How 7-Zip Creates Raw Disk Images from Drives

This article explains how 7-Zip interacts with physical storage drives to capture raw disk data, the technical mechanisms it uses to read physical sectors, and the practical limitations of using an archiver for disk imaging. While 7-Zip is primarily designed for file-level compression, it can access raw storage media at the sector level on Windows systems by reading direct hardware device paths under elevated privileges.

Device Namespace Access

7-Zip accesses physical drives by leveraging the Windows Win32 device namespace rather than standard filesystem pathing. To read directly from a storage device, 7-Zip targets paths such as \\.\PhysicalDrive0 (for an entire physical disk) or \\.\C: (for a specific volume).

Because direct drive addressing bypasses the standard file system, this process requires elevated administrative rights. Without these privileges, the Windows operating system denies low-level read handles to the drive.

Linear Sector Reading

When instructed via the graphical user interface or command-line interface to target a physical drive path, 7-Zip treats the entire physical storage media as a continuous, unformatted stream of binary data.

  1. Sequential Parsing: 7-Zip opens a read-only stream starting at Sector 0 (the Master Boot Record or GUID Partition Table).
  2. Byte-Level Capture: It sequentially reads every sector across the drive, regardless of whether a sector contains active data, deleted files, or empty space.
  3. Partition Invariance: Because it reads the physical drive handle rather than a logical mount point, it captures all partitions, hidden recovery sectors, and unallocated space intact.

Archive Encapsulation vs. Raw .img Output

7-Zip does not natively output a bare, uncompressed .img or .raw disk file directly. Instead, it encapsulates the raw disk stream into an archive container:

  • Container Formats: The stream is usually wrapped into a .7z, .zip, or .tar archive.
  • Compression Modes: Users can apply compression algorithms (such as LZMA or LZMA2) to reduce the image size, or select the "Store" mode (-mx0) to store the sector stream without compression.
  • Extraction to Raw Formats: To obtain a usable .img file from a 7-Zip backup, the user must extract the stored disk stream out of the archive container.

Drive Locking and Volume Consistency

Unlike dedicated backup software that utilizes Microsoft's Volume Shadow Copy Service (VSS), 7-Zip does not automatically freeze the state of active files:

  • Live Data Inconsistencies: Reading an active system drive via \\.\PhysicalDriveX while the OS is actively writing can result in a crash-inconsistent disk image.
  • Volume Locks: In some cases, exclusive locks held by Windows on mounted filesystems may cause read interruptions or failed capture attempts.

Limitations Compared to Forensic Disk Imagers

While 7-Zip can capture raw drive data, it is not a dedicated digital forensics tool:

  • No Bad Sector Skipping: Dedicated tools like ddrescue or FTK Imager handle unreadable sectors by logging errors and zero-filling the target blocks. 7-Zip will typically throw an I/O read error and abort the archiving process if it encounters damaged physical sectors.
  • No Forensic Verification: 7-Zip calculates CRC or SHA hashes for the resulting archive blocks, but it does not generate standardized pre- and post-acquisition forensic hash logs (such as MD5/SHA-256 for the source drive).