What to download

Which iso should I download

QNX 6.1 ISO at 442mb or…
QNX 6.2.1 NC ISO image at 237

what’s the difference?

You should download QNX 6.2.1 NC ISO because it is the latest release for non-commercial use. After 6.1 QSSL dropped off mkifs and support of some non-x86 CPUs from non-commercial version. That non-x86 CPU support probably should never be included in NC, but if you want to learn the process of creating bootable images then you can play a bit with 6.1. Be aware, 6.2.1 supports wider range of hardware, Photon and ATA drives works a bit faster and some (big part of) software won’t run on 6.1, without recompilling at least.