Custom PC - UK (2019-12)

Byandlarge,muchoftheterminology
whendiscussingcontrollersis intuitive.A
fasterprocessor(withmulti-corechipsnow
commonplace)willallowtheSSDto
coordinateitstasksfaster.Likewise,theRAM
is usedtobufferdataasit’smovedbetween
theNAND,processorandhostinterface.
You’lloftenseereferencestoa controller’s
numberofchannels,whichreferstohow
manyNANDflashbankswithwhichthe
controllercancommunicatesimultaneously.
Withmoderncontrollers,theyrelyheavilyon
spreadingtheloadofbothreadandwrite
operationsacrossmultiplechannels,tokeep
upwithdemand,whichis whylower-capacity
driveswithfewerNANDchips/bankshave
lowerperformance.
Wereit notforthelatestcontrollershaving
upwardsofeightchannels,SSDswouldn’tbe
abletodeliveranywhereneartheircurrent
performance–theflashalonecan’tkeepup
withdemand.
That’salsowhyyou’llsee‘Q32’mentioned
a lotwhendiscussingSSDs,asit referstothe
queuedepthofdatareadandwriterequests.

It’sthefactthatmodernSSDscanmanagea

longandcomplexqueueofdatarequests

that’scrucialtothemmaintainingperformance.

NVME,SATAAND

FORMFACTORS

Recently,thebiggestchangeintheSSD

worldistheintroductionofM.2drives.

Thesesmalldrivesslotdirectlyontoyour

motherboardandcanprovideconsiderably

fasterperformancethanSSDsofold.

ThefirstwaveofSSDs(andmanycurrent

drives)werebuiltaroundtheexisting

standardsofharddrives.Theycameinlaptop

harddrive-sized2.5informfactors,and

connectedviaconventionalSATAdataand

powercables.However,thesestandards

heldbackthepotentialofSSDsintwobasic

ways.Thefirstisthatthephysicalformfactor

ofanSSDcanbefarsmallerandmore

versatilethana harddrive.Whysticktoa

2.5inharddriveshapewhenyoucouldhave

a farslimmer,narrowerandlighterdesign?

What’smore,theSATAstandardalso

limitedtheoverallpotentialspeedofa drive.

TheSATA standard tops out at 6Gbps

(typically 550MB/sec), whereas

SSDshave long since been able to

surpass that figure, with modern drives

pushing upwards of 4,000MB/sec.

This led to the development of a new

driveinterface standard called NVMe that,

instead of using a separate drive-specific

connection standard, plumbs straight into

thePCI-E bus of your PC, the maximum

bandwidth of which tops out at 3.94GB/

sec(PCI-E 3) or 7.88GB/sec (PCI-E 4) for

the4x connection used by SSDs. Drives

usingthis new standard can be connected

tothe PCI-E bus with a variety of physical

methods, but the two most common are

M.2drives or PCI-E expansion slot cards.

PCIE 4

Thelatest development in SSD storage is

themove from the longstanding PCI-E 3

standard to PCI-E 4 standard. This doubles

theavailable total bandwidth on the PCI-E

bus,allowing SSDs to break through the

~3,500MB/sec barrier that was starting to

limit performance on the

very fastest drives.

We looked at the Corsair

MP600 in issue 193, where

it delivered impressive

maximum sequential

speeds 5,008MB/sec read

and 4,268MB/sec write.

It’s not quite the massive

leap we saw when moving

from SATA to NVMe,

but it’s still a significant

bump. However, PCI-E 4 is

currently only available on

AMD X570 motherboards.

THEORETICAL

PERFORMANCE

DIFFERENCES

The end result of the move

to PCI-E buses, 3D NAND,

multi-channel controllers

and, of course, the raw

capability of NAND flash

in general, is that we now

have some phenomenally

fast storage. Even the very

earliest SSDs showcased

the massive drop in access

NOR

NAND

BITLINE

BITLINE

WORD

LINE 0

WORD

LINE 1

WORD

LINE 0

GROUND

SELECT

TRANSISTOR

BITLINE

SELECT

TRANSISTOR

WORD

LINE 6

WORD

LINE 1

WORD

LINE 7

WORD

LINE 2

WORD

LINE 3

WORD

LINE 4

WORD

LINE 5

NAND and NOR flash memory are both still used

with each having advantages and disadvantages

FEATURE/ ANALYSIS