why do some of my kitchen outlets have 4 wires (2 black and

JustAnswer Customer: why do some of my kitchen outlets have 4 wires (2 black and 2 white) and others have 2 wires.
JustAnswer Customer: (1 black and 1 white).
JustAnswer Customer: My house was built in 1978.
JustAnswer Customer: Does this pose any problems as far as safety in my home.
JustAnswer Customer: My boyfriend is currently puting in new 15A-125V GFCI outlets in the kitchen.
Mike G.: Master Electrician: Hi, I'm Mike and I'll be glad to assist you.
Mike G.: Master Electrician: The 4 wire outlets have a feed pair and a pass through to the next outlet on the circuit.
Mike G.: Master Electrician: The 2 wire are the end of the line.
Mike G.: Master Electrician: Typical wiring - No potential for a problem.
Mike G.: Master Electrician: Mike G.41084.9393847569
JustAnswer Customer: Will the wiring hold a GFCI outlet at the end of the line?
JustAnswer Customer: He has replaced the first 2 outlets (which are the 4 wire ones) he is working on the 3rd outlet which is a 4 wire one .
JustAnswer Customer: He can't get it to work.
JustAnswer Customer: 4th outlet at end of the line is a (2wire).
JustAnswer Customer: He can't get it to work either
Mike G.: Master Electrician: You only need one GFCI on a circuit.
Mike G.: Master Electrician: Install the GFCI in the lead receptacle and it will protect the rest of the circuit.
Mike G.: Master Electrician: If you install more than one on a circuit.
Mike G.: Master Electrician: The wiring in the boxes with 4 wires will need the wires connected to the line terminals only.
Mike G.: Master Electrician: Otherwire the receptacles downsteam will not reset if the power is cut by the first GFCI.
JustAnswer Customer: So this explains why the 3rd outlet has a green light on the GFCI but won't turn my coffee pot on when you plug it in?
Mike G.: Master Electrician: In most kitchens you only need 2 GFCI's for protection of all the receptacles.
Mike G.: Master Electrician: And yes that would explain it.
JustAnswer Customer: Thank you Mike.
JustAnswer Customer: Trying to make the kitchen safe and bring it up to Code.
JustAnswer Customer: Didn't realize it would cause such a problem trying to put it on every outlet.
Mike G.: Master Electrician: You may have one on every outlet but they all need to be wired to the line terminal only when multiples are on the same circuit.