I'm not completely sure if this the right place to post this. If not I apologize for that and ask one of the administrators or moderators of the forums to move it to the appropriate place.
The availability of the source code of the first version of Photoshop was done in conjunction with Adobe and Computer History Museum. It's 128,000 lines of code that we can all now go and see the work that was done 23 years ago in 1990 by Thomas Knoll, co-founder of Adobe.
Out of curiosity, every line of code and the very structure of the first version of Photoshop were exclusively the work of Thomas Knoll. It was he who created from scratch and programmed the first version of this software.
Of this code about 75% is Pascal, 15% is Assembler and the remaining, data of different types.
It's not expected to be compiled or used because some proprietary libraries from Apple that were purchased at the time are not available.
The source is available here: Photoshop 1.0.1 Source Code