How to Securely Erase a Hard Drive and Reinstall the Operating System
April 27, 2011
When a computer is being prepared for sale or is being given away it becomes necessary to wipe it clean and reinstall the operating system. There are several ways to approach the cleaning operation and they vary depending upon the sensitivity of the data that was stored on the drive. For basic computers that were used for general purposes a quick format during installation may suffice. For computers that contained sensitive information that must be kept secure it becomes necessary to perform a systematic overwrite of every sector on the drive to eliminate the possibility of data recovery.
Generic Operating System Installation
Insert the operating-system installation disc into the optical drive and restart the computer.
Press "Enter" when prompted by the computer to boot from the CD/DVD.
Begin the installation operation by following the prompts on the screen. They vary by operating system, but are typically designed to allow a basic installation by choosing the default answer at each prompt. Refer to the documentation that came with the operating system or to the OS manufacturer's website or the website of the computer manufacturer for particular details on a specific OS.
Click on the "Advanced" option when selecting the hard drive to install the operating system on. Delete the existing partitions on the target hard drive and select the resulting unallocated space for the installation. The operating system will create and format a new partition in the unallocated space.
Continue with the operating system installation.
System Recovery Discs
Insert the manufacturer's system recovery disc into the optical drive. If multiple discs are included in the set, insert disc 1 or the operating system disc.
Restart the computer and press "Enter" when prompted to boot from the CD/DVD drive.
Follow the prompts on the screen for a full system recovery to completely erase and reinstall the operating system and all files on the drive. The prompts vary by operating system, but are typically designed to allow a basic installation by choosing the default answer at each prompt. Refer to the documentation that came with the operating system or to the OS manufacturer's website or the website of the computer manufacturer for particular details on a specific OS.
Continue with the operating system installation.
Secure Erase
Download and install a hard-drive wiping software package (See Resources).
Launch the hard-drive wiping software.
Create a self-booting DOS disk wiping CD. The steps vary slightly by software, but are clearly given in the documentation that comes with each software package and on the manufacturer's website.
Insert the drive-wiping CD into the optical drive of the computer to be erased and restart the computer.
Press "Enter" when prompted to boot from the CD/DVD drive.
Follow the steps on the screen to select the number of times the drive will be overwritten in the process and the type of random information that will be written to the drive. The steps vary slightly by software but are clearly given in the documentation that comes with each software package and on the manufacturer's website.
Begin the drive overwrite sequence and allow it to proceed until it has completed. This may take several hours on some computers depending on the speed of the computer, the speed of the hard drive and the exact method chosen.
Resources:
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Reference and Services 
