MaximumPC 2002 09

I

n the past year and a half, solid state

drives have come from nowhere to take

their place as the Next Big Thing in

storage, especially in notebooks. The

MacBook Air and the Asus Eee PC and OLPC

XO-1 (One Laptop Per Child) netbooks were

among the first consumer notebooks to

utilize solid state drives. While SSDs are still

most popular in netbooks, they have begun

appearing in more mainstream notebooks

and even high-end desktops.

SSDs have much higher read speeds

than traditional drives, and with no moving

parts, they’re more durable. They’re not

susceptible to magnetic interference or

vibration, and they use less power and run

much more quietly than standard magnetic

hard drives. Best of all, they come in stan-

dard 3.5-inch and 2.5-inch formfactors with

SATA connectors and emulate traditional

drives, so they’re compatible with existing

architecture. Unfortunately, they’re also

orders of magnitude more expensive per

megabyte, thus limiting widespread adop-

tion, at least for now.

Although the fastest solid state drives

use DRAM for storage (with a battery

backup to preserve data), this White Paper

will focus on flash-based SSDs—the variety

most commonly found in consumer gear.

ARCHITECTURE

As the name implies, a solid state drive’s

first point of departure from a standard

hard drive is that it has no moving parts. A

mechanical hard drive uses

a magnetic read/write head

over rapidly spinning platters,

like a super-high-speed record

player, while a solid state

drive writes data to NAND

flash memory, similar to that

used in other flash-based storage, such as

memory cards and USB thumb drives.

While magnetic hard drives are marvels

of modern engineering, solid state drives

are much simpler—they are composed

of just a SATA interface, a controller that

emulates a hard drive and allocates reads/

writes, and a collection of NAND flash

modules that data is stored on. Since NAND

modules don’t need to wait for a drive head

to find the appropriate data sector on a

moving platter to read data, their random-

access times are extremely fast, as are their

read times. And because they’re solid state,

they neatly sidestep many of the failure

points of traditional drives: Vibration, dust,

magnets, and jarring are all potentially

damaging to the read/write head and plat-

ters in a magnetic drive, but do not affect

flash memory.

Flash-based SSDs come in two flavors:

single-level cell (SLC) and multilevel cell

(MLC). SLCs store one bit of data per cell,

while MLCs store two bits per cell. SLCs

are faster, provide less storage, and last

longer. MLCs are cheaper and store more

data, thus achieving better density rates,

but they are susceptible to higher error

rates and slower read/write times. Most

cheap SSDs, especially those used in

netbooks such as the Asus Eee PC, use

MLCs for cost reasons, while performance

SSDs use SLCs.

For an inside look at an SSD, check out

last month’s Autopsy. For more on NAND

flash memory, see the October 2007 White

Paper (http://tinyurl.com/5kke3p).

AS MORE MANUFACTURERS

GET INTO THE SSD GAME,

PRICES CONTINUE TO GO DOWN.

56 |MAMAMAXIMXIMXIMXIMUUUUMMPPPCC| FEB 09 | http://www.maximumpc.com

WHITE PAPER

R&D^

EXAMINING TECHNOLOGY AND PUTTING IT TO USE

They’re faster and more durable than traditional hard drives and use much less

power. Here’s why they’re the future of personal computing —NATHAN EDWARDS

Solid State Drives

WHITE PAPER

Solid State Drives

WHITE PAPER

Single Level vs. Multilevel Cells

HOW IT WORKS

MLC NAND stores four states per memory cell and allows two bits programmed/read per memory cell.

SLC NAND stores two states per memory cell and allows one bit programmed/read per memory cell.

SLC

One bit

per cell

MLC

Two bits

per cell

Number of cells

Number of cells

REFERENCE POINT

REFERENCE POINT

1

1 1 1 0 0 0

0

0 1

Single-level cells store one bit of data per cell; multilevel cells store two bits but are more suscep-

tible to errors.