Why is it recommended to not install any PI programs on the same drive as the operating system?

I cannot provide a definitive answer since I was in no way a part of the decision. But I do recall the infamous Nimda virus in the early 2000's. It attacked various Windows services and systems that were on the boot drive, typically the C: drive. I had one client where I recommended Microsoft Exchange, and I was planning on installing on the E: drive. Before I could do it, they had hired a full-time IT person and cut short my contract. The new hire installed Exchange on the C: drive and just a few weeks later, Nimda wiped out their email system.

For those who had been burned by this, it became a standard practice to install your executeable services and systems somewhere other than the boot drive.

Rick_Davin_3.0​ I got an answer from tech support. They confirmed that isolation for security reasons is a reason for the recommendation to have separate drives. The other reason is so that, if the drive gets full from logs, data, etc., then the full drive will not interfere with the operating system or cause the computer to hang.

Rick_Davin_3.0​ I got an answer from tech support. They confirmed that isolation for security reasons is a reason for the recommendation to have separate drives. The other reason is so that, if the drive gets full from logs, data, etc., then the full drive will not interfere with the operating system or cause the computer to hang.