Apple's ASIF sparse disk format for VMs reverse-engineered by developer
New virtual disk format for macOS Tahoe gets first third-party parser.
Deep Dive
At WWDC 2025, Apple introduced ASIF (Apple Sparse Image Format), a new sparse virtual disk format for macOS 26 Tahoe's Virtualization framework. Similar to VMDK/VHDX, it enables efficient large disk storage. Developer Erik Schamper reverse-engineered the format and documented his process, revealing the file structure (magic 'shdw', big-endian integers) and the format's design for virtual machines.
Key Points
- Apple announced ASIF at WWDC 2025 for macOS 26 Tahoe's Virtualization framework.
- ASIF is a sparse disk format for VMs, storing only used blocks like VMDK/VHDX.
- Developer Erik Schamper reverse-engineered the format, releasing a parser with documented header structure (magic 'shdw', big-endian integers).
Why It Matters
Apple's ASIF format for VMs now has an open parser, enabling cross-platform compatibility and deeper understanding of macOS virtualization.