Specifications

52 IBM Power 770 and 780 Technical Overview and Introduction
The POWER7 processor used on the 4-socket processor card also has two memory
controllers, but only one is used. This results in four DIMMs per memory controller, the same
as the processor used on the 2-socket processor card.
Similarly, the processor used on the 4-socket CPU card has two GX++ buses, but only one is
used (Figure 2-11).
Figure 2-11 Processor interconnects on 4-socket processor card
2.3 Memory subsystem
On the Power 770 and Power 780 servers, independently of using two or four Single Chip
Modules (SCMs), each enclosure houses 16 DDR3 DIMM slots. The DIMM cards for the
Power 770 and Power 780 are 96 mm tall, fully buffered, and placed in one of the 16 DIMM
slots on the processor card.
2.3.1 Fully buffered DIMM
Fully buffered DIMM technology is used to increase reliability, speed, and density of
memory subsystems. Conventionally, data lines from the memory controllers have to be
connected to the data lines in every DRAM module. As memory width and access speed
increases, the signal decays at the interface of the bus and the device. This effect traditionally
degrades either the memory access times or memory density. Fully buffered DIMMs
overcome this effect by implementing an advanced buffer between the memory controllers
and the DRAMs with two independent signaling interfaces. This technique decouples the
DRAMs from the bus and memory controller interfaces, allowing efficient signaling between
the buffer and the DRAM.
2.3.2 Memory placement rules
The minimum DDR3 memory capacity for the Power 770 and Power 780 systems is 64 GB of
installed memory.
P7
XYW
A
B
MC0
MC1
GX1
GX0
DIMM 1
DIMM 2
DIMM 3
DIMM 4
GX1 Bus (4 Byte – 2.46Gb/s)
W Y X Buses
8 byte
2.8 Gb/s
B Buses
8 byte
2.464 Gb/s