Arista 720XP access switches
Introduced June 4, 2019
In the second part of the model number:
Michael Francini from Arista said something about the packet processor for this switch in an introductory youtube video. https://www.youtube.com/embed/LBY0DfQandQ?rel=0&wmode=transparent. Unfortunately when he talked about the packet processor he could have said X3 or XP -- since they sound very much the same when spoken. As an update to this description [Nov 2021] this is a Trident X3 and that matches the buffer size in the datasheet. An early  version of the datasheet says the packet buffer size is 6 MB, but the current version says 8 MB.
To add the overall picture, the X3 has stacking ports. And ASICs with stacking ports allocate buffer to serve the stack. Sometimes the stack ports can be disabled and their buffer reclaimed. Broadcom and Arista are not explaining this.
The detailed port characteristics of each model are slightly confusing and the best reference is the data sheet. Most tw-pr ports have 30W PoE, but some have 60 W PoE, and this is not reflected in the model number. And most tw-pr mGig ports top at 2.5 Gb/s but some can run at 5 Gb/s.