Their function, package and pin arrangement are exactly the same. 74LS244 is a bipolar TTL digital integrated circuit with an operating voltage range of 5V±5%. 74HC244 is an HCMOS digital integrated circuit with an operating voltage range of 2~6V. The former has a large input current up to milliamperes, while the latter has an input current below 1μA and an output level very close to the supply voltage or ground potential. These are not achieved by 74LS244. In addition, the 74LS244 power consumption can reach tens of mW, while the 74HC244 static power consumption is less than 1μW.