These instances are grid graphs with rectangular holes. They come from a VLSI application (see JMRW94 ).
They were introduced in KM98 . More information can be found among others in UdAR99 and PD00 .
Here is an image of alue7080 PS DjVu with solution made by E. Uchoa .
This is a picture of diw0495 with solution.
The files can be found in the download section.
The column DC classifies the difficulty of the instance.
The letter after class gives an impression how long it takes to solve the problem using state-of-the-art soft- and hardware. secounds means less than a minute (this includes instances which can be solved in fractions of a second). minutes means less than an hour. hours is less than a day and days is less than a week. weeks mean it takes really a long time to solve this instance. ? means the instance is not solved or the time is not known.
If the number in the Opt column is written in italics the optimum is not known. The number given is the best know upper bound.