Samsung 840 White Paper page 15

Traditional vs. DDR NAND
The advent of DDR NAND was a key breakthrough in increasing NAND speed. Traditional NAND, also known as "Single Data
Rate (SDR)" NAND, was only capable of processing data on "one edge" of its regulatory signal. ONFI 1.0 and pre-Toggle
Samsung and Toshiba NAND belong to this category. The figure below shows a Read operation for illustrative purposes.
In contrast, modern NAND can handle data on "both edges" of its regulatory signal (or strobe, as it is known). This
concept is similar to how DDR RAM works (DDR stands for "Double Data Rate").
Toggle DDR NAND works much the same way as the DDR NAND diagram above. The strobe that is used to coordinate
the NAND operations has rhythmic rises and falls, and Toggle DDR NAND is capable of processing data on both the rise
and fall.
Processing data on "both edges" of the strobe obviously results in significant speed and efficiency gains. The different
generations of Toggle DDR and ONFI NAND are distinguished by how fast the strobe (or clock in the case of Synchronous
ONFI NAND) itself runs (how fast it can complete one cycle).
Toggle NAND vs. ONFI NAND
In the NAND flash industry, there is some variation in implementation depending on manufacturer. Samsung and Toshiba
make Toggle NAND, whereas everyone else makes what is called ONFI NAND.
Each generation of NAND, whether Toggle or ONFI, differs in the speeds it is capable of delivering: ONFI 1.0 and
pre-Toggle NAND from Samsung and Toshiba (both asynchronous) are capable of speeds up to 50MB/s, ONFI 2.x
(synchronous) and Toggle 1.0 NAND (asynchronous) are capable of delivering up to 200MB/s and 133MB/s respectively,
and ONFI 3.0 and Toggle 2.0 (both asynchronous) are capable of delivering up to 400MB/s. Today's newest NAND chips
are either Toggle 2.0 or ONFI 3.x.
Asynchronous
Up to
50MB
RE
Signal
Data
Data IO
Strobe
Data
Data IO
Synchronous
Up to
200MB/s
SDR and
ONFI 1.0
NAND
Asynchronous
Up to
133MB/s
Data
Data Data Data
Asynchronous
ONFI 2.0
NAND
Up to
50MB
Toggle 1.0
NAND
Toggle 2.0
and ONFI 3.0
3.0 NAND