Hardware Reference
In-Depth Information
The Strata objectives also ask about triple data rate RAM, but there is
no such thing—at least not by that name. The objectives are most likely
referring to DDR3.
Physical Characteristics of RAM
There have been various sizes and shapes of RAM modules in PCs over the years Today,
however, there are two basic physical types:
dual inline memory modules (DIMMs)
, used
in desktop PCs, and
small-outline dual inline memory modules (SODIMMs)
, used in
portable PCs. Both of these consist of small circuit boards with RAM chips mounted on
them and a row of metal tabs (called
pins
) along one edge.
The
dual
in DIMM refers to the fact that the module uses pins on both
sides of the circuit board. If you count the pins (metal tabs) along one
side of a DIMM, you'll count only half the prescribed number of pins. In
contrast, earlier types of RAM,
single inline memory modules (SIMMs),
had visible metal tabs on both sides of the modules. However, those tabs
were wrapped around the bottom of the edge so they were effectively the
same tab on both sides. SIMMs have been obsolete for many years; they
had either 30 or 72 pins and were used in 486 and some early Pentium
motherboards.
Figure 1.7 and Figure 1.8 show a DIMM and a SODIMM, respectively. The RAM
modules slide into sockets on the motherboard, where the pins connect with corresponding
pins in the socket. Table 1.2 and Table 1.3 list the pins for these RAM modules.
FIGURE 1.7
ADIMM
Photo credit: Martyn M aka Martyx.
