CREATE TABLE table_3894 ("Model - Computer name" TEXT, "CPU type" TEXT, "No. of processors" TEXT, "Period of operation" TEXT, "Maximum peak performance  (  Teraflops  ) " TEXT, "Use" TEXT)

Name the total number of model for amd opteron dual-core 2.6ghz
SELECT COUNT("Model - Computer name") FROM table_3894 WHERE "CPU type" = 'AMD Opteron dual-core 2.6GHz'
SELECT COUNT("Model - Computer name") FROM "table_3894" WHERE "CPU type" = 'AMD Opteron dual-core 2.6GHz'