Your PC's hard drive is packed with your personal data. So when you want to get rid of your system or drive, you should permanently erase your storage device drives before you get rid of them. If your drives are encrypted and you trust the encryption protocol (full disk encryption is pretty safe), all you have to do is delete your encryption keys. If you want to safeguard your privacy further--and prevent data theft down the road--here are a few cheap and simple tools designed to wipe your hard drive, solid-state drive, or USB flash drive thoroughly before you dispose of it. Because different types of drives use different storage methods, you need different tools to deal with each type. Solid-state drives, for instance, behave very differently from ordinary USB flash drives, hybrid hard drives (which combine a flash cache with a magnetic hard disk), or hard disk drives. This reflects the unique way that SSD firmware writes data to the drive: Wear-leveling algorithms, designed to lengthen the SSD's lifespan, cause data to be written across many different areas inside the drive.
Deleting data during everyday use doesn't remove the data from your drive; instead, it merely erases the pointer to that data. To ex­­punge data permanently, you need an app that writes ones and zeros, literally or figuratively, over your existing data. Before attempting to wipe a laptop's drive, be sure to plug in the AC adapter; if your laptop battery dies halfway through a drive wipe, the hard drive is likely to become corrupted and unusable.
For erasing a traditional magnetic hard-disk drive, try Darik's Boot and Nuke (DBAN), a boot disk block-erasure utility that safely wipes data by overwriting every sector of the drive with random data several times before erasing everything. Because DBAN is designed to wipe magnetic hard disks, however, it often fails to fully erase flash memory, such as in a USB flash drive or an SSD. DBAN also may not work properly if your computer contains a hybrid hard-disk drive/SSD.

Well and Truly Erased

If you have a hybrid hard drive or an SSD, download a copy of the Center for Magnetic Recording Research's free Secure Erase utility; this app--which conforms to the Guidelines for Media Sanitization published by the U.S. National Institute of Standards and Technology--executes the Secure Erase command built into the firmware of Serial ATA (SATA) and Parallel ATA (PATA) hard drives, telling the hard drive to overwrite all memory with meaningless data. To use the tool on your hardware, copy HDDerase.exe to a CD or USB flash drive and boot your PC from that device. Type hdderase at the DOS command prompt that appears, and then press Enter. Your hard drive should securely erase itself by overwriting every sector; the process can take several hours to complete.
To reduce the risk that someone might salvage embarrassing data from your USB flash drive, download a free copy of Roadkil's Disk Wipe utility to match your operating system (Roadkil last updated the software in 2009); then run it while you have the USB flash drive plugged into your PC. Choose the appropriate disk from the drop-down menu, specify whether to fill the drive with random data or just wipe the flash drive to turn it into a blank disk, select how many passes you want the program to perform (stick with 3 to be sure), and let the software go to work.
To guarantee your data's privacy, you pretty much have to take a sledgehammer or a blowtorch to your old drive. But if that's not an option, these secure wipe approaches are the next best thing.