Refurbish Computer: Removing Data from Hard Drives

Guide to Digital Data Removal


Removing Data from Computer Hard Drives



How data is stored on the disk


A hard disk is a form of magnetic media used for storing data in computers. Although hard disks can be physically removed, they are not considered a portable form of data storage. The stored data can be erased and the disk re-used. That is what must be accomplished to “wipe the disk clean” for re-utilization.


Hard disks consist of platters or layers that can have data stored on both sides. These layers are divided into tracks, or circular bands, that are subdivided into pie-shaped areas called sectors. In a common default setting, each of these sectors can store up to 512 bytes of data.


When a computer user creates a document or an object and saves it to disk, the information is stored in a sector on the hard disk and an address is created so that it can be located for future use. The file name is a shortcut to that document or object. The delete function removes this shortcut, but not the data.


The delete function is a convenient form of data removal for the computer owner’s everyday needs. Deleting a file from a personal computer is like pulling outdated encyclopedias from the library shelf, storing them in the basement and deleting the reference from the physical and/or digital catalog. The library user can no longer see the old encyclopedias on the shelf or the references indicating where to find them, but they still exist and can be retrieved with a little effort. Deleting the file name and sending the object to the recycle bin (and emptying the bin,) does not remove the data from the disk. It removes only the shortcut. Until the disk is erased, the deleted file is still recoverable with software tools designed for that purpose.


 How to remove stored data from hard disks


Secure removal of all data from a disk is called disk wiping, data destruction, data erasure or data dumping. Disk wiping applies to all kinds of digital storage devices from large disk arrays in servers to individual CDs and flash disks. The disk wiping process overwrites the entire hard disk with data (in the form of zeroes and/or ones) and then the disk is reformatted. The process may be repeated more than once to ensure that all stored information is unrecoverable. 


The U.S. Department of Defense (DOD) standard specifies three iterations (or six passes) to overwrite the hard disk. Each iteration consists of a pass that writes ones over the disk surface and a second pass that write zeroes.


This process could prove very time-consuming, depending on the size of the hard disk. One user reported a time of 12 hours to complete one pass of a 13 GB disk. Software applications have been developed to facilitate the process. Some of these are commercial applications, some are shareware or free. 


The center should select a software tool or tools and specify a standard process for data removal. There are many products that perform these tasks. Some perform the task in a manner that meets the rigorous DOD standard, so there will be no possibility of recovery of data.


One affordable tool for nonprofit organizations


One excellent option for nonprofit AT centers is Blancco. The software conforms to the DOD standard and can produce a written report showing the hard disk serial number and degree of successful wiping. This information may be provided to the donor for assurance that no confidential or proprietary information remained on the disk.

Blancco also supports a donation program to make disk-erasure and reporting tools available to organizations that directly serve youth training, computer refurbishing, and related nonprofit activities. These donations are offered through TechSoup Stock for organizations that meet the following requirements:1

ü       Donated product will be distributed only to qualifying organizations, not individuals.

ü       This donation is available only to U.S. nonprofits with 501(c)(3) designation, U.S. public libraries with 501(c)(3) designation or an FSCS ID, U.S. educational institutions such as all schools, colleges, universities, and vocational schools, and Canadian charitable organizations with a Confirmation of Registration Letter from the Canada Revenue Agency.

ü       To be eligible, an organization must have an annual operating budget of less than $5 million USD.

ü       Each qualifying NPO may request up to 500 licenses (for all products combined) per year within a fiscal year — July 1 to June 30.

ü       Organizations that advocate, support, or practice discrimination based on age, ethnicity, gender, national origin, disability, race, size, religion, sexual orientation, or socioeconomic background are not eligible to participate in this program. Organizations must be willing and able to attest that they do not discriminate on any of these grounds in order to receive donations.

ü       Blancco products may not be transferred or resold.


Wiping the hard disks


Hard disks may be wiped one at a time, or it may be possible to wipe multiple disks simultaneously. Computers for Schools, Inc. in Chico, California, uses a KVM switch box to wipe eight disks at a time, using one monitor, keyboard and mouse.


To wipe the disk, load the disk-wiping software package and follow the manufacturer instructions for the disk erasure software.


When the disk has been wiped, run the report, if the software provides such, and retain it in the center’s records. If no report is available, log the date, time and manner of the disk wiping.



1 Nonprofit Eligibility Requirements and Donor Partner Restrictions, Blancco Restrictions, retrieved February 13, 2008, from


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This work is supported under a five-year cooperative agreement # H235V060016 awarded by the U.S. Department of Education, Office of Special Education and Rehabilitative Services, and is administered by the Pass It On Center of the Georgia Department of Labor – Tools for Life.  However, the contents of this publication do not necessarily represent the policy or opinions of the Department of Education, or the Georgia Department of Labor, and you should not assume endorsements of this document by the Federal government or the Georgia Department of Labor.








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Title: Refurbish Computer: Removing Data from Hard Drives
Module: Program Operations
Author: Trish Redmon
Audience: Implementer
Sub Title:
Organization Source: Pass It On Center
Last Reviewed: 10-25-2009 5:31 PM