GDSII

GDSII (Graphic Design System II, often shortened to GDS) is an old binary file that stores named drawings, numbered sheets, and shapes so almost every factory tool can read the same disk.

Two stamps of one notched drawing under a single strap. The notch is stored once.

An editor, a partner's editor, a rule checker, and a mask shop can disagree on everything except this stream of records. The file does not know the process. It knows cell names, layer numbers, a datatype, and geometry stored in integer ticks. On disk the name ends in .gds. The header holds a user unit such as 0.001 micrometer per tick, then a list of cells. A small pad cell might be a few hundred bytes. A phone chip can be tens of gigabytes if someone flattened it first.

The cousin built for huge designs is OASIS, which packs repeated shapes more tightly. An older text cousin is CIF. Board houses usually want Gerber, not GDSII, though some shops will take a stream if the layers have been agreed. The file is a letter about geometry. It is not the chip. The process kit says what layer 31 means. The schematic says which shapes ought to be connected. GDSII will store a beautiful, disconnected mess without complaint.

Longer accounts are GDSII in plain language, what is a layout, and OASIS when GDS gets huge.