You can refer to this [Wikipedia writeup][1]

And yes, Hardware Manufacturer can be identified from the first 3 octet aka OUI
![Hardware Manufacturer can be identified from the first 3 octet aka OUI][2]

Sources: Wikipedia

**What is an OUI then?**

An OUI {Organizationally Unique Identifier} consists of a 24-bit number that uniquely identifies a vendor or manufacturer. The 24-bit numbers are purchased and assigned by the IEEE. 

  [1]: https://en.m.wikipedia.org/wiki/MAC_address?wprov=sfla1 "MAC Addresses"
  [2]: https://i.sstatic.net/iO9A9.jpg