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GDSII is a database format, which in the integrated circuit industry has been the de facto standard for IC layout data exchange for more than two decades. Originally it was developed by Calma for that company's layout design computer system named Graphic Data System. Now the format is owned by Cadence.
It is a binary format for representation of planar geometric shapes, text labels and some other information in hierarchical form. The objects are grouped by numeric attributes assigned to them: "layer number" and optional "datatype" or "texttype" (datatype and texttype is not supported by layout). While basically these attributes were to correspond to the "layers of material" used to manufacture an integrated circuit, very soon their meaning had become more abstract, reflecting the way how the physical layout of a circuit is being designed.
Originally it was designed as a format of data files used to control integrated circuit photomask plotting. Despite its limited set of features and low data density, it was ubiquitously used for transfer IC layout data between design tools from different vendors which operated with proprietary data formats.
GDSII files are considered to be a final output the IC design cycle and are passed to IC foundries for IC fabrication. Originally the GDSII files were produced on tapes. Therefore the final moment of the IC design is known as tapeout.
Currently, many IC design tools (like layout) are beginning to support a new format, OASIS, which may replace GDSII due to higher data density. OASIS is sometimes claimed to be 10 to 50 times more compact than GDSII.
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