives. The si6e limit for logical drives using the F)T$3file system in (indows %#A%' and MS-DOS is 4 !.

NOTE : (indows %# O2M Service /elease 4 and later support drives larger than 4 ! using

the F)T74 file system. For more information aout F)T74, please see the following article inthe Microsoft nowledge !ase:

)/T;B*2-;D: "$#>%%&T;T*2 : Description of the F)T74 File System

(indows @T >.1 does not support F)T74, ut F)T74 support has een added in (indows4111.

MOR 5.ORMA/5O

Microsoft does not recommend using MS-DOS or (indows %#A%' with a > ! F)T$3 drivecreated in (indows @T. ;f you use (indows @Ts dual oot feature to oot MS-DOS or(indows %#A%', you may e ale to access the drive, ut you may e5perience une5pectedehavior. ;n particular, some programs or utilities may incorrectly report that no free space1 ytes0 e5ists on the drive.

;n addition, you cannot run (indows %#A%' Setup if your computer has a F)T$3 drive

created y (indows @T.

For e5ample, during (indows %' Setup you receive the following error message if yoursystem has a F)T$3 drive larger than 4 !:


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Setup has detected that your hard drive has a 3>-cluster F)T partition.!ecause ScanDis+ does not wor+ on dis+s with this cluster si6e, Setup cannot

continue. To complete Setup, you must repartition your hard drive, formatthe partition with a F)T file system that has a cluster si6e of 74 or less, andthen restart Setup.

Other prolems accessing F)T$3 drives larger than 4 ! in (indows %#A%' may include the

following:

Rnning t6e Defrag too3 on t6e dri"e cases a @Di"ide 1y ero@ error message or t6eDefrag too3 stops responding )6angs*(

ScanDisk for MS-DOS stops responding )6angs* or cases an @Ot of memory@ error

message(

T6e 6kdsk too3 may report m3tip3e @a33ocation errors@ on t6e dri"e(

ScanDis+ for (indows typically runs without error on 3>+ cluster F)T$3 drives and shows3> clustersAallocation units on the Summary dialog.

!oth MS-DOS and the retail release of (indows %# use a $3-it F)T for logical drives largerthan $# megaytes M!0. The ma5imum numer of clusters for a $3-it F)T drive is 3>. ;naddition, the ma5imum cluster si6e for a F)T$3 drive in MS-DOS, or (indows %# is 74.Therefore, the ma5imum logical drive si6e for F)T$3 is calculated as follows:

': 4 ,+: A '#+8 M& A ' 0&

The ma5imum cluster si6e for a F)T$3 drive in (indows %' is 74, or 74,&3' ytes.

Therefore, the ma5imum logical drive si6e for F)T$3 is calculated as follows:': 4 ,+: A '#+8 M& A ' 0&

(indows @T uses a 3> ma5imum cluster si6e to allow drives larger than 4 ! using F)T$3.The ma5imum logical F)T$3 drive si6e in (indows @T is calculated as follows:

,+: 4 ,+: A +#9, M& A + 0&

@OT2: On a F)T drive, space is allocated y clusters. That is, a file that is smaller than the

drives cluster si6e is still allocated one full cluster, thus wasting the additional space in thecluster. Similarly, a file that is large enough to fill 7-$A4 clusters is allocated four fullclusters. Esing a smaller cluster si6e typically results in less wasted space on the drive.

The cluster si6e for a F)T drive is determined when the drive is formatted and variesdepending on the si6e of the logical drive. For more information aout cluster and logicaldrive si6es in MS-DOS, please see the following article in the Microsoft nowledge !ase:

)/T;B*2-;D: "3&74$ "3&74$

T;T*2 : F)T Type and Bluster Si6e Depends on *ogical Drive Si6e


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(indows %# and MS-DOS use the FD;S utility to partition a dis+. (hen it accesses a hard

dis+, FD;S uses the system )T /OM !;OS ;@T$7h interface, which has a ma5imum of$14> cylinders, 4## heads, and 37 sectors per trac+. FD;S can access any drive within thelimits imposed y the )T /OM !;OS, which means that FD;S can access drives of up to '!, calculated as follows:

$#'+ cy3inders 4 '55 6eads 4 , sectors per track 4 5$' 1ytes per

sector A 8+'',8,;'# 1ytes or rog63y 8 0&

The original ;D2 hardware interface is limited to $3 heads, which reduces the ma5imumdrive si6e to #1> M!. @ewer ;D2 )T);0 technology, however, uses a translation schemecalled *ogical !loc+ )ddressing *!)0 to e5ceed the #1> M! limit as imposed y the system)T /OM !;OS and ;D2 specifi- cation. SBS; and 2SD; hard drive controllers use similartranslation methods that are usually uilt into the controller cards /OM !;OS to e5ceed the#1> M! si6e limit. For more information aout the use of large hard dis+s with MS-DOS and(indows %#A%', please see the following article in the Microsoft nowledge !ase:

)/T;B*2-;D: "$43'##T;T*2 : (indows Support for *arge ;D2 ?ard Dis+s

The FD;S utility in MS-DOS and the retail release of (indows %# can create an e5tendedpartition larger than 4 !. FD;S can then create multiple formatted drives of up to 4 ! inthis e5tended partition that conform to the )T /OM !;OS constraints mentioned earlier.FD;S does not, however, allow the creation of a primary F)T$3 partition or logical F)T$3drives in an e5tended partition that is larger than 4 !. @ote also that, as mentionedearlier, logical drives larger than #1> M! cannot e accessed using MS-DOS or (indows %#

unless *!) or geometry translation is used.

;n (indows @T, you can create > ! F)T$3 drives, either as a primary partition or as alogical drive in an e5tended partition. !ecause MS-DOS and (indows %#A%' have ama5imum logical F)T$3 drive si6e of 4 !, F)T$3 drives larger than 4 ! created using

(indows @T cannot e relialy accessed using MS-DOS or (indows %#A%'.

maximum partition size using fat16 file system

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