For the interested software developer, or for those who want to experience a bit of nostalgia, Adobe has released a free and legal copy of the source code of Photoshop version 1.0. The code has been released in conjunction with the Computer History Museum who has detailed the software on their website.
The source code consists of about 128,000 lines and is mostly undocumented. Version 1.0 of the software was created by one sole engineer, Thomas Knoll. Version 2 had just two engineers. Around 75 percent of the code is written in Pascal and about 15 percent is in 68000 assembler language.
The code is free for non-commercial use and can be downloaded from the Computer History Museum. Nearly everything is included, save for the MacApp applications library that was licensed from Apple.