What is the VDI file format?
Files with the .vdi extension contain virtual disk images along with associated metadata. .vdi is the native image format for VirtualBox, Oracle's system virtualization software. A .vdi file functions as a complete hard-disk container - loaded as a virtual drive by the VirtualBox hypervisor on the host machine. .VMDK and .VHD are similar virtual disk formats that VirtualBox can also open and write.
.vdi is the default disk image format used by VirtualBox when creating a new virtual machine. It stores the guest disk contents - partitions, filesystem, and OS data - while VM configuration (name, RAM, network adapters) is kept separately in a .vbox XML file. VirtualBox was first released in 2007 by innotek, a German software company, initially as a proprietary product under the PUEL (Personal Use and Evaluation License). Later that same year innotek released VirtualBox as open-source under the GNU GPL. In 2008 innotek was acquired by Sun Microsystems, and in 2010 Oracle acquired Sun, bringing VirtualBox under Oracle stewardship - where it remains actively developed as Oracle VM VirtualBox. .vdi images can be mounted on the host system using the vboximg-mount command included with VirtualBox, or converted with VBoxManage clonemedium.
.vdi files are organized in four sections:
- A text pre-header containing the human-readable banner
<<< Oracle VM VirtualBox Disk Image >>>. - A binary metadata header (identified by magic signature
0x7F10DABE) holding virtual size, disk type, block count, and UUIDs. - A disk image block allocation map.
- The disk image data blocks (the actual guest-disk content).
.vdi supports both dynamically allocated mode (only used blocks consume host space) and fixed-size mode (full capacity pre-allocated). The format supports AES-XTS 256-bit encryption (since VirtualBox 5.2) and snapshots via differencing child .vdi files. .vdi files run on Windows, Linux, macOS, and FreeBSD - the main platforms for which VirtualBox is available.
Security & safety
RISK: MEDIUMA .vdi is a disk image, not directly executable on the host - but it contains a full guest OS that runs when booted in a VM, so a downloaded .vdi can harbour malware inside the guest. Run untrusted VMs with no shared folders / limited networking, and treat them like any untrusted system. VDIs can also hold sensitive data from the guest (credentials, personal files), so handle/share as confidential. The image files are large; ensure enough disk space before converting/copying.
Format details
in a nutshellPrograms that open VDI files
Windows4 apps
7-Zip
Open-source Browse files inside without booting: open the .vdi as an archive to extract files from the guest filesystem (read-only). 
Oracle VirtualBox
Open-source Create/attach: File -> Tools -> Virtual Media Manager, or add the .vdi as the disk when creating a VM, then start the VM to boot it.
VBoxManage (CLI, bundled)
Open-source Convert/inspect: VBoxManage clonemedium disk in.vdi out.vmdk --format VMDK (or VHD/RAW). 
macOS2 apps
Oracle VirtualBox
Open-source Attach the .vdi to a VM and boot it (Intel Macs / supported Apple-silicon builds). 
Linux3 apps
Oracle VirtualBox
Open-source Attach the .vdi to a VM and boot, or manage it in the Virtual Media Manager.
qemu-img
Open-source Convert/inspect: qemu-img convert -O qcow2 disk.vdi disk.qcow2 (also raw/vmdk/vhdx). Read VDI without VirtualBox.
libguestfs / guestmount
Open-source Mount the guest filesystem to copy files out: guestmount -a disk.vdi -i --ro /mnt. Technical details
deep spec| File header (text) | ASCII banner `<<< Oracle VM VirtualBox Disk Image >>>` at byte offset 0 |
| File header (binary magic) | `0x7F10DABE` little-endian in binary metadata section |
| Disk allocation modes | Dynamic (sparse, grows on write) and fixed-size (fully pre-allocated) |
| Default data block size | 1 MiB (1,048,576 bytes) per block |
| Encryption | AES-XTS 256-bit encryption of disk data, available since VirtualBox 5.2 |
| Snapshot support | Differencing child `.vdi` files chained to a parent image via parent UUID |
| UUID fields | Image UUID and parent UUID embedded in binary header for VirtualBox media registry |
| VM settings storage | Disk image only; VM configuration (RAM, network, etc.) kept in a separate `.vbox` XML file |
| Compaction | `VBoxManage modifymedium --compact` zeroes unused blocks and reclaims host space |
| Format conversion | `VBoxManage clonemedium` or `qemu-img convert` to/from `.vmdk`, `.vhd`, `.qcow2`, raw |
| Host-side mounting | `vboximg-mount` (FUSE) on Linux/macOS; OSFMount on Windows |
| MIME type | `application/octet-stream` |
| Platform support | Windows, Linux, macOS, FreeBSD (wherever VirtualBox runs) |
| Built-in compression | None - block data is not compressed; compaction only reclaims zeroed unused blocks |
| File structure sections | 4 sections: text pre-header, binary metadata header, block allocation map, data blocks |
| Released | VirtualBox 1.0 (2007); format created by innotek, now Oracle |
| Open standard | Yes · royalty-free |
| Specification | www.virtualbox.org |
VDI conversions
Community Q&A
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