Courtesy of the Computer History Museum and Adobe Systems themselves
Adobe Systems Inc. has given the Computer History Museum permission to release the source code of the 1990 version 1.0.1 of Photoshop, free of charge, for non-commercial use.The Computer History Museum website seems to be down under heavy workload (probably because of the crazy headlines saying FREE PHOTOSHOP), but the reality is that Photoshop 1.0.1 isn’t of much use on today’s computers.
Provided that you are actually able to run it, adafruit reports that pretty much all the code is there, excepting the MacApp applications library licensed from Apple.
The zipped folder contains 179 files “comprising about 128,000 lines of mostly uncommented but well-structured code,” according to the report.
The source adds that roughly 75% of the code is in Pascal, and about 15% is in 68000 assembler language. The rest is “data of various sorts.” Users must agree to the terms of the license before downloading Photoshop 1.0.1.