How to Permanently Erase Data from HDDs and SSDs 🇺🇸

July 25, 2025 · Editor · 3 min read

Original source: Eze Martínez

This video from Eze Martínez covered a lot of ground. Streamed.News selected 6 key moments and summarises them here. Everything below links directly to the timestamp in the original video.

If you plan to sell or dispose of a device, ensure your private data is truly gone. The method varies drastically between traditional hard drives and solid-state drives.

How to Permanently Erase Data from HDDs and SSDs

Permanently deleting data from a traditional hard drive (HDD) requires demagnetizing the surface, physically destroying it, or overwriting it with new data. These methods irreversibly alter magnetic data fields. However, SSD data erasure is more complex. Due to wear-leveling algorithms, SSDs constantly reallocate information. A single overwrite does not guarantee complete erasure. To fully erase an SSD without physical destruction, perform six to seven full overwrite cycles.

"Overwriting your entire SSD doesn't mean it's completely erased; some sectors may remain untouched."

▶ Watch this segment — 9:21

Emptying Recycle Bin Doesn't Delete Files, Just Changes a Bit

Emptying your recycle bin does not delete file data. The operating system only changes a single bit in the file table, flagging that space as available. The original information remains on the disk until new data overwrites it. This efficiency allows data recovery programs to exist. These tools simply revert that bit, changing its value from zero to one, to restore access to the 'deleted' file. Bit-by-bit deletion would be too slow for daily operations.

"The information remains; only a single bit changes. Realize nothing actually gets deleted?"

▶ Watch this segment — 8:36

File Systems Don't Delete Data, Only Mark It Available for Overwriting

Deleting a file does not physically remove it from the disk. Instead, the file system, like Windows' NTFS, manages a logical operation. This system organizes disk blocks and maintains a Master File Table (MFT) index, mapping file locations. Files split and save to available blocks to prevent fragmentation and optimize space. When you delete a file, the file system does not empty its blocks. It simply modifies an 'in use' flag in the MFT, setting it to 'false.' This tells the OS those blocks are available for new data, but original data persists until overwritten.

"When we delete a file, the file system simply sets this flag to false, marking it available for overwriting."

▶ Watch this segment — 6:27

Quantum Mechanics Drives SSD Data Storage

Solid-state drives (SSDs) store data in billions of microscopic NAND Flash cells. Each cell's "floating gate" holds a bit: trapped electrons mean zero, their absence means one. SSDs use quantum mechanics' "tunneling effect" to trap or release these electrons, which sit within a dielectric insulator. An electric field forces electrons across this barrier, sometimes just 70 atoms thick, allowing subatomic data writing and rewriting.

"Trapped electrons mean zero. No electrons mean one. It's that simple."

▶ Watch this segment — 5:12

Hard Drives, CDs Use Magnetism and Light for Data Storage

Before SSDs, storage technologies relied on different physical principles. Hard drives (HDDs) operate via magnetism. A copper coil head creates a magnetic field, polarizing a ferromagnetic material on the spinning platters. An upward pole represents a one, a downward pole represents a zero. Optical media, like CDs and DVDs, use light to read and write information. A laser beam detects microscopic height differences—bumps and valleys—on the disk surface. The system interprets light reflection from these irregularities as the binary sequence that forms the data.

"Down means zero, up means one. That's how it works for all data."

▶ Watch this segment — 4:14

All Files Store as Strings of Zeros and Ones

Digital storage fundamentally converts all information into binary format. To save an image, for example, the computer first decomposes it into pixels. It then translates each pixel's color values, along with other metadata, into a long sequence of zeros and ones. This bit string physically records onto non-volatile storage media, such as a hard drive, SSD, or USB memory. Unlike volatile RAM, which loses data when power is cut, these devices preserve information long-term, keeping the binary sequence intact.