---
name: "newfs_msdos"
section: "8"
platform: "macos"
package: "msdosfs"
version: "788.100.31"
release: "macOS 26.5"
platforms: ["freebsd", "openbsd", "macos"]
url: "https://new.carta.tech/newfs_msdos"
---

# newfs\_msdos(8)

construct a new MS-DOS (FAT) file system

## NAME

**newfs\_msdos** – construct a new MS-DOS (FAT) file system

## SYNOPSIS

**newfs\_msdos** \[**-N**\] \[**-B** *boot*\] \[**-F** *FAT-type*\] \[**-I** *volid*\] \[**-O** *OEM*\] \[**-S** *sector-size*\] \[**-a** *FAT-size*\] \[**-b** *block-size*\] \[**-c** *cluster-size*\] \[**-e** *dirents*\] \[**-f** *format*\] \[**-h** *heads*\] \[**-i** *info*\] \[**-k** *backup*\] \[**-m** *media*\] \[**-n** *FATs*\] \[**-o** *hidden*\] \[**-r** *reserved*\] \[**-s** *total*\] \[**-u** *track-size*\] \[**-v** *volume-name*\] *special* \[*disktype*\]

## DESCRIPTION

The **newfs\_msdos** utility creates a FAT12, FAT16, or FAT32 file system on device *special*, using [disktab(5)](/disktab/5.md) entry *disktype* to determine geometry, if required.

The options are as follows:

- **-N**

  Don't create a file system: just print out parameters.

- **-B** *boot*

  Get bootstrap from file.

- **-F** *FAT-type*

  FAT type (one of 12, 16, or 32).

- **-I** *volid*

  Volume ID.

- **-O** *OEM*

  OEM string (up to 8 characters).  The default is "BSD  4.4" (with two spaces).

- **-S** *sector-size*

  Number of bytes per sector.  Acceptable values are powers of 2 in the range 128 through 32768.

- **-a** *FAT-size*

  Number of sectors per FAT.

- **-b** *block-size*

  File system block size (bytes per cluster).  This should resolve to an acceptable number of sectors per cluster (see below).

- **-c** *cluster-size*

  Sectors per cluster.  Acceptable values are powers of 2 in the range 1 through 128.

- **-e** *dirents*

  Number of root directory entries (FAT12 and FAT16 only).

- **-f** *format*

  Specify a standard (floppy disk) format.  The eight standard formats are (capacities in kilobytes): 160, 180, 320, 360, 640, 720, 1200, 1232, 1440, 2880.

- **-h** *heads*

  Number of drive heads.

- **-i** *info*

  Location of the file system info sector (FAT32 only). A value of 0xffff signifies no info sector.

- **-k** *backup*

  Location of the backup boot sector (FAT32 only).  A value of 0xffff signifies no backup sector.

- **-m** *media*

  Media descriptor (acceptable range 0xf0 to 0xff).

- **-n** *FATs*

  Number of FATs.  Acceptable values are 1 to 16 inclusive. The default is 2.

- **-o** *hidden*

  Number of hidden sectors.

- **-r** *reserved*

  Number of reserved sectors.

- **-s** *total*

  File system size, in sectors.

- **-u** *track-size*

  Number of sectors per track.

- **-v** *volume-name*

  Volume name (filesystem name), up to 11 characters.  The name should consist of only those characters permitted in regular DOS (8+3) filenames.

## NOTES

FAT file system parameters occupy a "Boot Sector BPB (BIOS Parameter Block)" in the first of the "reserved" sectors which precede the actual file system.  For reference purposes, this structure is presented below.

```
struct bsbpb {
    u_int16_t	bps;		/* [-S] bytes per sector */
    u_int8_t	spc;		/* [-c] sectors per cluster */
    u_int16_t	res;		/* [-r] reserved sectors */
    u_int8_t	nft;		/* [-n] number of FATs */
    u_int16_t	rde;		/* [-e] root directory entries */
    u_int16_t	sec;		/* [-s] total sectors */
    u_int8_t	mid;		/* [-m] media descriptor */
    u_int16_t	spf;		/* [-a] sectors per FAT */
    u_int16_t	spt;		/* [-u] sectors per track */
    u_int16_t	hds;		/* [-h] drive heads */
    u_int32_t	hid;		/* [-o] hidden sectors */
    u_int32_t	bsec;		/* [-s] big total sectors */
};
/* FAT32 extensions */
struct bsxbpb {
    u_int32_t	bspf;		/* [-a] big sectors per FAT */
    u_int16_t	xflg;		/* control flags */
    u_int16_t	vers;		/* file system version */
    u_int32_t	rdcl;		/* root directory start cluster */
    u_int16_t	infs;		/* [-i] file system info sector */
    u_int16_t	bkbs;		/* [-k] backup boot sector */
};
```

## EXAMPLES

```
newfs_msdos /dev/disk0s1
```

Create a file system, using default parameters, on /dev/disk0s1.

```
newfs_msdos -f 1440 -v foo fd0
```

Create a standard 1.44M file system, with volume name "foo", on /dev/fd0.

## SEE ALSO

[fdisk(8)](/fdisk/8.md), [mount(8)](/mount/8.md)

## DIAGNOSTICS

Exit status is 0 on success and 1 on error.

## HISTORY

The **newfs\_msdos** command appeared in FreeBSD 3.0.

## AUTHORS

Robert Nordier ⟨rnordier@FreeBSD.org⟩.