| Readers may be familiar with the TI-83 programmable graphing calculator's assembly language functionality (especially those who took high school math classes in the mid-to-late 1990's). The TI-83's only user-writable storage was 32K of RAM (there was a small lithium battery to keep it powered when you changed the AAA's; also some of the RAM was used for system stuff so somewhat less than 32K was actually available for user purposes). You could write hex values in the program text editor, then you could tell the calculator to execute the hex codes as machine code. I understand the previous models, TI-82 and TI-85, were hacked / backdoored to run user-supplied assembly language, so TI responded by including an official entry point and developer documentation for the TI-83. People later wrote loaders which allowed programs to be stored as binary instead of text (using half the space). Some loaders also had the capability to run binary programs by swapping them into the target address rather than copying them (theoretically a third option would be possible, running programs in-place if they weren't written to depend on their load address, but this wasn't a direction the community went in. gcc users may be familiar with -fPIC which produces code which can run from any address, and this flag is necessary when compiling code for shared libraries.) This allowed people to create massive 20K+ applications (an RPG called Joltima comes to mind), that used most of the available RAM. The fact that this loading scheme made static variables permanent was also quite convenient. (And most variables were static; stack-based addressing would be tough because the Z80 only has two index registers, one of which is used -- or perhaps I should say "utterly wasted" -- by the TI-83 OS.) The next generation, the TI-83+, included I think 256K of flash ROM, and a special silver edition was released which contained 2 MB. |