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What Is a BKF File? How to Open Windows NT Backup Archives

A BKF file is a Windows NT Backup archive that starts with the letters TAPE. Jump to your question below, or work through it in order.

26 min read Updated October 2026 Checked against Microsoft, Wikipedia and FileInfo pages and 12 test files

What Is a BKF File? NTBackup archives from Windows XP and older

Short answer

BKF files are backups made by Windows NT Backup, the backup tool in Windows XP and older versions. They pack files and folders into one archive, and the format belongs to Microsoft.

Every real BKF file starts with the four letters TAPE. The letters come from Microsoft Tape Format, the layout NTBackup used for tape drives. Backup Exec and SQL Server use that layout too.

Microsoft's own restore utility is for Windows 7 and Server 2008 R2. It does not list Windows 10 or 11. Check the first letters of your BKF file before you install anything.

BKF files are backup archives from Windows NT Backup, called NTBackup. They pack files and folders into one container, and Windows XP and Server 2003 could create them.

Picture an old office computer that gives you a drive with Backup.bkf on it. The BKF file is 40 GB, and a double-click does nothing. Windows 10 asks which app to use. Most BKF file questions start right there.

Microsoft put NTBackup in Windows from NT 3.51 through Server 2003, says Wikipedia. Windows Vista and Server 2008 replaced it with Backup and Restore and Windows Server Backup. Those two save backups as VHD files.

BKF files use Microsoft Tape Format, or MTF, stored as disk files. Backup Exec and the backup tools in SQL Server use MTF too, according to Wikipedia. So most BKF files come from NTBackup, and some come from other backup programs.

A few other things use the ending, but rarely. The section on other meanings covers them.

BKF file facts at a glance

Property Value
File extension .bkf
Made by NTBackup from Microsoft, which came with Windows XP and Server 2003
FileInfo category Backup Files, developer Microsoft
Layout Microsoft Tape Format (MTF)
Starts with The letters TAPE, which are the bytes 54 41 50 45
Opens in NTBackup on XP and Server 2003, or the Restore Utility on Windows 7 and Server 2008 R2
Replaced by Backup and Restore and Windows Server Backup, which save VHD files

Wrong page? Bink video and BizHawk movie files that end in .bk2 are in the BK2 file guide. Backups that end in .vhd are in the VHD virtual disk guide.

Is Your File a Real BKF File? Read the first four bytes, then check the folder

Read the first four bytes of your BKF file. Real NTBackup files start with TAPE. Anything else is not a Microsoft Tape Format backup, even when the name ends in .bkf.

BKF files can reach many gigabytes, so use a tool that reads only the start. Python does that in one line, and hex viewers work too. Replace Backup.bkf with your file name.

Read the first four bytes of a BKF file 
python -c "print(open('Backup.bkf', 'rb').read(4))"
b'TAPE'

The answer b'TAPE' means your BKF file starts like an MTF backup. Any other answer means something else made the file. The table shows the kinds we found.

Kind First letters Usual place Opens in
NTBackup file TAPE Old backup drives and shares NTBackup or a reader
Backup Exec or similar TAPE for MTF files Backup software folders Its own program or a reader
Moto Racer archive Not checked The folder of a game Dragon UnPACKer
SQLite database Not checked The folder of an app A SQLite viewer
A decision chart: read the first four bytes of the file. TAPE means an MTF backup from NTBackup or similar software, and anything else means another kind of file
Two starts, two answers. Only the first four bytes matter.

Three more clues besides the letters

The size FILExt says its NTBackup samples average about 70 MB. BKF files range from small to huge, so size alone proves nothing.
The folder BKF files from NTBackup live in old backup folders, on external drives and on network shares. One inside a game folder is more likely a game archive.
The file command On Linux and Mac, the file command labeled 10 of our 12 test BKF files Windows NTbackup archive. Those BKF files are ours, so the label is a hint only.
Neither start A different start means your .bkf file is not an MTF backup. Check other uses of the BKF ending before you try more apps.

Who Made the BKF File Format? From a tape layout to a Windows backup

Microsoft built NTBackup into Windows from NT 3.51 through Server 2003, then replaced it with VHD backups in Windows Vista and Server 2008. The tape layout inside BKF files is older than Windows.

The layout began as a tape format. Wikipedia says Microsoft Tape Format started as the proprietary format of Maynard Electronics. Microsoft later licensed it as the standard Windows tape format, and the format changed owners many times after that.

Year Owner Note
1982 Maynard Electronics The software was called MaynStream
1989 Archive Corporation Bought Maynard Electronics
1993 Conner Peripherals Bought Archive and renamed the software Backup Exec
1996 Seagate Software Seagate bought Conner
1999 VERITAS Software Bought the Seagate Software unit with Backup Exec
2005 Symantec Bought VERITAS
2015 Veritas Technologies Split off from Symantec, then independent in 2016
2024 Arctera Backup Exec moved to this new company

Wikipedia lists Arcada, Conner and Seagate Software as the first authors of NTBackup, with Microsoft and Veritas as later developers.

What NTBackup could save

Shadow copies From Windows XP, NTBackup used Volume Shadow Copy to save files that were open.
System State It could save System State and Active Directory data, which are Windows settings and directory records.
Encrypted files It supported files protected by the Encrypting File System, NTFS hard links and alternate data streams.
Unreliable drives Wikipedia lists USB and FireWire drives that fail as a cause of damaged BKF files, with CRC errors and Unrecognized Media messages.

Windows XP Home. XP Home does not install NTBackup by default. The NTBackup article says it is on the install disc, so BKF files can come from Home computers too.

What Is Inside a BKF File? Blocks, headers and streams

BKF files are rows of blocks. Every block starts with a 52-byte header, and the first block is the TAPE block. Streams after the header store names and file data.

Microsoft Tape Format was made for tape drives, which read one long stream in order. BKF files keep that design, so readers can walk them from the top, block by block.

A BKF file drawn as a row of blocks: TAPE, SSET, VOLB, DIRB, FILE, FILE, DIRB, FILE and ESET, with a 52-byte header at the start of every block
The nine blocks of our 9,216-byte test file. Large backups repeat the FILE blocks thousands of times.

The block types you will meet

Letters Name What it stores
TAPE Media header The name of the media and the block size. Every BKF file starts here.
SSET Start of a backup set A set number and a set name. BKF files can contain several sets.
VOLB Volume The drive that was saved
DIRB Directory A folder name and its path
FILE File The file name, then a data stream with the content
ESET End of set Closes the backup set

The list above covers the types we wrote and tested. The go-mtf code names more, like CFIL for corrupt files, EOTM for tape ends and SFMB for filemarks. Other BKF files can use them all.

The 52-byte header every block starts with

Every block starts with the same 52 bytes. The layout below comes from the TestDisk and go-mtf code, which agree. The mtftar code reads two of the fields four bytes earlier, so check any reader against a known file.

Offset Size What it stores
0 4 bytes The block type, for example TAPE
4 4 bytes Block attributes
8 2 bytes Offset to the first stream, which is where the data starts
10 1 byte Operating system ID, then one byte for its version
12 8 bytes Size of the data, as shown to users
36 4 bytes Control block ID, which is 0 when unused
48 1 byte String type: 1 for ASCII text and 2 for UTF-16 text
50 2 bytes Header checksum

The checksum is simple. XOR the first 25 two-byte words of the header, and the answer must equal the two bytes at offset 50. It covers the header only, and it does not cover the file data.

The block letters in a BKF file, in the order of our test file 
54 41 50 45   TAPE   media header
53 53 45 54   SSET   start of a backup set
56 4F 4C 42   VOLB   a volume, for example C:
44 49 52 42   DIRB   a folder
46 49 4C 45   FILE   a file and its name
45 53 45 54   ESET   end of the backup set

What Do 12 Test BKF Files Show? Four tools, twelve results and one silent change

We wrote 12 small BKF files ourselves and read them with four tools. Eight read in full and three stopped with errors. In go-mtf, cut-off files and changed bytes raised no error.

NTBackup BKF files are hard to find in public, and old backups contain private data. So we wrote our own files, using the layout from the TestDisk and go-mtf code. Our BKF files were not made by NTBackup. We did not start NTBackup, Backup Exec, the Restore Utility, SysTools BKF Viewer or Freeviewer BKF Viewer. We did not read the Microsoft specification itself.

12 test files written
4 tools tried on them
8 read in full by go-mtf
1 changed byte that no tool flagged

The 12 BKF files we wrote

File What it tests Bytes
01 normal Three files in two folders, names stored as UTF-16 9,216
02 ASCII strings The same three files, names stored as ASCII 9,216
03 empty set A backup set with no files 4,096
04 two sets The normal backup twice in one file 17,408
05 Unicode names Hindi and Japanese folder and file names 8,192
06 one big file One file of 1 MB 1,054,720
07 cut short Cut off in the middle of a file 6,716
08 bad checksum A wrong header checksum in the TAPE block 9,216
09 wrong letters TAPF at the start instead of TAPE 9,216
10 zeros first 512 zero bytes before the TAPE block 9,728
11 no end The ESET block removed 8,192
12 one byte changed One data byte of hello.txt changed 9,216

The normal file has nine blocks of 1,024 bytes. Hello.txt has 12 bytes, notes.txt has 18 and empty.txt has none. Four tools read them: libmagic 5.45 (the Linux file command), ffprobe 6.1.1 from FFmpeg, go-mtf (a Go library for MTF) and mtftar (which converts MTF data to a TAR stream).

How four tools read the 12 BKF files

File go-mtf mtftar
01 normal 3 files 3 files
02 ASCII 3 files Garbled names
03 empty set 0 files, no error 0 files
04 two sets 6 files 6 files
05 Unicode 2 files, names ok 2 files, names ok
06 big file 1 file, hash right 1 file
07 cut short 2 files, no error 2 files, odd note
08 bad checksum Error: checksum 3 files anyway
09 TAPF Error: checksum Nothing
10 zeros Error: checksum Error: out of order
11 no end 3 files, no error 3 files
12 byte changed 3 files, 1 hash differs 3 files

The file command printed Windows NTbackup archive for 10 of the files, including the one with the bad checksum. It printed data for the two that do not start with TAPE. FFmpeg failed on all 12 files with the message Invalid data found when processing input. That is correct, because a backup is not media. Extraction through mtftar and tar gave the right content for the normal, 1 MB and changed files. The changed byte came through as well.

What the 12 results say about BKF files

Four letters decide The file command called BKF files NTbackup archives when they started with TAPE, and called them data when they did not. It even accepted the BKF file with the bad checksum.
Cuts stay quiet The cut-short file listed two files and no error in go-mtf. The third file was missing. An error-free ending proves nothing about copies.
Changed bytes stay quiet We changed one byte of data. Every tool read the changed BKF file without complaint, and only the output hash showed the change. Our files had no checksum stream, so nothing could catch it.
Names need the right type Hindi and Japanese names read correctly when the BKF file used UTF-16 text. The ASCII-text file gave garbled names in mtftar, which does not read the string type.

Read the results with care. These are small files that follow the layout in open-source code. Backups from NTBackup are bigger, may use compression and may include checksum streams. The results show how tools behave, not how common any case is.

Repeat the check on your own file

The damage section has a short Python script that reads the first block of BKF files. Point it at a copy and it prints the media name and whether the header checksum matches.

What Does Our Expert Say About BKF Files? A note from Neeraj Singh on trusting a backup

Read the first four bytes of your BKF file before you look for software. Then restore a few files from copies and open them. Only a restore proves the backup.

Neeraj Singh

Expert insight

“Most BKF file trouble starts with the wrong app, not broken files. I read the first four bytes before I install anything. MTF backups start with the letters TAPE. In our test, changing one byte inside a file raised no error in any tool, and a cut-off copy still ended without errors. An error-free listing does not prove the data is good. Restore a few files from a copy and open them before you trust the backup.”

Neeraj Singh Manager, Tech Support & Operations 19+ years fixing Windows and system errors

What an error-free listing does not prove

Listings show names and sizes. They show that headers were readable, and nothing more. In our 12-file study, one tool listed a cut-off backup without an error, and another listed files despite a bad header checksum.

Picture a box of folders with an index on top. The index can be right while a page inside is missing. Opening files is the only real test.

Test on a copy. Make a copy of the BKF file, restore three or four files from the copy and open them. If those open, the backup is likely good. If they do not, you found out before you needed the backup.

How Do You Open a BKF File? NTBackup, the Restore Utility or a reader

Open BKF files with NTBackup on Windows XP or Server 2003, or with the Restore Utility on Windows 7 or Server 2008 R2. On newer Windows, use virtual machines or BKF readers.

Windows 10 and 11 have no built-in app for BKF files, so a double-click shows the Open with box. Your choice depends on the Windows version you can reach. Check the first four bytes first, because only TAPE files fit these tools.

Open BKF files with the Windows NT Backup Restore Utility

  1. Confirm the BKF file starts with TAPE.
  2. Read Microsoft's page for the restore utility. It says the utility only restores backups made on Windows XP and Server 2003. It is not meant to stay installed.
  3. The page names Windows 7 and Windows Server 2008 R2 as the systems it supports. A Winhelponline guide reports that Microsoft removed the download, so you may need an old copy.
  4. Start the utility from the Accessories and System Tools folders on the Start menu, as Microsoft describes. Select your BKF file and the files you want.
  5. Restore to a new folder. We did not start the utility, so follow its own screens.
  6. Remove the utility when you finish, as Microsoft advises.

Tape backups need more. Microsoft says the utility leaves out Removable Storage Manager. Restoring from a tape drive therefore needs an older system like Windows XP or Server 2003.

Open BKF files on Windows 10 and 11

Microsoft's page does not list Windows 10 or 11. Two routes remain. The first is a virtual machine with Windows 7 inside it. The second is a reader that does not need NTBackup.

  1. Install virtual machine software and create a Windows 7 machine, or ask someone who has one.
  2. Copy the BKF file into the machine and install the Restore Utility there.
  3. Restore the files to a shared folder, then copy them to your own computer.
  4. Delete the virtual machine when you are done, or keep it for the next old backup.

The Winhelponline guide also describes copying ntbackup.exe and three DLL files from an older Windows into one folder. We did not test that. It moves system files between Windows copies, so a virtual machine is the safer route.

Read BKF files on Linux and Mac

mtftar is free software that reads MTF files and writes a TAR stream. We tested it on our 12 files. The first command lists the names, and the second extracts the files into the current folder.

List and extract a BKF file with mtftar 
mtftar -l < Backup.bkf
mkdir restored && cd restored
mtftar < ../Backup.bkf | tar xvf -

The drive letter becomes a folder, so files from C: land in a folder named C: inside restored. The extraction gave the right content for our normal, 1 MB and changed files. It does not understand ACL streams, so expect to lose permission settings.

Apps that open BKF files

NTBackup XP and 2003 The original program. It opens and restores its own BKF files.
Restore Utility Windows 7 Microsoft's restore-only version for Windows 7 and Server 2008 R2.
mtftar Linux and Mac Free software that converts MTF data to a TAR stream.
go-mtf Developers A free Go library that reads MTF files. We used it to test.
SysTools BKF Viewer Free preview Scans a BKF file and shows what is inside. Saving files needs the paid version.
Dragon UnPACKer Game archives Extracts the Moto Racer kind of BKF file.

Free tools for BKF files

These four links open outside pages: two viewers, Microsoft's description and the format guide.

SysTools BKF Viewer

Scan and preview BKF files

Free preview
Open the SysTools page

Freeviewer BKF Viewer

Preview BKF and ZIP files on Windows

Free preview
Open Freeviewer

Restore Utility page

Microsoft's description of the utility

Microsoft page
Open the Microsoft page

MTF format guide

Programs that use the layout

Wikipedia page
Open the format guide

SysTools says its viewer has Quick, Deep and Range Based scan modes. It adds that Deep Scan applies to Windows NT, Veritas and Symantec BKF files. It also says the free version previews files and the paid version saves them. We did not test it.

Freeviewer's page lists the same three scan modes. It says the free version previews BKF and ZIP files and the Pro version saves them. It needs the .NET Framework 4.0 and lists Windows 7 to 11. We did not test it either.

Why Will a BKF File Not Open? Five causes, and only one of them is the file

When a BKF file will not open, check the Windows version, the first letters, the program that made it, the reader and the file. Only the last check blames the BKF file.

Most failures are mismatches between the BKF file and the app. The backup is fine, and the app does not fit it. Work through five checks before you look for another copy. The red check is the one where the BKF file itself is wrong.

Your Windows has no BKF reader Windows 10 and 11 do not include NTBackup. Microsoft's restore utility page lists Windows 7 and Server 2008 R2. See how to open BKF files on newer systems.
The file is not an MTF backup Read the first four bytes. Anything other than TAPE means game archives, databases or other kinds of file. See what else .bkf can mean.
Another program made it Backup Exec and SQL Server use the same layout with their own rules. Microsoft says Windows and SQL Server backups can share media but are not interoperable. Try the program that made the file first.
The reader rejects the backup A Microsoft Answers thread shows an HP Recovery Manager backup.bkf that NTBackup refused with the message that it contains unrecognized data. That is one user report, and we did not repeat it.
The file is damaged or cut short A copy that stopped early or a drive that failed breaks the file in every app. See how to check for damage.
A decision chart: if a BKF file will not open, check the Windows version, the first letters, the program that made it, the reader and the file
Five symptoms and the first fix for every one. Only check 5 means the file is damaged.

A five-step check

  1. Show file extensions and confirm the name ends in .bkf and not in .bkf.exe or .bkf.zip.
  2. Read the first four bytes. If they are not TAPE, stop and read the list of rarer BKF kinds.
  3. Copy the BKF file to a second drive and work on the copy.
  4. Try the Restore Utility, virtual machines with Windows 7 or readers like mtftar.
  5. If all of them stop, use the header check. A bad header or a short file means you need another copy of the backup.

Test with a second reader. Readers disagree. Our 12 test files showed one tool stopping at a bad checksum while another listed the files anyway. A BKF file that fails in one app may open in another.

How Do You Check a BKF File for Damage? Three checks, and what they prove

A header check proves the start of a BKF file. A listing proves the structure up to the last readable block. Only restoring files proves the data.

Damage hides in three places: the header, the middle and the end. Every check below looks at one of them. We tested all three on our 12 test BKF files, and the results show what a check can and cannot catch.

Damage we caused What the tools did
Wrong letters at the start (TAPF) The file command said data. go-mtf stopped with a checksum error. mtftar listed nothing.
Wrong header checksum go-mtf stopped with an error. mtftar and the file command did not notice.
512 zero bytes before TAPE The file command said data. go-mtf stopped with an error. mtftar printed an out of order message.
File cut in the middle go-mtf and mtftar listed the first two files. Neither reported that the third was missing.
End-of-set block removed All three files read without an error.
One data byte changed No error anywhere. Only a hash of the output showed the change.

Check one: the header

The first block has a checksum. Save the script as check_bkf.py. It reads the checksum and compares it. It also prints the media name and the block size. We tested it on our 12 files, and it matched the results above. It checks the first block only.

Check the header of a BKF file with Python 
import struct, sys
data = open(sys.argv[1], "rb").read(4096)
if data[:4] != b"TAPE":
    print("First four bytes are", data[:4], "- not an MTF backup")
    sys.exit()
check = 0
for i in range(0, 50, 2):
    check ^= data[i] | (data[i + 1] << 8)
stored = struct.unpack_from("<H", data, 50)[0]
size, pos = struct.unpack_from("<HH", data, 68)
name = data[pos:pos + size].decode("utf-16-le" if data[48] == 2 else "ascii", "replace")
print("Media name:", name.rstrip(chr(0)))
print("Block size:", struct.unpack_from("<H", data, 84)[0])
print("Header checksum:", "ok" if check == stored else "does not match")
The answer for our normal test file 
python check_bkf.py Backup.bkf
Media name: Test Media
Block size: 1024
Header checksum: ok

Check two: the listing

Use a reader to list the files, for example mtftar -l < Backup.bkf. Compare the count and the last names with what you expect. Lists that stop early point to cut-off copies. Complete lists only prove the headers.

Check three: restore and open

  1. Copy the BKF file and work on the copy.
  2. Restore three or four files, including the newest and the biggest.
  3. Open them. Documents should open and pictures should show.
  4. If you have the original size or a hash of the backup, compare it with your copy.

Our test BKF files had no checksum stream, so nothing could catch the changed byte. Backups from NTBackup may include checksum streams. We could not test that on files from NTBackup.

Why BKF files get damaged

Unreliable drives Wikipedia lists failing USB and FireWire drives as a cause of CRC errors and Unrecognized Media messages.
Copies that stopped early A copy cut short ends in the middle of a file, like our test BKF file 07. Check the size against the original.
Repair tools Several vendors sell BKF repair software. Their pages are marketing, and we did not test any. Try restoring from copies first.
Age Old media loses data over time. We had no old media to test, so we make no claim about how long a backup lasts.

How Do You Extract or Convert a BKF File? Restore the files, then zip them

Restore or extract the files from BKF files, then zip or copy them. BKF files are backups, so the files inside are what you want.

Think of BKF files as boxes with files in them, not as documents. Opening the box gives you the files. Moving files from one box type to another takes two steps: open, then pack again.

You want Route Status
Your files back Restore with NTBackup or the Restore Utility Not tested here
Files on Linux or Mac Extract with mtftar and tar Tested on our files
One ZIP file Restore or extract first, then zip the folder Needs the first step
A VHD file Not a conversion. Windows Server Backup saves VHD backups itself. Different job
A safe BKF file Copy it to two drives Always
Two paths from a BKF file: the Restore Utility on Windows 7 restores a folder of files, and mtftar on Linux or Mac extracts them, and a zip tool then makes a ZIP file
Open the backup first. A ZIP file comes after the files are out.

Extract the files, then make a ZIP file

  1. Restore the files with the Restore Utility, or extract them with mtftar.
  2. Check that a few of them open.
  3. Select the restored folder and zip it with the zip tool on your computer.
  4. Keep the BKF file until the ZIP file is checked.

The ZIP archive guide explains the output format.

Why VHD is not a conversion target

Windows Vista and later save backups as VHD files, a virtual disk format. VHD backups copy disks. BKF files list files and folders with their data. The layouts differ, and we found no tool that converts one into the other. The VHD guide shows how VHD files work.

Be careful with upload sites. BKF files can contain private documents and old passwords. Do not upload it to a site that promises online conversion. Restore the files on your own computer.

Is It Safe To Open a BKF File? The file is data, and the risk is what you restore

BKF files are data, not programs. The risk is in what you restore from them: old files, old settings and any malware that was on the computer back then.

We read our 12 files and saw only text and test data. Backups from NTBackup may include programs, scripts and old settings. We did not scan any, so we make no claim about malware.

A safety check before you open it

  1. Show file extensions. A name like Backup.bkf.exe is a program, so read the EXE program file guide and do not open it.
  2. Check the source. A BKF file from your own old computer is expected. A BKF file in a message you did not expect needs care.
  3. Read the first four bytes. That step is safe, because nothing starts.
  4. Restore into a new empty folder, never over your working files.
  5. Scan the restored folder with your security software before you open anything.
  6. Skip System State unless you must have it. Wikipedia says NTBackup could save it, and it stores Windows settings that do not belong on another computer.

Safe to read, careful to restore. Reading four bytes is safe. Restoring is where old files return, so do it in a new folder and scan the result.

How Does a BKF File Differ From BAK, VHD and ZIP? Similar jobs, different layouts

BKF files are old Windows backups, BAK files are common backups, VHD files are Windows Vista and later backups and ZIP files are ordinary archives. They look alike and need different tools.

Several backup endings are easy to mix up. The table sorts them by what they are and by the letters they start with. Mix them up and you search for the wrong app.

Ending What it is First letters
.bkf NTBackup archive in Microsoft Tape Format, from Windows XP and older TAPE
.bak A common backup ending. SQL Server backups also use Microsoft Tape Format. Not checked, no sample
.vhd A virtual disk. Windows Vista and later save backups in it. Not checked, no sample
.zip A compressed archive of files PK

Microsoft says all media used for SQL Server backup and restore use MTF. BAK files from SQL Server therefore follow the same layout as BKF files. The two are not interchangeable, because Microsoft says SQL Server cannot back up Windows data.

SQL Server saves its live databases as MDF files, covered in the MDF database file guide. A backup of one is a different file.

Wrong page? A backup that ends in .vbk comes from Veeam, and the VBK backup file guide covers it. A raw copy of a disk is covered in the disk image file guide.

What Else Does the BKF Ending Mean? A game archive, a database and a few more

Other things use the BKF file ending too. The best known is the Moto Racer game archive. Databases and files from other backup programs also appear.

If your BKF file does not start with TAPE, it may be none of the main kinds. Three sites list other meanings, and the table shows what they say.

Meaning What it is Where it comes from
Moto Racer game archive An archive used by the PC game Moto Racer, and possibly other games The game folder. Dragon UnPACKer extracts it.
SQLite database A small database file used by apps. FILExt puts it at about 2 percent of the BKF files it saw. An app folder. The file contains the text SQLite format 3.
Veritas or Symantec backup Backup Exec files in MTF, which SysTools says its viewer scans Backup software folders
No fixed format FILExt says about 8 percent of its BKF samples had no consistent format Unknown

The file-extensions.org list names the Windows backup and the Moto Racer archive. The FILExt page gives the shares: about 90 percent NTBackup archives, 2 percent SQLite and 8 percent other. It also lists TAPE, Media and Backup as common words inside the NTBackup files. Its common file name is Backup.bkf.

We found no public sample of the game archive or the database kind, so we say nothing about their bytes. Both sites are directories, and neither one explains how it counted.

What Is the BKF File Format Made Of? The specification facts we could check

A BKF file is an MTF backup: a row of blocks with 52-byte headers, starting with TAPE. The checksum covers the headers only, and the file data may have no checksum at all.

Item What we could check
Maker NTBackup from Microsoft. Wikipedia names Arcada, Conner and Seagate Software as the first authors.
Layout Microsoft Tape Format (MTF), also used by Backup Exec and the backup tools in SQL Server
Signature TAPE, which is 54 41 50 45, at the start of the first block
Block header 52 bytes, the same for every block type
Header checksum A 16-bit XOR of the first 25 words of the header, stored at offset 50
Text in headers ASCII or UTF-16, set by the string type byte at offset 48
Block types TAPE, SSET, VOLB, DIRB, FILE, CFIL, ESPB, ESET, EOTM and SFMB in the go-mtf code
Compression The go-mtf code names Stac LZS (MTF_LZS221) as the compression type
Replaced by VHD-based backups in Windows Vista and Server 2008, according to Wikipedia
Media type None that we could confirm, so we list none

About the file signature

The first four bytes are the best test. FILExt lists TAPE among the words found inside NTBackup files, and our tools agreed. We did not find a media type for BKF files that we could confirm.

What we left out

We did not read the Microsoft Tape Format specification, which another project cites as Version 1.00a. The layout above comes from the TestDisk and go-mtf code, which agree. go-mtf's own notes differ from its code, so we trusted the code.

We did not use NTBackup, Backup Exec, the Restore Utility, 7-Zip, SysTools BKF Viewer or Freeviewer BKF Viewer. All 12 test files are ours, and none came from NTBackup. So we say nothing about files from NTBackup beyond what Microsoft, Wikipedia, FileInfo and the other pages state.

We also found no source for the file size limits. Some repair vendors say enterprise BKF files of about 20 GB are common, but those pages sell software, so we use none of their numbers.

Sources checked

For the format, Microsoft's utility page, the Wikipedia entry on NTBackup, the Microsoft Tape Format entry and the Backup Exec entry. For SQL Server, the Microsoft documentation on backup media.

For the endings, FileInfo's BKF entry. For user reports, the Winhelponline restore guide and the Microsoft Answers thread. Every test count came from our own tests in October 2026.

Frequently Asked Questions About BKF Files

What is a BKF file?

A BKF file is a backup archive made by Windows NT Backup, the backup tool in Windows XP and older versions. It stores files and folders in Microsoft Tape Format and starts with the letters TAPE. A few other things use the ending, like a Moto Racer game archive.

How do I open a BKF file?

First read the first four bytes of the BKF file. If they spell TAPE, open it with NTBackup on Windows XP or with the Restore Utility on Windows 7 or Server 2008 R2. On newer systems, use virtual machines or BKF readers.

What program opens a BKF file?

NTBackup opens it on Windows XP and Server 2003. Microsoft's Restore Utility opens it on Windows 7 and Server 2008 R2. Free readers like mtftar work on Linux and Mac, and two viewers, SysTools BKF Viewer and Freeviewer BKF Viewer, preview files for free.

Can Windows 10 or 11 open a BKF file?

Not by itself. Microsoft's restore utility page lists Windows 7 and Server 2008 R2 only. A virtual machine with Windows 7 is the usual way, and a BKF reader is another.

How do I know a file is a real BKF file?

Read its first four bytes. An NTBackup file starts with the letters TAPE, which are the bytes 54 41 50 45. Any other start means a different kind of file, like databases or game archives.

How do I check whether my BKF file is damaged?

Check the header, then the listing, then restore a few files from copies. In our test, cut-off copies and changed bytes raised no error in readers. Only opening restored files proves the backup is good.

Can I convert a BKF file to ZIP?

Extract the files first, with the Restore Utility or mtftar, then zip the folder. A BKF file is a backup, so the files inside are what the ZIP file needs. Keep the BKF file until you have checked the ZIP file.

Can I open a BKF file on Linux or Mac?

Yes, with mtftar. It lists the names and writes a TAR stream that the tar command extracts. We tested it on 12 small files we wrote, and it gave the right content for the files we checked.

Is a BKF file safe to open?

A BKF file is data, not a program. Reading its first four bytes is safe. Restore into a new folder and scan the result, because the files inside may be old or unsafe. Check that the name does not end in .exe.

What is the difference between BKF and VHD?

A BKF file lists files and folders with their data and comes from NTBackup. A VHD file is a virtual disk, and Windows Vista and later use it for backups. We found no tool that converts one into the other, so restore files from the BKF file.

What does "backup file contains unrecognized data" mean?

It is a message from NTBackup. A Microsoft Answers thread shows it for an HP Recovery Manager backup.bkf. It can mean the file came from another program or is damaged, so check the first four bytes and try a second reader.

Can I open a BKF file for free?

Yes. The Restore Utility is free from Microsoft, though a guide reports the download was removed. mtftar is free software. SysTools and Freeviewer say their viewers preview files for free and charge to save them. We did not test either one.

Still Stuck With a BKF File? Eight routes out, depending on what went wrong

Your BKF file will not open

Start with the five checks. The Windows version and the first four bytes explain most cases.

You need the files out

Go to the extract steps. Restore first, then zip or copy.

Is your backup a virtual disk that ends in .vhd? The guide to VHD files covers Windows Vista and later backups.

Do you need an archive you can open anywhere? The guide to ZIP files shows how to open one.

Is it a Bink video or BizHawk movie that ends in .bk2? The guide to BK2 files separates the two.

Is it a Veeam backup that ends in .vbk? The guide to VBK files explains it.

Not sure the file is a BKF file at all? Compare its first bytes with the format reference, then see what 12 test BKF files show.

Is it a file type you do not know? Browse the file extension resource library, or send it to us on the submit a file type page.