Pascal and Motorola 68000 assembly, 179 files, about 128,000 lines; held by the Computer History Museum
Source withheld. Its licence permits study but not reproduction; the link leads to the original.
Thomas Knoll wrote the first version of this program in 1987, while a PhD student at the University of Michigan, and called it Display. His brother John, who worked at Industrial Light & Magic, convinced him it could be a product and wrote many of its image-processing plug-ins. Adobe licensed it in April 1989 and shipped Photoshop 1.0 in February 1990.
The frame is empty on purpose. The museum's terms allow anyone to download and read the code, but not to post it again, so this placard can only describe it. There are 179 files and about 128,000 lines, roughly three quarters Pascal and most of the rest 68000 assembly, with the MacApp library from Apple left out. Grady Booch, who wrote the essay that accompanied the release, said that opening it felt like Howard Carter breaching the tomb of Tutankhamen, and praised "the consistent naming, the granularity of methods, the almost breathtaking simplicity of the implementations". The current Photoshop runs to more than ten million lines. The 1990 program it grew from is one of the few pieces of commercial software from that era whose insides can be read at all.