The System Information app provides detailed specifications and other information about your Mac hardware and software, including your network and external devices. In some versions of OS X, this app is called System Profiler.
Choose Apple menu > About This Mac. This opens an overview of your Mac, including your Mac model, processor, memory, serial number, and version of macOS. To see the greater detail provided by the System Information app, click the System Report button.
To open System Information directly, press and hold the Option key and choose Apple menu > System Information. You can also use Spotlight to find System Information, or open it from the Utilities folder of your Applications folder.
System Information opens to a system report for your Mac:
Select items in the sidebar to see information about each item. For example, the Hardware section shows your Mac serial number, the Memory section shows how much RAM is installed in each internal memory slot, and the Software section shows which startup disk (boot volume) your Mac is using. You can use the Network section and Network Utility to learn more about your network.
To have System Information read your serial number aloud, choose File > Speak Serial Number.
To save a copy of your system report, choose File > Save.
To learn more about System Information, choose Help > System Information Help.