The HS1 series: 1.8-inch SSD with the Micro SATA interface
The HS1 series: 1.8-inch SSD with the Micro SATA interface
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TDK Corp launched the "HS1" series, a line of 1.8-inch solid state disks (SSD) with the Micro SATA interface, targeting notebook computers and industrial devices.

The HS1 series comes in three models with storage capacities of 16, 32 and 64 Gbytes, respectively. The product uses SLC (single-level cell) NAND flash memory. It is the commercialized version of the prototype exhibited at CEATEC in 2007. Now that the qualification test by customers has been completed, the new SSDs are ready to be incorporated in industrial devices, the company said.

The disks are now available for volume shipment at sample prices of ¥200,000 (US$1,902, price may vary depending on country) for a 64-Gbyte model, ¥150,000 for a 32-Gbyte model and ¥90,000 for a 16-Gbyte model.

The company is planning to exhibit the series at COMPUTEX TAIPEI 2008, which runs from June 3 to 7, 2008 in Taipei, Taiwan.

Burst performance is 100MBps reading and 50MBps writing. To accelerate the writing speed, the disk has a four-channel bus, which extended the standard one- or two-channel bus, between the controller LSI and the NAND flash memory.

By time-dividing a single channel, two memories can be used simultaneously. The writing speed is equivalent to that of a standard product for a number of reasons, including the fact that the disk performs wear leveling to average out the number of rewrite operations per cell.

The power consumption in "Slumber Mode," where the disk is in a standby mode without reading or writing, is approximately 20mA. In regard to the controller LSI, the NAND flash memory control circuit and the SATA interface circuit, which are generally provided in two separate chips, are integrated in a single chip so that the power consumed by the signal line between the chips can be reduced, according to TDK.

The encryption method used in the disk is 128-bit AES. The disk also has a function to detect and correct errors up to 7 bits.

The product is equipped with "GBDriver HS1," TDK's proprietary NAND flash memory controller LSI. It was developed to increase the life of MLC (multi-level cell) SSD by reducing the number of rewrite operations through the optimization of block control in the NAND flash memory. But the controller LSI is also applicable to SLC SSDs.

The adoption of MLC NAND flash memory is required to develop a 1.8-inch product with a large capacity such as 128 Gbytes. However, the adoption of MLC memory does not drastically reduce the cost at present. Moreover, it is difficult to meet the level of durability that the users demand.

TDK conducted a test by simulating the access state of the SSD and HDD when various kinds of application software is running on a personal computer. As a result, the combination of MLC memory and the controller IC provided a rewrite life of 10 years (when operated 24 hours a day, 365 days a year), according to the company.

Even so, the level of reliability demanded by users could not be met, which is the reason why the company decided not to adopt MLC memory at this time. It is possible that TDK may employ MLC memory sometime around 2010.