What Is a Serial Number and What Is It For?

Definition of Serial Number and Why Hardware and Software Often Uses Them

Picture of a Serial Number Location on a Samsung Notebook
Serial Number Location on a Samsung Notebook. © Samsung

A serial number is a unique, identifying number or group of numbers and letters assigned to an individual piece of hardware or software. Other things have serial numbers too, though, including banknotes and other similar documents.

The idea behind serial numbers is to identify a specific item, much like how a fingerprint identifies a specific person. Instead of some names or numbers that specify a whole range of products, a serial number is intended to provide a unique number to one device at a time.

Hardware serial numbers are embedded in the device while software, or virtual serial numbers are sometimes applied to the user who will be using the software. In other words, a serial number used for software programs are tied to the purchaser, not that specific copy of the program.

Note: The term serial number is often shortened to just S/N or SN, especially when the word precedes an actual serial number on something. Serial numbers are also sometimes, but not often, referred to as serial codes.

Serial Numbers Are Unique

It's important to distinguish serial numbers from other identifying codes or numbers. In short, serial numbers are extremely unique.

For example, a model number for a router, might be EA2700 but that's true for every single Linksys EA2700 router; the model numbers are identical while each of their serial numbers are unique to each particular component.

As an example, if Linksys sold 100 EA2700 routers in one day from their website, every one of those devices would have "EA2700" somewhere on them and they would look identical to the naked eye.

However, each device, when first built, had serial numbers printed on most of the components that are not the same as the other bought that day (or any day).

UPC Codes are common as well but are actually not unique like serial numbers. UPC Codes are different than serial numbers because UPC Codes are not unique to each individual piece of hardware or software, as serial numbers are.

The ISSN used on magazines, and ISBN for books, are different as well because they're used for whole issues or periodicals and aren't unique for every instance of the copy.

Hardware Serial Numbers

You've probably seen serial numbers many times before. Nearly every piece of the computer has a serial number including your monitor, keyboard mouse and sometimes even your entire computer system as a whole.

Internal computer components like hard drives, optical drives and motherboards, also contain serial numbers.

Serial numbers are used by hardware manufacturers to track individual items, usually for quality control.

For example, if a piece of hardware is recalled for some reason, customers are usually made aware of which particular devices need service by being provided a range of serial numbers.

Serial numbers are also used in non-tech environments like when keeping inventory of tools borrowed in a lab or shop floor. It's easy to identify which devices need returned or which ones have been misplaced because each of them can be identified by their unique serial number.

Software Serial Numbers

Serial numbers for software programs are usually used to help ensure that the program's installation is only performed one time and only on the purchaser's computer.

Once the serial number is used and registered with the manufacturer, any future attempt to use that same serial number can raise a red flag since no two serial numbers (from the same software) are alike.

If you're planning on reinstalling a software program you've purchased, you'll sometimes need the serial number to do so. See our guide on how to find a serial key if you need to reinstall some software.

Note: Sometimes, you might find that a software program can attempt to make a serial number for you that you can use to activate a program illegally (since the code wasn't legally purchased). These programs are called keygens (key generators) and should be avoided.

A serial number for a piece of software is not usually the same as a product key but they are sometimes used interchangeably.