CompTIA A+ Certification All-in-One Exam Guide

dual-channel, but with three or four sticks of RAM instead of two. More
recently, Intel and AMD systems have switched back to dual-channel,
although there’s plenty of systems out there using triple- or quad-channel
memory.
EXAM TIP Be sure you are familiar with single-, dual-, triple-, and quadchannel
memory architectures.
Table 4-3 shows common DDR3 speeds. Note how DDR3 I/O speeds are
quadruple the clock speeds, whereas DDR2 I/O speeds are only double the
clock. This speed increase is due to the increased buffer size, which enables
DDR3 to grab twice as much data every clock cycle as DDR2 can.
Table 4-3 DDR3 Speeds
DDR3L/DDR3U
Memory manufacturers offer a low-voltage version of DDR3, most
commonly labeled DDR3L, that provides substantial cost savings when used
in massive RAM applications. (Think big data centers, like the ones that
power Google.) DDR3L runs at 1.35 volts (V), compared to the 1.5 V or 1.65
V of regular DDR3, providing cost savings up to 15 percent—that adds up
fast! The ultra-low-voltage version of DDR3, DDR3U, runs at a miserly 1.25
V.
Lower voltage means less heat generated. In a server farm or data center,