THE CHOICE
BETWEEN DDR4
AND DDR5
Alder Lake supports DDR5, the first PC platform
to do so. It also supports DDR4 memory. The
promise of memory speeds of up to 4800MHz
(effective) might sound enticing, but there’s
more to it than raw memory bandwidth. DDR5
uses PMICs (Power Management Integrated
Circuits) on the DIMMs, and as such, it comes
with different requirements.
First, you need to look at the memory
latency along with the speed. Typical DDR5-
4800 memory comes rated with CAS latencies
of 40, and subtimings are also rated at 38–40.
That might be 50 percent more bandwidth
than DDR4-3200 can provide, but the actual
latency is worse. DDR4-3200 CL16 has an
actual latency of 10ns, while DDR5-4800 CL40
has 16.7ns latency. Other factors come into
play, but using Intel’s officially supported
memory speeds of DDR4-3200 or DDR5-4400,
it’s a mixed bag of results. Some applications
and games prefer DDR4, others prefer DDR5.
If it were just performance, we could move
on, but the choice between DDR4 and DDR5
has wide-ranging implications. First, much
like graphics cards, DDR5 is currently sold
out. Hopefully, the supply will improve,
but recommended prices for DDR5 2x16GB
kits range from $280–$350, and prices are
currently heading in the wrong direction. Asimilar capacity DDR4 kit will only set you
back about $75–$100.
There’s also the question of what
motherboard you want to use. If you prefer
high-end ones, you are limited to DDR5
designs. Conversely, if you want a DDR4
motherboard, the highest quality options are
at best classified as midrange solutions. We’re
okay with midrange motherboards in general,
but pairing a top-tier CPU and cooler with a
modest motherboard is a bit odd.
You won’t find any motherboards with
both DDR4 and DDR5 slots. The reason is that
DDR5 has much more stringent signaling
requirements, so it needs more board layers
and the routing of traces needs to be more
precise. Trying to support two memory types
gets in the way, and people willing to pay the
price premium for a DDR5 board likely won’t
want to be restricted to using just two DIMMs.
If you run at stock-supported speeds, also note
that you can only run at DDR5-4800 if your
board has just two physical slots; otherwise,
you’re limited to DDR5-4400.
As if that wasn’t enough, there’s also the
matter of memory gears. Like other recent
processors, Alder Lake can run its memory at
a 1:1 ratio (Gear 1), or it can use a 2:1 ratio (Gear
2). It performs best with Gear 1, but that will
typically only get you up to around DDR4-
4000 or DDR5-4000. Luck of the draw will be
a factor, but DDR4 defaults to Gear 1 all the
way up to the officially supported DDR4-3200,
while DDR5 runs in Gear 2 by default and
requires Gear 2 for speeds above 4000MHz.DDR5 memory is the
new hotness, but in
practice it’s hit and miss.
Games often run better
with DDR4, while media
encoding tends to prefer
DDR5’s raw bandwidth.the empire strikes back
34 MAXIMU MPC FEB 2022