Why does NASA use those really old computers?

Some of those computers are ancient. Why not upgrade to something a little bit more modern? You'd think that they would have the top-of-the-line technology, not old clunky computers that are over 40 years old.

Why does NASA use those really old computers?security

I'm going to add to what scythian1950 said.

First of all, I'm going to assume, as scythian did, that you're talking about seemingly outdated chips on spacecraft, as NASA's got plenty of modern computing power on the ground in its research centers

As scythian mentioned before, spacecraft development is a factor contributing to the age of the chips used. Spacecraft avionics and electronics are developed in parallel with the rest of the spacecraft, so it's not possible for a designer to simply drop in the newest technology right before launch.

Another factor to consider is the development of the chips themselves. Except in a few very rare cases, once a satellite is launched into orbit, it is not possible for anyone to reach the satellite to perform mechanical maintenance on it, so the systems on board must be very robust. For this reason, satellites typically use versions of commercial chips that have been modified to withstand the extreme radiation environments in which spacecraft operate. However, due to the extreme amounts of development and testing required to design rad-hardened chips, the availability of rad-hardened chips tends to lag a few generations behind regular top-of-the-line commercial products.