Instance

An instance is a stamp that places a named drawing at a chosen spot and facing a chosen way, without photocopying every rectangle inside it.

Pointing at the master is the cheap operation. Copying the ink is the costly one. One inverter cell can appear ten thousand times. Each instance stores a location, a rotation or a mirror, and sometimes a magnification. Change the master and every placement updates. Copy the rectangles by hand and one of them will be missed. Click one small square in a sea of identical squares and the status line names the master, the origin, and an orientation such as R0 or MX. That click did not add another 12 rectangles to the file.

Three stamps of that same L. One is turned. The square stays on the corner that turned with it.

Instances stack. A bit instance sits inside a bank instance, and that bank sits inside the chip. The resulting tree is hierarchy. A row-and-column pack of the same instance is an array. Exploding the stamps into loose shapes is to flatten them. A mask shop may require that explosion, and it hurts if the drawing still needs edits. The instance is a use of a cell, not a second cell. The cell is the named original. Delete the last instance and the cell can remain in the file, unused.

See cells and instances and hierarchy and flattening.