The HP 26A toner cartridge is a standard cartridge which prints up to 3,100 pages. The HP 26X is a high yield toner cartridge which contains more toner, and prints up to 9,000 pages. The HP 26X will fit in the same slot as the HP 26A. Only difference between the two is that the high yield HP 26X contains more toner powder. Dimensions are the same so installation procedure is the same.