Archived - Mac OS X 10.4: About Disk Utility's secure erase options

This article has been archived and is no longer updated by Apple.

In Disk Utility in Mac OS X 10.4 Tiger, there are four Security Options you can use if you wish to securely erase a volume:

  • Don't Erase Data
  • Zero Out Data
  • 7-Pass Erase
  • 35-Pass Erase

"Don't Erase Data" option

Erases directory information so that data is no longer accessible. The data itself is left unchanged on the disk until its disk space is required, at which point it is written over. Data is potentially recoverable until then. This option is the quickest, but least secure.

"Zero Out Data" option

Writes zeros over all data on the disk. This option provides good data security in a minimum amount of time.

"7-Pass Erase" option

Writes data over the entire disk seven times. This provides a highly secure erasure of disk data. A 7-Pass erase takes 7 times longer than a Zero Out Data erase.

Advanced information: The 7-Pass Erase option conforms to the DoD 5220.22-M specification. This specification calls for three passes, but Disk Utility performs seven. Visit here for more details on the specification.


Pass

Data written
Inbinary notation
Inhexadecimal notation
1
11110110
0xF6
2
00000000
0x00
3
11111111
0xFF
4
Random
Random
5
00000000
0x00
6
11111111
0xFF
7
Random
Random


"35-Pass Erase" option

Writes data over the entire disk 35 times. This option provides highly effective security against the recovery of data. It requires 35 times more time to perform than the Zero Out option.

Advanced information: The 35-Pass erase option uses the Gutmann algorithm, which means 35 patterns are written to the disk to overwrite data. You can find out more about the Gutmann method here or here. In the chart below, RLL means Run Length Limited, and MFM means Modified Frequency Modulation.

Pass

Data written

Encoding scheme targeted

In binary notation

In hexadecimal notation

1RandomRandom


2RandomRandom


3RandomRandom


4RandomRandom


501010101 01010101 0101010155 55 55(1,7) RLL
MFM
610101010 10101010 10101010AA AA AA(1,7) RLL
MFM
710010010 01001001 0010010092 49 24
(2,7) RLLMFM
801001001 00100100 1001001049 24 92
(2,7) RLLMFM
900100100 10010010 0100100124 92 49
(2,7) RLLMFM
1000000000 00000000 0000000000 00 00(1,7) RLL(2,7) RLL
1100010001 00010001 0001000111 11 11(1,7) RLL

1200100010 00100010 0010001022 22 22(1,7) RLL

1300110011 00110011 0011001133 33 33(1,7) RLL(2,7) RLL
1401000100 01000100 0100010044 44 44(1,7) RLL

1501010101 01010101 0101010155 55 55(1,7) RLL
MFM
1601100110 01100110 0110011066 66 66(1,7) RLL(2,7) RLL
1701110111 01110111 0111011177 77 77(1,7) RLL

1810001000 10001000 1000100088 88 88(1,7) RLL

1910011001 10011001 1001100199 99 99(1,7) RLL(2,7) RLL
2010101010 10101010 10101010AA AA AA(1,7) RLL
MFM
2110111011 10111011 10111011BB BB BB(1,7) RLL

2211001100 11001100 11001100CC CC CC(1,7) RLL(2,7) RLL
2311011101 11011101 11011101DD DD DD(1,7) RLL

2411101110 11101110 11101110EE EE EE(1,7) RLL

2511111111 11111111 11111111FF FF FF(1,7) RLL(2,7) RLL
2610010010 01001001 0010010092 49 24
(2,7) RLLMFM
2701001001 00100100 1001001049 24 92
(2,7) RLLMFM
2800100100 10010010 0100100124 92 49
(2,7) RLLMFM
2901101101 10110110 110110116D B6 DB
(2,7) RLL
3010110110 11011011 01101101B6 DB 6D
(2,7) RLL
3111011011 01101101 10110110DB 6D B6
(2,7) RLL
32RandomRandom


33RandomRandom


34RandomRandom


35RandomRandom


 

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Last Modified: Feb 20, 2012
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  • Last Modified: Feb 20, 2012
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