Memory - Upgrading and Repairing PCs - page 416

DDR DIMM Details
The 184-pin DDR DIMMs use a single key notch to indicate voltage, as shown in Figure
6.12 .
Figure 6.12 The 184-pin DDR SDRAM DIMM keying.
DDR DIMMs also use two notches on each side to enable compatibility with both low-
and high-profile latched sockets. Note that the key position is offset with respect to the
center of the DIMM to prevent inserting it backward in the socket. The key notch is po-
sitioned to the left, centered, or to the right of the area between pins 52 and 53. This in-
dicates the I/O voltage for the DDR DIMM and prevents installing the wrong type into a
socket that might damage the DIMM.
DDR2 DIMM Details
The 240-pin DDR2 DIMMs use two notches on each side to enable compatibility with
both low- and high-profile latched sockets. The connector key is offset with respect to the
center of the DIMM to prevent inserting it backward in the socket. The key notch is posi-
tionedinthecenteroftheareabetweenpins64and65onthefront(184/185ontheback),
and there is no voltage keying because all DDR2 DIMMs run on 1.8V.