Why do ICs often have multiples of the same configuration, with different part numbers?

Question

Take the SN54AHC125/SN74AHC125 tri-state quad buffer, for example. Data sheet is here: http://www.ti.com/lit/ds/symlink/sn74ahc125.pdf

Refer to page 7, and you will see this (snippet):

Click here for a larger version

SN74AHC125DGVR, SN74AHC125DGVRE4, and SN74AHC125DGVRG4 (the TVSOP entries; middle of image) have the same properties according to that chart. What's even weirder is that chips with the same properties, from the same manufacturer, might cost different! I looked through the datasheet to see if it had anything to do with packaging, but I still couldn't find anything.

So why do multiple part numbers exist that reference the same part/configuration?

Real example

The reason I actually asked this question is that I'm interested in buying a small-ish quantity of said buffer chip. I want this one, but I also see a seemingly identical chip (with the addition of G4 at the end of the part number) for a few cents cheaper. I thought there must be a reason it's cheaper, but I (obviously) couldn't figure out why.

Answer 1

This may help, from my reading the E4 or G4 designation seems to be based on the RoHS information; E4 and G4 are basically the same but the E values are used for JEDEC marking while the G values are used for TI-Green marking.

As for the pricing I can only speculate that Texas Instruments would prefer to sell one part (the G4 part in this case) over the other options.

Answer 2

The first column in that table is "orderable device", which indicates that different codes won't refer to functional differences, but rather finishing and packaging.

From this document:

SN74LS00D Standard part number
SN74LS00DE4 Pb-Free + NiPdAu part number
SN74LS00DG4 Pb-Free + NiPdAu + ‘green’ mold compound part number

That's also what timrorr refers to. Other differences in ordering codes may refer not just to the device package, but also how parts are delivered.

Here an "R" is appended to the ordering code to indicate "Tape and Reel" packaging instead of "Tube".