Difference between 74HC/LS/HCT/F series chips.
1, LS is low-power Schottky, HC is high-speed COMS. LS is slightly faster than HC. HCT inputs and outputs are compatible with LS, but with lower power consumption; F is a high-speed Schottky circuit. 
2, LS is TTL level, HC is COMS level.
3, LS input open-circuit high level, HC input is not allowed to open-circuit, hc generally require a pull-down resistor to determine the level of the input is invalid. LS does not have this requirement!
4, LS output pull-down strong pull-up weak, HC pull-up pull-down the same.
5, different operating voltages, LS can only use 5V, and HC is generally 2V to 6V; and HCT's operating voltage is generally 4.5V to 5.5V.
6, different levels, LS is a TTL level, its low and high levels of 0.8 and V2.4, respectively, while the CMOS in the operating voltage of 5V for 0.3V and 3.6V, respectively, so the CMOS can drive the TTL, but the reverse is not possible!
7, the driving ability is different, LS general high level driving ability of 5mA, low level of 20mA; and CMOS high and low power average of 5mA.
8, CMOS devices are poor anti-static ability, prone to bolting problems, so the CMOS input pin can not be directly connected to the power supply.  

74 series integrated circuits can be roughly divided into 6 categories : .
.74×× (standard type); .
.74LS×× (low-power Schottky); . 
.74S×× (Schottky).
.74ALS×× (Advanced Low Power Schottky); . 
.74AS×× (Advanced Schottky); .
.74F×× (high speed).
In recent years there is also a 74 series of high-speed CMOS circuits, which can be divided into 3 categories: .HC for COMS operating level; .
.HCT for TTL operating level, can be used interchangeably with the 74LS series; .HCU for CMOS circuits without buffer stage.
These 9 kinds of 74 series products, as long as the back of the same label, its logic function and pin arrangement is the same. According to different conditions and requirements can be selected from different types of 74 series products, such as the circuit supply voltage of 3V should be selected 74HC series of products series level typical transmission delay ns maximum drive current (-loh/Lol) mA

AHC CMOS 8.5-8/8
AHCT COMS/TTL8.5-8/8 
HC COMS 25-8/8
HCT COMS/TTL 25-8/8 
ACT COMS/TTL10-24/24 
FTTL6.5-15/64
ALS TTL10-15/64LSTTL18-15/24 

Note: The same type of 74 series, 74HC series, 74LS series chips, logic function is the same. 

Refer to the instructions for the 74xx or 74HCxx if you can't find them for the 74LSxx. 

Some of the information contained in several chips, such as 74HC161 information contained in the 74HC160, 74HC161, 74HC162, 74HC163 four chip information. When you can't find information on a particular chip, try checking the information on a neighbouring model.The 74HC is faster than the 4000 series, and the pinout is compatible with the standard 74 series.The benefit of the 4000 series is that some models can operate at +15V.