5 2 , ▁developed ▁in ▁ 1 9 7 8 , ▁operated ▁at ▁ 7 0 0 ▁k IP S . ▁ ▁The ▁second ▁sub series , ▁released ▁in ▁ 1 9 7 7 – 1 9 7 8 , ▁included ▁the ▁models ▁ 1 0 1 5 , ▁ 1 0 2 5 , ▁ 1 0 3 5 , ▁ 1 0 4 5 , ▁ 1 0 5 5 ▁and ▁ 1 0 6 0 , ▁analog ous ▁to ▁System / 3 7 0 ▁and ▁operated ▁at ▁ 3 3 ▁k IP S — 1 . 0 5 0 ▁M IP S . ▁ES ▁ 1 0 6 0 ▁had ▁up ▁to ▁ 8 M ▁RAM . ▁ ▁The ▁third ▁sub series , ▁released ▁in ▁ 1 9 8 4 , ▁were ▁analog ous ▁to ▁System / 3 7 0 ▁with ▁some ▁original ▁enh anc ements , ▁and ▁included ▁ 1 0 1 6 , ▁ 1 0 2 6 , ▁ 1 0 3 6 , ▁ 1 0 4 6 ▁and ▁ 1 0 6 6 . ▁ES ▁ 1 0 6 6 ▁had ▁up ▁to ▁ 1 6 M ▁RAM ▁and ▁operated ▁at ▁ 5 . 5 ▁M IP S . ▁The ▁fourth ▁sub series ▁had ▁no ▁direct ▁IBM ▁anal ogs ▁and ▁included ▁ 1 1 3 0 , ▁ 1 1 8 1 ▁and ▁ 1 2 2 0 . ▁The ▁last ▁machine ▁in ▁the ▁series , ▁ES ▁ 1 2 2 0 , ▁released ▁in