Windows 10
Undderstanding CPUs
In the summer of 2017, two
security vulnerabilities were
discovered, which went
public in January 2018, and
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fabric of the micro-
architecture, built right into
whole families of processors,
including every Intel one
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nightmare for the chip
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exploit speculative
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works on data it hasn’t been
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as part of the speculative
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getting executed, leading to
cache data being open to be
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first Intel patches proved
troublesome, causing crashesand, ironically, damage that
the vulnerabilities hadn’t
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reports of huge performance
losses with patches have
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depending on the task, of a
percentage point or three,
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Intel’s 9th Generation chips
have such modifications, as
will AMD’s forthcoming Zen
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DUHLPPXQHWR0HOWGRZQ technical frighteningly quickly. Intel has
its SmartCache feature, which enables
unused cores to share their L2 cache.
Another technique is worth a mention
here: pre-fetching. This is where data
that is expected to be needed is copied
into the cache before it has been
requested. Clever stuff. Unfortunately, it
recently came unstuck, which required
changes to the microarchitecture (see
‘Ghosts in the machine’ below).
Applications that run in tight circles hit
the cache a lot, and a bigger one is a
relatively easy way to squeeze more
performance out of a design.
Memory controllers now live on the
processor die, which makes sense, as
the two are closely tied together. You
can play around getting faster modules
to work, assuming motherboard
support. Some games appreciate the
extra. But when extensive testing puts
the gains in the order of one percent,
you can spend your money elsewhere
to better effect. However, it is worth
getting the fastest officially supported
memory speed, and look for a low CL
(CAS latency, a measure of internal
latency in accessing specific memory
locations; lower is better) if you want to
squeeze out some extra. Unless you
plan to overclock the bus, faster is
generally a waste.Changing channels
What about channels? This is old tech.
Memory started struggling to supply
enough data way back in the 1960s.
These days, memory is so much faster
that much of the benefit has faded
away unless you are shifting hugeamounts of data. A dual-channel
controller adds another 64-bit bus to
the memory, doubling the bandwidth.
Each channel can be accessed
separately by the processor, and
requires matching modules: configured
speed (modules can run at a number of
speeds, not just the headline one) and
capacity. However, both slots need not
be populated, so you can run a
three-DIMM dual-channel system if you
put them in the right slots.
Intel’s Coffee Lake and AMD’s Zen+
both offer dual-channel memory.
Triple-channel is found in a couple of
Intel’s older i7s, while quad-channel
appears on Threadripper and
Skylake-X. High memory bandwidthAMD’s Ryzen came as something of a shock. It was
better than we expected, and Intel had some solid
competition at last.
Intel’s high-end desktop chip, the Skylake-X. If you need those chip-side PCIe lanes, this is what you
want. Or if you really need 18 cores.Ghosts in the machine