Editing File Allocation Table (section)

=== <span id="FAT16"></span>Initial FAT16 ===

{{infobox file system
| name                    = FAT16
| developer               = [[Microsoft]], [[IBM]], [[Digital Research]], [[Novell]]
| full_name               = [[Design of the FAT file system#FAT16|16-bit File Allocation Table]]<br />(with 16-bit sector entries)
| introduction_date       = 1984-08-14 (PC DOS 3.0)<br />1984-08 (MS-DOS 3.0)
| partition_id            = [[Master Boot Record|MBR]]/[[Extended Boot Record|EBR]]:{{ubli
 | [[#FAT16|FAT16]]:&nbsp;<code>{{abbr|0x|Values in C-notation for hexadecimal numbers}}[[Partition type#PID_04h|04]]</code> e.a.
 | [[Basic data partition|BDP]]: <code>EBD0A0A2-B9E5-4433-87C0-68B6B72699C7</code>
 }}
<!-- needs more refinement as this is version dependent:
| max_volume_size         = 16&nbsp;[[megabyte|MB]] (with 2&nbsp;KB clusters) --><!-- larger volumes should use logical sectored FAT partition IDs or FAT16B partition ID -->
| max_file_size           = 4,294,967,295 bytes (4&nbsp;GB − 1)<!-- Not "limited by volume size" if volumes larger than 4 GB are possible. -->
| file_size_granularity   = 1&nbsp;byte
| max_files_no            = 65,536 for 32&nbsp;KB clusters<!-- 2^16 − 12 (reserved clusters) − 64 (number of 32 KB clusters for directory entries) -->
| max_filename_size       = [[8.3 filename]] with [[OEM character set|OEM]] characters, 255&nbsp;[[UCS-2]] characters<ref group="nb" name="NB_LFN_UNI"/> when using [[Long filename|LFN]]
| max_directory_depth     = 32&nbsp;levels or 66&nbsp;characters (with [[Current Directory Structure|CDS]]), <br />60&nbsp;levels or more (without CDS)
| dates_recorded          = {{ubli
 | Modified date/time, creation date/time (DOS 7.0 and higher only),
 | access date (only available with [[ACCDATE (CONFIG.SYS directive)|ACCDATE]] enabled),<ref name="Microsoft_2006_ACCDATE" />
 | deletion date/time (only with DELWATCH 2<!-- with Novell DOS 7, Caldera OpenDOS 7.01, DR-DOS 7.02 and higher -->)
 }}
| date_range              = [[Epoch of 1980-01-01|1980-01-01]] to [[Year 2100 problem|2099-12-31]] ([[Year 2108 problem|2107-12-31]])
| date_resolution         = {{ubli
 | 2&nbsp;seconds for last modified time,
 | 10&nbsp;ms for creation time,
 | 1&nbsp;day for access date,
 | 2&nbsp;seconds for deletion time
 }}
| attributes              = [[FAT file attributes|Read-only]], [[FAT file attributes|hidden]], [[FAT file attributes|system]], [[FAT file attributes|volume]], [[FAT file attributes|directory]], [[FAT file attributes|archive]]
| file_system_permissions = {{ubli
 | File, directory and volume access rights for [[FAT file access rights|read]], [[FAT file access rights|write]], [[FAT file access rights|execute]], [[FAT file access rights|delete]] only with [[DR-DOS]], [[PalmDOS]], [[Novell DOS]], [[OpenDOS]], [[FlexOS]], [[IBM 4680 OS|4680&nbsp;OS]], [[IBM 4690 OS|4690&nbsp;OS]], [[Concurrent DOS]], [[Multiuser DOS]], [[Datapac System Manager|System Manager]], [[REAL/32]]:{{ubli
  | execute right only with FlexOS, 4680&nbsp;OS, 4690&nbsp;OS;
  | individual file / directory passwords not with FlexOS, 4680&nbsp;OS, 4690&nbsp;OS<!-- at least I could not find any user or programmer's documentation for it so far -->;
  | [[FAT file access rights|world]]/[[FAT file access rights|group]]/[[FAT file access rights|owner]] permission classes only with multiuser security loaded
  }}
 }}
| compression             = Per-volume, [[SuperStor]], [[Stacker (disk compression)|Stacker]], [[DoubleSpace]], [[DriveSpace]]
| encryption              = Per-volume only with [[DR-DOS]]
}}
In 1984, IBM released the [[PC AT]], which required PC&nbsp;DOS&nbsp;3.0 to access its 20&nbsp;MB hard disk.<ref name="IBM_1984_PCDOS30" /><ref name="IBM_1985_Reference" /> Microsoft introduced MS-DOS&nbsp;3.0 in parallel. Cluster addresses were increased to 16-bit, allowing for up to 65,526&nbsp;clusters per volume. However, the maximum possible number of sectors and the maximum [[Disk partitioning|partition]] size of 32&nbsp;MB did not change. Although cluster addresses were 16&nbsp;bits, this format was not what today is commonly understood as '''FAT16'''.
A [[partition type]] <code>[[Partition type#PID_04h|0x04]]</code> indicates this form of FAT16 with less than 65,536&nbsp;sectors (less than 32&nbsp;MB for sector size 512). The benefit of FAT16 was the use of smaller clusters, making disk usage more efficient, particularly for large numbers of files only a few hundred bytes in size.

As MS-DOS&nbsp;3.0 formatted all 16&nbsp;MB-32&nbsp;MB partitions in the FAT16 format, a 20&nbsp;MB hard disk formatted under MS-DOS&nbsp;3.0 was not accessible by MS-DOS&nbsp;2.0.<ref name="Microsoft_69912">{{Cite web |url=http://c-bit.org/kb/69912/EN-US/ |title=Microsoft Knowledge Base article: "MS-DOS Partitioning Summary" |access-date=2018-06-02  |archive-date=2018-06-12  |archive-url=https://web.archive.org/web/20180612143554/http://c-bit.org/kb/69912/EN-US/ |url-status=live }}</ref> MS-DOS&nbsp;3.0 to MS-DOS&nbsp;3.30 could still access FAT12 partitions under 15&nbsp;MB, but required all 16&nbsp;MB-32&nbsp;MB partitions to be FAT16, and so could not access MS-DOS&nbsp;2.0 partitions in this size range. MS-DOS&nbsp;3.31 and higher could access 16&nbsp;MB-32&nbsp;MB FAT12 partitions again.