What is a SAB file?
SAB stands for Standard ACIS Binary. It is one of the two "part save file" formats that applications built on the 3D ACIS Modeler use to write model data to disk and read it back. The data inside a SAB file is organized exactly like the data in a SAT file, which is why "SAT file" is often used loosely for both.
A SAB file holds the B-rep entities that the application chooses to save: the topology and geometry of bodies, the attributes attached to them and, optionally, the modeling history that lets a model roll back to an earlier state. Every file also starts with a header that records the product that wrote it and the units of the model.
SAB vs. SAT
Because SAB and SAT store the same content, the choice between them is a trade-off between performance and readability.
| Feature | SAT (.sat) | SAB (.sab) |
| Encoding | ASCII text | Binary |
| Human-readable | Yes, can be opened in a text editor | No |
| Write speed | Reference | About twice as fast |
| File size | Reference | About 10% to 20% smaller |
| Data content | B-rep entities, attributes, optional history | Identical to SAT |
| Typical use | Debugging, inspection, exchange | Large models, frequent saves, compact storage |
What is stored in a SAB file?
A SAB file always begins with a header that contains a product ID and the model units, expressed as a conversion factor from millimeters (for example 25.4 for inches or 1000 for meters). ACIS requires applications to set both before saving.
The body of the file lists the saved entities: bodies with their faces, edges and vertices, the underlying curves and surfaces, and the attributes attached to them, such as colors or application-specific data. Saving the history stream is optional. Assemblies are stored in a related format, ASAT or ASAB, rather than in SAB part files.
What Is SAB Used For? Applications and Industry Use Cases
SAB is mainly used as the native file format of applications built on the 3D ACIS Modeler, in fields such as CAD, CAM, CAE and metrology. It is the preferred option when models are large or saved often, since binary files are faster to write and take less disk space than their text equivalent.
For software developers, SAB is also a convenient way to move exact ACIS geometry between applications, tools and test environments without any conversion. When the data has to reach systems that do not use ACIS, it can be translated to another CAD format, or the other way around.
Challenges or Common Pitfalls
Binary files must be written and read in binary mode. On Windows and macOS, opening the output stream in text mode instead of binary mode corrupts the file. Saves also fail if the product ID and units have not been set first, which is a frequent cause of errors in new integrations.
Because a SAB file cannot be inspected in a text editor, problems are harder to diagnose than with SAT. Teams often switch to SAT temporarily when they need to examine the content of a model or share a test case.
Version compatibility also needs attention. When files are exchanged with applications that use an older ACIS release, the writing application should save to a version that the receiving application can read.
How Spatial Helps
We created SAT and SAB as the save formats of the 3D ACIS Modeler, which reads and writes both encodings to standard stream files or other media through dedicated APIs, with or without history. ACIS can read and write any binary layout on any platform, so SAB files can move between operating systems.
For applications that only need to exchange ACIS data, 3D ACIS Exchange is a toolkit dedicated to reading and writing SAT, SAB, ASAT and ASAB files, without the full modeling API. 3D Viz Exchange adds faceting, measurement and querying of B-rep data, as well as a bridge to HOOPS for visualization.
When ACIS data has to work alongside other CAD formats, our 3D InterOp SDK translates models between formats and generates native geometry for ACIS, CGM and Parasolid.