Datasheet

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Chapter 1
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Personal Computer System Components
Let’s try another. What do you need for a motherboard that features a 333MHz FSB
(actual clock is 166MHz)? Well, just using the 8:1 rule mentioned earlier, you might be on
the lookout for a PC2667 module. However, note that sometimes the numbers have to be
played with a bit to come up with the industry’s marketing terms. You’ll have an easier time
finding PC2700 modules that are designed specifically for a motherboard like yours, with
an FSB of 333MHz. The label isn’t always technically accurate, but round numbers sell bet-
ter, perhaps. The important concept here is that if you find PC2700 modules and PC2667
modules, there’s absolutely no difference; they both have a 2667MBps throughput rate. Go
for the best deal; just make sure the memory manufacturer is reputable.
DDR2 SDRAM
Think of the 2 in DDR2 as yet another multiplier of 2 in the SDRAM technology, using
a lower peak voltage to keep power consumption down (1.8V vs. the 2.5V of DDR). Still
double-pumping, DDR2, like DDR, uses both sweeps of the clock signal for data transfer.
Internally, DDR2 further splits each clock pulse in two, doubling the number of operations
it can perform per FSB clock cycle. Through enhancements in the electrical interface and
buffers, as well as through adding off-chip drivers, DDR2 nominally produces four times
the throughput that SDR is capable of producing.
Continuing the DDR example, DDR2, using a 100MHz actual clock, transfers data in
four operations per cycle (effective 400MHz FSB) and still 8 bytes per operation, for a total
of 3200MBps. Just like DDR, DDR2 names its chips based on the perceived frequency. In
this case, you would be using DDR2-400 chips. DDR2 carries on the effective-FSB frequency
method for naming modules but cannot simply call them PC3200 modules because those
already exist in the DDR world. DDR2 calls these modules PC2-3200 (note the dash to keep
the numeric components separate).
As another example, it should make sense that PC2-5300 modules are populated with
DDR2-667 chips. Recall that you might have to play with the numbers a bit. If you multiply
the well-known FSB speed of 667MHz by 8 to figure out what modules you need, you might
go searching for PC2-5333 modules. You might find someone advertising such modules, but
most compatible modules will be labeled PC2-5300 for the same marketability mentioned
earlier. They both support 5333MBps of throughput.
DDR3 SDRAM
The next generation of memory devices was designed to roughly double the performance
of DDR2 products. Based on the functionality and characteristics of DDR2’s proposed
successor, most informed consumers and some members of the industry surely assumed
the forthcoming name would be DDR4. This was not to be, however, and DDR3 was
born. This naming convention proved that the 2 in DDR2 was not meant to be a multi-
plier, but instead a revision mark of sorts. Well, if DDR2 was the second version of DDR,
then DDR3 is the third. DDR3 is a memory type that was designed to be twice as fast as
the DDR2 memory that operates with the same FSB speed. Just as DDR2 was required to
lower power consumption to make up for higher frequencies, DDR3 must do the same. In
fact, the peak voltage for DDR3 is only 1.5V.
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