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I already tried FORMAT /FS:FAT, diskpart, Disk Management and HP USB Disk Storage Format Tool.

Do I really need to buy a smaller capacity drive? Can't a formatting tool ignore the area beyond 2 GB?

My Asus netbook's BIOS update requires the USB to be formatted as FAT16, and I couldn't get the various Asus BIOS update utilities to work.

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  • 2
    That is an awful restriction on that BIOS flash, yeesh. I'd write them a letter...
    – Shinrai
    Commented Oct 22, 2010 at 15:16
  • 1
    Ken's method works. However the uncooperative Asus bios updater still couldn't read it. I solved my problem by creating a "make MS-DOS bootable" USB stick and using the AFUDOS utility. AFUDOS updated the BIOS in a jiff.
    – William C
    Commented Oct 25, 2010 at 3:52
  • one tip that may solve your problem is dat the filename (the rom) must have the name of youre model. For Example, i have an eeepc 901 so the rom must be renamed to 901.rom
    – user485923
    Commented Aug 19, 2015 at 20:46

5 Answers 5

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Disk Management and DISKPART don't let you delete partitions on removable media. But you can use DISKPART's clean command to nuke it and start over. Here is a series of commands that worked for me:

DISKPART> list disk

  Disk ###  Status      Size     Free     Dyn  Gpt
  --------  ----------  -------  -------  ---  ---
  Disk 0    Online        40 GB      0 B
  Disk 1    Online      7538 MB      0 B

DISKPART> select disk 1

Disk 1 is now the selected disk.

DISKPART> list part

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Primary            500 MB  1024 KB

DISKPART> clean

DiskPart succeeded in cleaning the disk.

DISKPART> create part primary size=500

DiskPart succeeded in creating the specified partition.

DISKPART> active

DiskPart marked the current partition as active.

DISKPART> format fs=fat quick

  100 percent completed

DiskPart successfully formatted the volume.

DISKPART> assign

DiskPart successfully assigned the drive letter or mount point.

This creates a 500MB FAT partition as the only one on the disk. list part is only used to make sure I selected the right disk (and the Size shown was from a previous attempt; yours will say something else closer to the full size).

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  • Okay, this worked because it created me a 500MB usb drive. "FORMAT /FS:FAT" even works on it now, ably reformatting it to 500MB. However, the silly Asus onboard BIOS update program recognizes the drive but can't find the rom file I saved in it. I repeated the whole thing with "create part primary size=1" and then re-FORMAT /FS:FAT-ted it but still the asus update tool can't find my rom file. Do you have any further suggestions?
    – William C
    Commented Oct 22, 2010 at 18:45
  • Is it supposedly listing the contents of the drive, but the list is empty? Use DIR /X to verify that the file has a simple 8.3 file name with the correct extension, all in uppercase. Create some bogus files (like with echo > TEST.ONE), some with the correct extension, and see if they appear.
    – Ken
    Commented Oct 22, 2010 at 21:20
  • No. The bios utility just says, "USB device found. // Reading "1000HE.ROM"... // Can't find "1000HE.ROM" on the USB device!" I tried renaming it to "1000he.rom" or "1000he.ROM" or "1000HE.ROM". Past EEEPC Forum discussions instruct updating the bios in XP first (because there's an Asus BIOS Updater that runs in XP) before installing Windows 7. I might just have to look for someone who has a 1GB usb stick.
    – William C
    Commented Oct 22, 2010 at 22:26
  • I have an ancient 8MB USB key, and it does not have a partition table at all. It's just like a floppy: the boot sector is the first sector, followed by the FAT and root directory. It's easier to read, and maybe what the Asus BIOS is expecting. Try putting the ROM on a floppy, then do a sector copy (like with dd) over the first sectors of the USB, and try that. For more help, open another question; your original one seems to be answered.
    – Ken
    Commented Oct 23, 2010 at 0:42
  • Tip! You can select a partition or volume and issue filesystems alone to see what the file system and allocation unit is set to, or to see what are the default or recommended settings for that partition or volume. You can then issue format recommended quick for instance to let Diskpart decide on those two settings for you. If you want to.
    – Samir
    Commented Jun 4, 2015 at 17:53
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There isn't any way to format a FAT16 partition larger than 4 GB (2 GB under Windows). Use a partitioning tool to repartition the drive (you may need Linux for this).

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Thanks Ken for your suggestion using diskpart. I needed this to do a firmware update to an old Sharp Aquos tv (it would recognize the update, but when it tried to flash it couldn't find it). After converting my 8GB USB to a 512 mb FAT disk, it updated fine.

For anyone who only needs to do this temporarily, here are the steps that worked for me to get it back to its original size. Note that basically I left the size variable off. I also knew I wanted to format it as fat32, but I'm suspicious if you leave off the fs part, it will format it appropriately.

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online          223 GB      0 B
  Disk 1    Online         7657 MB      0 B

DISKPART> select disk 1

Disk 1 is now the selected disk.

DISKPART> list part

  Partition ###  Type              Size     Offset
  -------------  ----------------  -------  -------
  Partition 1    Primary            512 MB  1024 KB

DISKPART> clean

DiskPart succeeded in cleaning the disk.

DISKPART> create part primary

DiskPart succeeded in creating the specified partition.

DISKPART> active

DiskPart marked the current partition as active.

DISKPART> format fs=fat32 quick

  100 percent completed

DiskPart successfully formatted the volume.

DISKPART> assign

DiskPart successfully assigned the drive letter or mount point.

DISKPART>
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  • No, you can't do that. I mean you can't have a 512 MB FAT partition. Your TV must be feeling sick by now if it swallowed a 512 MB portion of FAT. The maximum volume size for FAT16 (16-bit FAT) is 4 GB. That's 64 by 64 KB clusters. Normally the maximum volume size is even smaller. It's usually 2 GB, using smaller clusters. But 4 GB is what you can get away with at most.
    – Samir
    Commented Jun 4, 2015 at 17:10
  • This answer contains conflicting statements. On one hand, if you neglect to specify the partition size with the size option, "the partition continues until there is no more unallocated space in the current region." And in case of a 7657 MB disk, that would exactly end up as one big 7657 MB partition.
    – Samir
    Commented Jun 4, 2015 at 17:30
  • On the other hand, if you attempt to format a partition as FAT, and you failed to specify the partition size to be 4 GB or smaller in the previous step, and that disk in question happens to be larger than 4 GB (7657 MB unallocated, i.e. 8 GB flash drive), you will undoubtedly have a partition larger than 4 GB (as big as the disk itself) and the Virtual Disk Service will be screaming at you: "the volume size is too big... it's too big, it's too big!"
    – Samir
    Commented Jun 4, 2015 at 17:32
  • If I confused you, then I am sorry. I understand you want to be helpful. But you really need to record your steps as you do this. That would make a real working example. You can't come back several days later and play around in Diskpart and record your steps. It will most likely end up being wrong. Wrong commands, wrong output, and no one can follow those steps one by one and get the same result and benefit. They would have to know enough about the commands so they can adopt and adjust them to their own situation. I can try recreate this scenario and expand your answer. Is that OK?
    – Samir
    Commented Jun 4, 2015 at 17:37
  • Just one more short note on "volume". In hope of clearing up some of the confusion about this. A volume is generally a Windows term for a partition, loosely speaking. A more strict definition is that a partition is physical storage unit, while a volume is a logical volume unit. Volumes are handled by Logical Volume Manager (LVM) in Windows and they can contain several physical volumes or partitions rather from more than one physical hard disk drive. I don't know if that was of any help or if it only stirred up the confusion... I will give it a rest for now.
    – Samir
    Commented Jun 4, 2015 at 17:45
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Linux mkdosfs for Windows NT/2K/XP ranks pretty highly on Google when searching for "mkdosfs".

Seems like exactly what you're looking for.

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FAT 16 only supports 2 GB or less.
But you can force format SD card that bigger than 2GB as a 2GB card.

  1. Disk Utility format card by FAT32
  2. e.g. newfs_msdos -F 16 /dev/disk2s1 (path to SD Card device)/(SD Card device number)
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