What is PC3-12800

[Ikapewpew]

So hi guys i am building new pc right now and i just noticed that the RAM was PC3-12800
Normally i just use DDR3 lets say 1333 but what does PC3-12800 mean?

 

[byza]

PC3-12800 is DDR3 RAM that operates at 1600MHz, PC2-6400 would be DDR2 RAM that operates at 800MHz.

 

[Pinhedd]

So hi guys i am building new pc right now and i just noticed that the RAM was PC3-12800
Normally i just use DDR3 lets say 1333 but what does PC3-12800 mean?

PC3-12800 is a PC DRAM bus specification. All x86 based computers use a 64 bit wide memory channel. When that memory channel is populated with DIMMs that use DDR3-1600 DRAM chips, the bandwidth is 12.8 gigabytes per second.

PC3-12800 <- per bus bandwidth specification (12.8 gigabites bidirectional per second per channel)

DDR3-1600 <- per chip transfer rate specification (1600 megatransfers per second per IO pin)

Many mobile devices use 32 bit data buses. In this case, DDR3-1600 chips would yield PC3-6400.

 

[geofcrr]

But please add this vital extra information. Why is there also PC12800U and what is the difference?
I upgraded my wife's PC the other day, gave it some more memory, only to find that PC12800 was incompatible. Further research showed me that the original memory was PC12800U.
I have probably spent the equivalent of a whole 8 hour day if not more looking for an explanation of this with no success.