CREATE TABLE table_203_136 (id DECIMAL, "year" DECIMAL, "ibm model number" TEXT, "name" TEXT, "processor" TEXT, "bus" TEXT, "hd interface" TEXT, "case" TEXT, "notes" TEXT)

which model was the first portable device ?
SELECT "ibm model number" FROM table_203_136 WHERE "case" = 'portable' ORDER BY id LIMIT 1
SELECT "ibm model number" FROM "table_203_136" WHERE "case" = 'portable' ORDER BY "id" NULLS FIRST LIMIT 1