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C h a p t e r 7 : h a p t e r 7 :
C R R e c y c l i n g e c y c l i n g 143 143

But the truth of the matter is that even though the data can’t be seen on the computer
once it has been formatted, that only means it can’t seen by the operating system. Quick
formatting just writes to a portion of the disk, but most of the old data is still there and is
readily accessible using fairly common recovery tools. Even disks that have been completely
formatted can be partially or completely recovered.
You can safely decommission your old hard drives using several methods. Let’s talk
about the pros and cons of each one.
Deleting
Deleting data is the most common way for a user to remove information from the hard drive.
The problem is that nothing is actually deleted. When a file is deleted, the file system’s pointer
to that file is removed, but that doesn’t remove the file itself. The only way the file will be
completely removed, using this method, is if data overwrites the area where the file resided.
The data remains on the hard drive, as shown in Figure 7-5, and it can be recovered with
the right software.

Overwriting
Software overwriting is a method in which the hard drive is completely written over with
random data three times. The U.S. Dept. of Defense (DoD) actually requires drives to be
written over three times because there may be problems with the following:
• Ineffectiveness of the overwrite procedures PART III
• Equipment failure, such as a misalignment of read/write heads
• Inability to overwrite bad sectors of tracks of data in inter-record gaps

Software overwriting is illustrated in Figure 7-6.

File Allocation Table File Allocation Table
10101 010 00101 10101 010 00101
00111 01 11100 00111 01 11100
00110 1110 0110 00110 1110 0110
1111 0001 0101 11 1111 0001 0101 11
1011 1110 0011 1011 1110 0011
000111 111000 000111 111000
00001111 11110000 00001111 11110000
1010 0011 1010 001 1010 0011 1010 001
0101 0101 1010 0101 0101 0101 1010 0101
101010 0011 10101 101010 0011 10101
10101 01010 11010 10101 01010 11010
110011 110001 001 110011 110001 001

Old data Data “deleted”
but still present

FIGURE 7-5 Deleting a file doesn’t actually remove it from the drive; this simply tells the computer that
that portion of the hard drive is available to be written to.