Northbridge

In the part "Northbridge", one will find the interface memory DDR. It is the first difference between different the processor from the family 64 bits from AMD. Athlon 64 manage an external data bus of 64 bits, the FX and Opteron of the data buses of 128 Bits. As these processors manage memories ECC, Athlon 64 bits will accept memory ECC on 8 bits of control against 16 bits-ECC for the others. The socket processor is thus different for the 64 and 64 FX.Part JTAG - Debug is related to the difficulty in testing complex electronic circuits. This developed method fine of the Eighties makes it possible to test "outside" the electronic circuit by memorizing the values of entries and exits. It thus is not directly used in the PC.

Hyper transport is the fast bus allowing connection between northbridge and Southbridge. The number of channels is 1 for Athlon 64 and Athlon 64FX. For the opteron, it is of 3 channels. Each channel is able to transfer 3,2 GB/s in each direction (6,4 GB/s on the whole).

All this explains in particular different the socket for the family Athlon 64, Athlon 64: socket 754, advanced mid- 2004 towards the socket 939 which manages Dual Channel

Athlon 64 FX: socket 940 (identical to the opteron), advanced mid- 2004 towards the socket 939 (identical to Athlon64). First Athlon FX51 were thus of Opteron with 2 of the three channels hyper decontaminated transport. Athlon FX53 becomes again Athlon 64 (which it replaces) with a more important mask.