While it most likely refers to the , it could also involve a specific Nintendo game or a split-archive file . 🔬 Clinical Research: CCTG PR21

This was part of the "Widescreen" series released in the early 1980s. It is a highly sought-after item for collectors of retro Nintendo gear. 📂 File Management: .R21 Archive Parts

If you are looking at a file named with an extension like .r21 , it is likely part of a .

The most prominent "PR21" is a conducted by the Canadian Cancer Trials Group (CCTG).