Those dissatisfied with the performance of mechanical storage solutions can tap solid-state storage devices that substitute silicon for spinning platters. Such devices shed the mechanical shackles that limit hard drive performance, but they've hardly been affordable options for most users. Then Gigabyte unveiled the i-RAM, a $150 solid state-storage device that plugs directly into a motherboard's Serial ATA port, accommodates up to four run-of-the-mill DDR SDRAM modules, and behaves like a normal hard drive without the need for additional drivers or software.
Gigabyte first demoed the i-RAM at Computex last summer, and cards have finally made their way to the North American market. One has also made its way to our labs, where it's been packed with high-density DIMMs and run through our usual suite of storage tests. Read on for more on how the i-RAM works, what its limitations are, and how its performance compares with a collection of single hard drives and multi-disk arrays.
The i-RAM's greatest asset is easily its simplicity. Just populate the card with memory, plug it into an available PCI slot, attach a Serial ATA cable to your motherboard, and you've got yourself a solid-state hard drive. There's no need for drivers, extra software, or even Windows—the i-RAM is detected by a motherboard BIOS as a standard hard drive, so it should work with any operating system. In fact, because the i-RAM behaves like a standard hard drive, you can even combine multiple i-RAMs together in RAID arrays.
Gigabyte equips the i-RAM with four DIMM slots, each of which can accommodate up to 1GB of unbuffered memory. The card is sold without DIMMs, giving users some flexibility in how it's configured. However, most will probably want to shoot for that 4GB maximum. After all, if you're going to have a solid-state hard drive, you want it to be as big as possible.
Be careful when adding memory, though. The i-RAM's DIMM slots are mounted on an angle to ensure that the card doesn't interfere with adjacent PCI slots, and there isn't enough room for DIMMs with thicker heat spreaders—at least not if you're planning on packing the card with four memory modules.
While tight DIMM spacing limits compatibility with thicker heat spreaders, it's not a major concern, because it's unlikely you'll want to waste high-end memory on the i-RAM. You see, the i-RAM's Serial ATA controller is limited to 150MB/s transfer rates, creating a bottleneck that will constrain performance long before memory speeds or latencies enter the picture. In fact, even DDR200 memory has ample bandwidth to saturate the i-RAM's Serial ATA interface.
Translating Serial ATA requests for a bank of four DIMM slots is no small task, but Gigabyte gets the job done with a Xilinx Spartan-3 field programmable gate array (FPGA) chip. The Spartan-3 is programmed to act as the i-RAM's memory controller, Serial ATA controller, and the link between the two, accomplishing three tasks with one piece of silicon. The single-chip solution is elegant, but it's also the source of the i-RAM's biggest limitations. For example, the memory controller doesn't support ECC memory or 2GB DIMMs, both of which would be useful. And then there's the Serial ATA controller's lack of support for 300MB/s transfer rates, which will probably be the card's most serious performance impediment.
Since it relies on volatile memory chips for storage, the i-RAM will lose data if the power is cut. Fortunately, the card can draw enough juice from a motherboard's PCI slot to keep its four DIMM slots powered, even when the system is turned off. The system does have to be plugged in and its power supply turned on, though.
To allow users to unplug their systems for periods of time and to protect against data loss due to a power failure, Gigabyte also equips the i-RAM with a rechargeable lithium ion battery that packs 1600 milliamp-hours of power. The battery charges while the system is plugged in, and according to Gigabyte, it can keep four 1GB DIMMs powered for more than ten hours. Battery life will vary depending on the i-RAM's memory module configuration, though. It's probably a good thing to back up anything you actually store on the drive, just in case.