askST: How can I delete all personal data from an old laptop?

Reader Sheila Eber wrote to askST: " How can I totally delete all personal data from an old laptop?

"I would like to donate it to a charity organisation but want to be sure that any residual data is totally wiped out after a manual reset."

Tech writer Lisabel Ting answers her query.

When you store files on a regular hard drive (not a solid state drive), the data is accompanied by a virtual "pathway". This acts like a set of instructions that lets your computer know where the information is, and how to access it.

What usually happens when you delete something normally (e.g. by dragging the folder into the Recycle Bin and emptying it), is that you delete these instructions, but not the data itself.


The data still exists, but is now treated as free space, and can be overwritten if new information is copied onto the hard drive.

In order to securely wipe your data, you will have to overwrite your existing data with nonsense "filler" information.

There are a number of free online tools available for doing so, such as File Shredder ( and Eraser (

The more times you overwrite a hard drive in this manner, the more difficult it will be to retrieve your original data. Two or three cycles are usually sufficient.

However, note that it is very difficult to completely remove all data from a laptop or computer's hard drive and, most of the time, residual information can be recovered by forensic data specialists if they are persistent enough.

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