Electronic Design

Make Some Room For New Storage Devices In 2008

Gone is the floppy disk. Magnetic media reigns supreme when it comes to capacity, and solid-state storage is everywhere. There is even a meeting of the minds with hybrid storage drives. High-capacity, high-definition (HD) optical drives are finally available too.

These technologies are creating new design opportunities because of improvements in the hardware’s cost, reliability, and performance. Yet challenges continue, such as new interfaces like Serial ATA (SATA) and the availability of legacy devices.

High-Capacity Optical
HD-DVD and Blu-ray aren’t new. But the availability of devices like Lite-On’s LH-2B1S Blu-ray drive in quantity make them viable for new embedded designs (Fig. 1). This is a particularly attractive option, as high-capacity, single-sided Blu-ray disks can hold 25 Gbytes.

SATA interfaces are the norm for these new drives, which also have higher throughput than DVD alternatives that tend to be IDE-based. DVD drives continue to improve, but lower cost and power requirements will be their edge.

This type of optical storage gains significant benefits from the consumer market, where high quantities continue to push down the price. Likewise, the availability of writable media at affordable prices makes data recording and distribution inexpensive.

Terabytes For Everyone
Capacity is still the name of the game for hard disks, and Seagate’s 7200.11 Barracuda leads the way with a 1-Tbyte capacity (Fig. 2). The jump to perpendicular recording over the past couple of years has significantly boosted capacity and performance. It will be interesting to see if this trend can continue.

A more significant trend will be the availability of IDE-based magnetic storage. Most shipments are moving toward SATA and SAS (Serial Attached SCSI). The limited availability of drives with other interfaces will push up their cost. This will have implications on legacy support and maintenance as well as on the viability of designs that only support IDE and SCSI.

Another trend that has taken hold is security. Hardware-based, full-disk encryption is an option that is available for laptops whose drives are ideal for many embedded applications. There is still a disconnect between other chip-based security measures and these kinds of hard-disk drives, but this is likely to change as designers get a better understanding of system security.

The drive to put hard drives in automobiles is leading to a crop of rugged hard disks that will be especially useful for embedded designers. Likewise, drives optimized for streaming multimedia applications will be worth a look.

Solid-State Storage
The USB flash memory stick has effectively killed the floppy, and this class of storage has done more to change design options for developers than any other technology. Flash’s compact size and lack of moving parts has opened up designs from MP3 players and cell phones to secure, airborne logging systems.

Keep an eye out for high-capacity storage options like SanDisk’s 64-Gbyte SATA 5000 2.5-in. solid-state drive (SSD) (Fig. 3). The move to new interfaces like SATA will be important as throughput continues to rise. Flash drives are already faster than magnetic media.

Designs like Act/Technico’s Secure PMCStor secure storage take advantage of flash, adding features such as secure erase (Fig. 4). As with magnetic storage, built-in encryption support is also showing itself in solid-state drives.

IDE- and USB-based flash storage devices also are coming on strong in the embedded arena for non-removable storage inside the box. Capacities are so high, it’s easy to replace a hard-disk drive with a device that plugs directly into the motherboard and provides the same boot and execution performance as a much larger device. USB-based storage also is becoming more popular with microcontroller developers that have USB interfaces built into their chips.

Mixed Bag
Solid-state front ends for magnetic hard drives were available last year, but quantities and capacity will be up this year, as with Seagate’s Momentus 5400 PSD. Also, Samsung’s HM08HHI has 80 Gbytes of storage with a 256-Mbyte oneNAND flash memory front end that is transparent to the system (Fig. 5).

Now that availability is no longer a concern, the rate of adoption should increase. Yet system performance still will be an issue. The potential advantage is large, but the actual advantage was initially less than expected. The main factor is the software utilizing the system, and that can easily be changed. This year will see more development on the software side to take advantage of these drives.

Indicating the potential, SCSI and SAS RAID controllers already have this type of capability. They incorporate the flash memory on the controller rather than in the drive, but the effect is the same. Improved system reliability due to flash memory use also will start to play a part as developers learn to take advantage of the architecture.

Storage Interfaces
As noted, IDE and SCSI aren’t going away. But they will be harder to find as optical, flash, and magnetic drives move to SATA and SAS. The migration at the processor chip set is almost complete, but the movement at the microcontroller level to these newer interfaces is slower. This is partially due to the complexity of high-speed serial design compared to parallel IDE interfaces. Still, the advantages of the newer technology are clear.

At the lower end, SD/MMC and similar interfaces remain the mainstays. Multiple options are likely to remain, making the selection of interface and corresponding flash devices less clear.

So what else is there? Tape and holographic optical storage are in use, but they tend to be in very specific markets. For example, tape is still a workhorse for servers though their use in embedded applications tends to be very limited.

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