Serial ATA, planned as a replacement for Parallel ATA, is picking up tempo and is expected to be the dominant physical storage interface within a few years, although there are indications of a few obstacles that could cause delays.
Silicon vendors will be instrumental in providing progressively higher levels of integration and lower costs to ease Serial ATA's acceptance. Hard drives incorporating more highly integrated devices are due late this year or early 2004. Semiconductor companies are prominent voices in a chorus of industry heavyweights supporting the technology.
"There was pretty universal agreement that Parallel ATA was not extendible anymore," said David Jones, vice president and general manager of LSI Logic Corp.'s storage and computing ASICs Division in Fort Collins, Colo. "The decision was to go with a serial electrical interface. There was a need for higher transfer rates."
While Ultra ATA/100 and Ultra ATA/133 parallel interfaces deliver maximum transmission data rates of 100 and 133Mbytes/s, Serial ATA provides rates of 1.5Gbits/s (or a user data rate of 150Mbytes/s). Moreover, the Serial ATA roadmap calls for rates of 3Gbits/s in 2004 and 6Gbits/s in 2007.
Although interface speed is independent of processor speed, the market craves both, said Marc Noblitt, manager of interface planning at Seagate Technology LLC's Longmont, Colo., design center. "As a system gets faster, you have a faster bus, and you want a faster interface with your drive."
Simpler, more compact designs also make Serial ATA technology attractive. Intended as a drop-in solution with existing software and operating systems, Serial ATA's point-to-point architecture allows four or eight ports to be aggregated into a single controller typically located either on the motherboard or as an add-in RAID (redundant array of independent disks) card. In contrast, Parallel ATA supports two parallel ports, each supporting two internal drives.
Serial ATA calls for a longer, thinner cable, in response to OEM efforts to improve airflow and heat dissipation, and allows for the design of smaller boxes. The emerging interface technology also addresses silicon suppliers' concerns over the viability of 5V tolerance for future designs. Additional benefits include lower pin counts and hot-plug capability.
On the riseiSuppli Corp., El Segundo, Calif., forecasts that worldwide shipments of Serial ATA drives will amount to 1.1 million units this year and more than triple, to 3.6 million, in 2004, when it will exceed parallel ATA shipments.
"This year we expect PC makers to integrate the technology but reserve it for the high end," said Dave Reinsel, an analyst at research firm IDC who is based in Hutchinson, Minn. "This will be the value-capture year for Serial ATA deployment, with more massive deployment in 2004."
For PCs, the serial interface offers faster access to large e-mail and Internet files; benefits for laptops include lower power needs and a smaller wire size.
The point-to-point architecture, combined with desktop storage pricing, makes Serial ATA a good candidate for deployment in entry-level servers and networked storage applications. Serial ATA's ability to support a large array of drives is conducive to fixed-content server applications, such as e-mail, data mining, and data warehousing. Other applications include CDs and DVDs, CDRWs, high-capacity removable devices, optical drives, set-top boxes, tape devices, and zip drives.
Pricing patterns
Serial ATA's success depends on its adoption by PC makers, which will help move the interface into the high-volume, mainstream market, said iSuppli analyst Bill Bernard. "The technology has the potential to provide for cheaper hard drives for cheaper storage."
Although industry watchers are in unison regarding Serial ATA's prospects for addressing a large segment of the storage interface space, they are more cautious about predicting price points and revenue for drives or silicon.
For a preview of silicon pricing patterns, take a look at the target markets, said Vikram Karvat, director of marketing at ServerWorks Corp., Santa Clara, Calif. "On the drive side, the criterion is cost, cost, cost," he said. "Desktop margins are also razor thin. Devices for server applications will be lower volume and cost more."
John Monroe, an analyst with Gartner Dataquest in San Jose, estimates that Serial ATA drives are now priced $4.50 to $7 higher than Parallel ATA drives, and he anticipates price parity in 18 months, if not earlier.
"When they're in massive volume, cost will come down," Monroe said. "We'll see real volume as Intel makes its chipset changes."
Intel's interest
In April, Intel Corp., Santa Clara, introduced its first chipset incorporating serial ATA into its I/O controller hub. The 875P, formerly known as Canterwood, is a high-end companion chipset to the Pentium 4. Intel's Springdale, another Pentium 4 chipset due for release this quarter, will have similar functions, including Serial ATA, but be geared for more mainstream applications, which will help jump-start volume shipments of products with the interface.
Intel has an interest in seeing Serial ATA take off because the silicon giant is moving to 0.9- and 0.11-micron technology, which does not support 5V parallel storage interfaces, Monroe said. "Smaller transistors need 3V serial technology."
Drive makers and Intel want to shift as quickly as possible, Monroe said. But other chip companies developing products around the Intel chipset, as well as PC OEMs and other Serial ATA adopters, including optical drive makers, have different goals, which could cause some delays.
Adoption will accelerate when prices drop as the industry shifts from a two- or three-chip to a single-chip solution. Early offerings of the emerging interface technology use interim solutions, which typically include a standard Parallel ATA interface between the Serial ATA interface "bridge" chip and the hard drive SoC, which limits the data throughput on the Serial ATA cable to 100Mbytes/s.
This strategy often requires a minimum of two chips and consumes more power. On the plus side, some silicon vendors use this interim technology to debug new integrated devices they are developing.
A bridge may be sufficient for some applications, however. Philips Semiconductors, Sunnyvale, Calif., has introduced a parallel-to-serial bridge for optical storage applications, which will adopt the serial interface later than hard drive and PC makers, according to Sunil Nethisinghe, general manager of the company's Storage and Imaging Interconnectivity Group.
While simple cables and fewer pins are attractive in optical storage applications, they need speeds of only 60 to 70Mbytes/s, rather than Serial ATA's 150Mbyte/s capability.
Philips Semiconductors will go the integration route next year, which will satisfy the cost-sensitive optical drive sector, Nethisinghe said.
The first implementations of Serial ATA, which carry a price premium, are low-volume niche applications, primarily in the RAID area and targeted at build-your-own computer enthusiasts. The early implementations are benefiting from the connectivity advantages of Serial ATA 1.0.
The Serial ATA II extension to the specification takes the interface into the server realm by adding enterprise-class features, such as improved enclosure management and native command queuing, which enables several commands to be sent to the drive at the same time to execute at once. Port-multiplier capability, in which several drives can be connected to just one host port, is also part of Serial ATA II.
Serial ATA II is backward-compatible with 1.0 and offers a boost in transfer rate of 3Gbits/s from 1.5Gbits/s. Drives designed for Serial ATA II applications will be available next year, and chips for those drives are coming out this year. The enhanced functions will make Serial ATA more like its higher-end counterpart, Serial-attached SCSI (SAS).
Serial ATA will dominate in the hard drive space by 2006, with shipments outpacing higher-end alternatives such as Fibre Channel and SAS, according to iSuppli data. The aim is for Serial ATA to have parallel SCSI-type performance at ATA cost, said Mark Hartney, director of technical marketing for storage semiconductors at Silicon Image Inc., Sunnyvale. "Serial-attached SCSI is not here yet and will continue to have a premium because it won't benefit from volumes."
iSuppli analysts forecast that 3.3 million SAS drives will ship in 2005. They expect SAS offerings with a data rate of 3Gbits/s around mid-2004, and its parallel predecessor to be phased out over the next four years.
Other interfaces
SAS is designed to be compatible with Serial ATA and shares some of the same advantages, such as its point-to-point topology, fewer signal lines and board traces, and thinner cables for improved airflow, according to an iSuppli report.
SAS will complement more than compete with Serial ATA, according to IDC's Reinsel. "Parallel ATA is already in traditional workstations," he said. "We will see Serial ATA there; it will encroach in areas where performance is not the primary metric. SAS is not quite as certain. It has competition from Fibre Channel."
Others say it's unclear how SAS will affect Serial ATA market share and pricing. Chip companies, nevertheless, are hedging their bets by developing devices for all three interfaces.
"It's hard to say what will happen with Serial-attached SCSI, Serial ATA II, and Fibre Channel, whose prices are coming down--all compete for the enterprise market," said John Williams, strategic marketing manager for storage networks at Marvell Technology Group Ltd., Sunnyvale.
Marvell is sampling a 3Gbit/s Serial ATA II bridge chip that also supports SAS and Fibre Channel interfaces. The device, which includes Marvell's next-generation physical-layer transceiver architecture, will be incorporated across the company's disk drive SoC, storage networking, and custom ASIC solutions.
Also addressing the three serial-interface standards, Agere Systems Inc.'s Serial Storage Interface Platform (SSIP), a building block for drive SoCs and ICs as well as host-side ASICs, is designed to support current and next-generation data rates for each, including 1.5- and 3Gbit/s speeds for Serial ATA and SAS implementations and 1.06, 2.125, and 4.25Gbits/s for Fibre Channel networked drives.
Using the SSIP, Agere said it is developing an integrated SoC with an unnamed customer; the device is scheduled for third-quarter production, according to the Allentown, Pa., company.
STMicroelectronics Inc., which also expects to have an integrated SoC in the third quarter, is taking a different tack. ST's Serial ATA PHY transceiver core can be customized for Fibre Channel and SAS applications. Not combining the three interfaces in one core reduces die size and cost, said Paolo Cocchiglia, SoC senior marketing manager at ST in San Jose.
Tough transition?
The Serial ATA technology transition could prove challenging for some, Dataquest's Monroe said. "It's making a break with tradition--different connectors, voltages, and microcode. That could be a market inhibitor."
Jim Rubino, product line director for Serial ATA products at Vitesse Semiconductor Corp., Camarillo, Calif., agrees: "Time-to-revenue is a big issue, although it's not out in front publicly. Taking a jump up in functionality puts a whole new spin on things."
However, those "on both sides of the cable," he said, worked together closely to solve initial challenges such as interoperability. Anticipating interoperability issues early on and hashing them out has been key, according to Rubino, co-founder of APT Technologies, now part of Vitesse, and an early member of the Serial ATA Working Group.
The physical interface, or SerDes, is the most difficult piece of electrical technology to implement, according to LSI Logic's Jones. "But it's fairly common to existing standards, so experienced ASIC vendors can leverage off existing SerDes technology," he said.
Bringing a high-speed interface with high-speed PHY requirements to market is no easy feat, Seagate's Noblitt said. It has been difficult for Serial ATA, as it was for Fibre Channel, he added.
"Speed itself is difficult to bring to market and to do so in a high-volume, low-cost environment. With Serial ATA, we met that challenge by being able to scale the technology into an acceptable package and bringing line geometry down from 0.18 to 0.15 to 0.13 micron."
Proponents of the technology maintain that the industry has successfully addressed the interface's initial challenges. Close collaboration among the players continues to be crucial, but that is not unusual with this type of implementation, they say.
Drive and chipmakers as well as others in the Serial ATA arena are working together the same way they did with the introduction of Parallel ATA, said Knut Grimsrud, technology initiatives manager at Intel and chairman of the Serial ATA Working Group. "It's just a new chip. Putting the word 'serial' in front of it doesn't turn the environment upside down.
"Serial ATA is the future storage interface for Intel and the rest of the industry," Grimsrud said. "It has a long roadmap."
