Hardware Reference
In-Depth Information
In Table 1.3, the memory types FPM and EDO are old, obsolete types of
RAM. Fast page mode (FPM) was a nonsynchronous type of RAM that
had its own speed rating independent of the system bus, expressed
in nanoseconds of latency (delay), such as 70 ns. Extended data out
(EDO) was a type of RAM that needed to be refreshed with electricity
less frequently than other RAM of its era, so it offered slightly better
performance than standard RAM.
Different types of SDR and DDR DIMMs and SODIMMs may be similar or
even identical in overall size and shape, and may even have the same number of pins.
(For example, DDR2 and DDR3 DIMMs both have 240 pins.) To ensure that people
don't install the wrong type of RAM, each type of RAM has a uniquely placed notch in
the edge that contains the pins. That notch makes the RAM fi t only in a slot that has a
correspondingly placed spacer. Figure 1.9 compares DDR2 and DDR3 DIMMs; notice the
difference in notch placement.
FIGURE 1.9
DDR2 and DDR3 memory modules
Photo credit: Jérôme BLUM.
EXERCISE 1.4
Determining the Type of RAM Installed
1.
Look in the documentation that came with your computer to see if there is anything
about the RAM specifi cations.
2.
In the documentation, locate the information about installing a RAM upgrade. This will
tell you where to fi nd the RAM on your system.
