Dissecting Apple's Sparse Image Format (ASIF)
The author provides a technical walkthrough of reverse-engineering Apple's new Sparse Image Format (ASIF) introduced in macOS Tahoe. The post details the process of creating, mounting, and analyzing the file structure for virtual machine usage.
Why it matters
Technical deep-dives into proprietary file formats help the developer community understand system internals and improve interoperability.
At WWDC 2025, Apple announced macOS 26 Tahoe. One of the new features in macOS Tahoe is a new disk image format: ASIF. Designed for use with virtual machines (its documentation lives under the Virtualization framework ), ASIF takes a lot of inspiration from existing virtual disk formats. Practically, that means it's another sparse virtual disk format, and functions very similar to sparse VMDK, VHDX or QCOW2 files (for the uninitiated, it allow you to store a large disk, or file, in a smaller, "sparse" manner).
The article is a technical tutorial focused on software engineering and reverse engineering.
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