upgrade to 128mb on 1k

My question is when I upgrade to 128mb do I have to re install jjos 3.12 again?

If you mean when you install the RAM, then no you don't need to re-install the OS.
You can swap the RAM out whenever you want as the operating system is stored seperately.

Thank you for your response. very helpful.

Furthermore you do not need to get the official Akai 128 ram modules that may cost up to $150, you can get any 'PC 133 144PIN CL3 SODIMM 256MB' ram module (aftermarket ram must be 256 if you want to get your MPC to read a max of 128).

Just got a samsung recently off ebay for ~8$ shipped, more than worth it.

i just brought the PC 133 144PIN CL3 SODIMM 256MB ram today off ebay. thanks again for your feedback...