The part numbers for 7400 series logic devices often use the following naming convention, though specifics vary between manufacturers.
First, although sometimes omitted, a two or three letter prefix which indicates the manufacturer of the device (e.g. SN for Texas Instruments, DM for National Semiconductor) although these codes are no longer closely associated with a single manufacturer, for example Fairchild Semiconductor manufactures parts with MM and DM prefixes, and none.
A two-figure secondary prefix, of which the two most common are "74", indicating a commercial temperature range device and "54", indicating an extended (military) temperature range
Up to four letters describing the logic subfamily, as listed above (e.g. "LS" or "HCT").
Two or more digits assigned for each device, e.g. 00 for a quad 2-input NAND gate. There are hundreds of different devices in each family. The allocation of device numbers (and, with a few exceptions, the pin-outs) of the original 7400 family was carried across to the later families, and new numbers allocated for new functions, plus some of the competing CD4000 numbers and pin-outs were included over time. There is no pattern to the allocation of these numbers. The function and pin-out of the chip is nearly always the same for the same device number regardless of subfamily manufacturer – exceptions are discussed below.
Additional suffix letters and numbers may be attached to indicate the package type, quality grade, or other information, but this varies widely by manufacturer.
For example SN74ALS245N means this is a device probably made by Texas Instruments (SN), it is a commercial temperature range TTL device (74), it is a member of the "advanced low-power Schottky" family (ALS), and it is a bi-directional eight-bit buffer (245) in a plastic through-hole DIP package (N).