IEEE Spectrum May, 2017 - 10

DATA
BYTE

Read latency in microseconds of optane drive versus
solid-state drive when stressed by write demands:

Intel executive vice president William
Holt in the same video.
Whether 3D XPoint, the mystery
technology inside Optane, can live up
to this promise is likely to depend on
the performance it delivers as well as
Intel's ability to scale up manufacturing
using new materials and build out the
right market. The 375-gigabyte Optane
drive on offer now costs US $1,520, about
three times the price of an equivalent
solid-state drive.
This first product will enable data centers to do more with a smaller number
of servers, says James Myers, who works
on nonvolatile memory architecture at
Intel. Myers gives an example of servers running a MySQL database, which,
among other things, apps use to store
instant messages. An equivalent flash
drive can perform 1,400 such transactions per second; the Optane drive can
perform over 16,000.
The Optane drive was announced with
bombast, but the company is coy about
the technology behind it. Myers says
"3D" refers to the fact that the memory
cells are stacked; "XPoint" alludes to the
way the memory elements are arranged.
While flash memory elements must be
read and written in groups, XPoint elements-situated at the crossing point of
interconnects-can be addressed individually. Myers says that this architecture,
and something inherent to the storage
materials themselves, makes 3D XPoint
faster than flash memory.
Intel, which initially developed
3D XPoint in conjunction with Micron,
won't say what the technology really
is, but this doesn't seem to bother
researchers or analysts. "Everyone
seems to think it's phase-change memory," says semiconductor analyst Jim
Handy. "I don't care." What matters to

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him-and, Intel hopes, its customers-is
the performance.
The complexity of today's memory hierarchy-a combination that often includes
magnetic disks and flash for storage and
DRAM and static RAM for memory-is a
necessary evil. Each technology has its
own strengths, so they must be combined.
Data are shuttled around from speedy but
expensive SRAM caches-which are close
to the processor and embedded within it-
to slower, less expensive (but still pricey)
DRAM. Finally, data are stored in slow but
reliable flash or hard-disk drives, or both.
Even if it's not possible to do it all in one
memory technology, using only one for
working memory close to the processor
and one for longer-term storage would
help simplify things. Intel says that XPoint
memory could provide a speedier alternative to flash memory and magnetic hard
disks. The company has also suggested
it could supplement or supplant DRAM.
"DRAM is unique in its ability to waste
power, so anything you can do to get rid
of it is great," says Handy. For example,
Google is thought to store the index of
the entire Internet on several powerhungry, quick-access DRAM servers.
If the company could switch this over
to 3D XPoint-which Intel claims has
10 times the density of DRAM-Google
could use fewer servers and thus save
power and money, according to Steven
Swanson, a computer scientist at the
University of California, San Diego.
Intel is providing software that will
enable computers to operate Optane as
memory as opposed to storage, but it will
be slow. Optane drive latencies max out
at 7 or 8 microseconds-way faster than
flash, which takes hundreds of microseconds, but not touching DRAM's low
hundreds of nanoseconds. The Optane
drives are fettered by the interface they

SPECTRUM.IEEE.ORG

use: They connect to the storage interface, not the memory interface.
In the short term, Intel's drives are not
likely to replace any existing memory
technologies but will instead supplement them, says Swanson, who built a
research drive based on the company's
3D XPoint technology in 2011. Swanson
expects the path to memory and storage
simplification to be complex because
computing systems will have to be redesigned to route data in new ways.
Swanson and Handy believe Intel
started with storage to help smooth
out some of the risk in launching a new
memory technology. Making Optane
a memory requires new circuit board
designs and cooperation from programmers. To get those, Intel needs to show
that there is a market for 3D XPoint and
demonstrate its reliability. Intel says that
a product using a memory interface will
be out in 2018. Even using the interface,
3DXPoint still won't be quite as fast as
DRAM, but Intel promises that it will be
denser and less expensive.
The success of this new memory, then,
will hinge on data centers taking it up in a
less than ideal initial form while the company works on scaling up production.
Even though the flaws in today's memory and storage hierarchy are universally
acknowledged, trying to change it is a risky
move. "Almost all memory companies
have one or two potential competitors to
this technology, and they're all waiting to
see what happens before they jump into
[a] big investment," says Swanson.
Memory enthusiasts disagree about
whether a true universal memory is even
physically possible. It is perhaps most
useful as a goal to guide the computer
industry forward. "The concept of the
universal memory is attractive because
the idea is to simplify," says Wei Lu, a
computer scientist at the University of
Michigan and chief scientist at Crossbar,
a resistive RAM startup company. "We
have a big-data problem, and today's
computers are fundamentally not good
at this." -katherine bourzac

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