Hardware Reference
In-Depth Information
The 240-pin DDR3 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 positioned in the center of the area
between pins 48 and 49 on the front (168/169 on the back), and there is no voltage keying because all
DDR3 DIMMs run on 1.5V.
Determining a Memory Module's Size and Features
Most memory modules are labeled with a sticker indicating the module's type, speed rating, and
manufacturer. If you are attempting to determine whether existing memory can be used in a new
computer, or if you need to replace memory in an existing computer, this information can be essential.
Figure 6.16
compares the markings on a 512MB DDR2 module from Crucial Technology and a 2GB
DDR2 module from Kingston Technology.
Figure 6.16. Markings on a 512MB DDR2 module (top) from Crucial Technology compared to
markings on a 2GB (bottom) DDR2 memory module from Kingston Technology.
However, if you have memory modules that are not labeled, you can still determine the module type,
speed, and capacity if the memory chips on the module are clearly labeled. For example, assume you
have a memory module with chips labeled as follows:
MT46V64M8TG-75
By using an Internet search engine such as Google and entering the number from one of the memory
chips, you can usually find the data sheet for the memory chips. Consider the following example: Say
you have a registered memory module and want to look up the part number for the memory chips
(usually eight or more chips) rather than the buffer chips on the module (usually from one to three,
depending on the module design). In this example, the part number turns out to be a Micron memory
chip that decodes like this:
MT = Micron Technologies (the memory chip maker)
46 = DDR SDRAM
V = 2.5V DC
64M8 = 8 million rows × 8 (equals 64) × 8 banks (often written as 64 Meg × 8)
TG = 66-pin TSOP chip package
