What Is Physical Unit Number (PUN)?

You know how you're sitting there, minding your own business, and someone comes up to you and says, "Hey, I need your PUN."You're like. WTF? What's my what now?? Well, lucky for you, we've got the answer. A Physical Unit Number (PUN) is a device identification number assigned to a Small Computer System Interface (SCSI) device attached to a SCSI controller. In other words: if it's a device that connects to your computer through SCSI, it has a PUN. The thing is that SCSI controllers are pretty rare nowadays. They were popular in the 80s and 90s. Still, since USB came along and replaced them as the standard connection method for peripherals, they've been mainly relegated to industrial uses—like printing presses or home appliances like refrigerators or dishwashers—and some people who like tinkering around with old computers. But if you have one lying around and want to use it on your modern computer? You'll need a PUN! The PUN is like a social security number for your SCSI controller. It helps the controller identify and manage communication with other devices, but it's not all the controller uses to gauge your importance. The SCSI controller can communicate with only one device at a time; therefore, it prioritizes devices using their PUNs. But it also uses its internal system of priorities to decide which device gets what first—and that's where you come in! The more critical you are to your SCSI controller, the higher you will be on its list of priorities. When playing with SCSI devices, using PUN (Prevention of Unnecessary Nonsense) is essential. PUN is a tool that restricts multiple SCSI devices from sending and receiving data simultaneously. Typically, PUN is set using priority IDs ranging from 0-15, where devices with the highest priorities are assigned numbers from 0-7, and devices with the lowest importance are posted from 8-15. If you've got two substantial storage drives on your computer and want them to run simultaneously, they'll need different priorities.