Albert Barnes Commentary 1 Samuel 27:8

"And David and his men went up, and made a raid upon the Geshurites, and the Girzites, and the Amalekites; for those [nations] were the inhabitants of the land, who were of old, as thou goest to Shur, even unto the land of Egypt." — 1 Samuel 27:8 (ASV)

The Geshurites bordered the Philistines and lived in the mountainous district that terminates the desert on the northeast (marginal reference). They were a different tribe, or at least a different branch of it, from the Geshurites who lived on the northeast border of Bashan and were Arameans (2 Samuel 15:8). The Gezrites, or Gerzites, may be connected with those who gave their name to Mount Gerizim.