Difference between numbers and letters on RAM

[karineloo71.kl]

What's the difference between an 11-12-A1 and an 11-13-A1 RAM? I want to buy a new one, and thats the only difference between the two.

 

[COLGeek]

See here: https://en.wikipedia.org/wiki/Memory_timings

And here: http://www.tomshardware.com/answers/id-3168684/ram.html

What specific models of memory are you comparing?

 

[Rexper]

Looking at the first example, 11-12-A1:

The first number (11) represents the CAS Latency - CAS Latency in clocks at maximum operating frequency
The second number (12) represents the SPD Revision - JEDEC SPD Revision Encoding and Additions level
The third number (A1) represents the Gerber File and Revision - JEDEC Reference design file used for this design

According to SK Hynix's label info for DDR3.