Speed Racers
WE KNOW, MEMORY SPEED can be complicated. Speed and
frequency are often treated as interchangeable statistics,
because they are directly tied to each other; R AM, like many other
components, operates at a specific frequency. This frequency
represents the number of times per second an individual
transistor gate can open and close. With memory operating at,
say, 1,000MHz, these transistors can cycle at a fairly nippy 1,000
million times per second.
If you’re the memory-savvy type, though, you might be
more familiar with the MT/s figure than MHz. Shorthand for
megatransfers per second, MT/s was introduced as a metric
for memory speed when DDR (double data rate) was first
produced, because the newer format of memory was able
to process data at twice the speed by registering an additional
data transfer on the rise and fall of the clock. Frustratingly, many
manufacturers chose to ignore this standard, meaning that
current-generation memory quotes frequency figures that are
double their true operating frequency. If you examine memory
speed using system status analysis software, such as CPU-Z,
you’ll find that your 3,000MHz memory is actually running at
around 1,500MHz. MT/s is technically the more accurate figure,
but MHz is more widely used.
Obviously, more speed is better. Commercially available
memor y speeds have been rising steadily over the last few years,
with the current DDR4 standard reaching as high as 4,800MHz
(or MT/s, to be more precise). Higher speeds reduce your real-
world memory latency, and enable the transferral of more data
within a set period of time. This enables superior performance in
rendering functions and other tasks, although not all processors
are affected equally; if you’re rocking an Intel CPU, you’ll find that
increasing your memory speed will have a far smaller impact
than on an AMD processor. For now, then, capacity remains more
important than frequency.
Memory speed does impact another important feature of
your RAM, however. The channel bandwidth of any memory kit
is determined by memory speed; for those not in the know, thebandwidth is the maximum amount of data that can be transferred
between the memory and CPU within a set period of time. This is
calculated by multiplying the transfer speed (in T/s), the system
memory bus (in bits), and the number of channels the memory is
capable of accessing simultaneously. So, for a set of dual-channel
DDR4-3000 memory running with a CPU using a 64-bit bus, the
channel bandwidth would be 3,000,000,000 x 64 x 2, which is
384,000,000,000 bits per second. A gigabyte per second equals to
8 billion bits per second, so we end up with the far more palatable
figure of 48GB/s. This is the absolute maximum data rate that this
system could achieve; attempts to do anything demanding faster
transfers than this would result in memory bottlenecking.
Assuming that you’re not going to meddle too much with your
CPU, that means that data transfer is determined by more than
just memory speed. When choosing what RAM to put in your
system, consider the advantages of a quad-channel kit over
dual-channel (provided your CPU supports it of course—most
mainstream CPUs are resolutely dual-channel). To be fair, dual-
channel memory support represents a good standard for the
average system, but quad-channel support effectively double
your channel bandwidth, so if you’re using your system for tasks
that demand massive data transfers (such as 4K+ video editing, or
large-scale texture production), four can be the golden number.
Channel support is tied to your motherboard, too. Many
high-end boards support quad-channel memory, but if you’re
considering a memory upgrade for a slightly older system, do
bear in mind that your motherboard might only support dual-
channel. Four DIMM slots is no guarantee of quad-channel
support; many four-slot boards have two primary slots (which
logically should be A1 and B1, but are sometimes A1 and A2 or
A2 and B2, depending on the manufacturer), which provide full
dual-channel speeds. This works both ways: Plug in only one
stick of dual-channel memory and you’ll get half the channel
bandwidth. Smaller motherboards, such as the ITX format, have
only two slots with dual-channel support, due to their layout
specifications, even on X299.Consult the mobo
manual if you’re
not sure which
slots to prioritize.best RAM upgrades
26 MAXIMUMPC SEP 2019 maximumpc.com