Apple - How to know whether Mac has SSD or HDD installed

  • Apple Menu -> About This Mac -> System Report
  • Select Storage in the Hardware section
  • Select "Macintosh HD" on top

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Alternatively you can run system_profiler SPSerialATADataType or system_profiler SPStorageDataType in Terminal which more or less gives you the same information

Apple Menu -> About This Mac -> System Report -> Hardware -> SATA/SATA Express

For my MacBook Pro (Early 2015) this showed the Serial-ATA Device Tree, from which I was able to get the model number for my SSD. This related question, How to get serial number from Mac hard disks? might help if you think you have an HDD.