20 August 2008, 15:42

IDF: Fast SSDs

Solid-state disks (top) store data on flash chips rather than on the rotating magnetic platters found in conventional hard disks (bottom). While Intel only presented some rather dated SSDs with PATA interface at Computex, the chip manufacturer is flexing its muscles at the IDF: The two X25-M and X18-M solid-state disks for desktop PCs and notebooks hold 80 or 160 Gbytes of data and are super fast, reaching data transfer rates of up to 240 Mbytes/s during read access. While their write access speed of 70 Mbytes/s is slower than that of current hard disks it is still quite acceptable. Intel has tuned SSD performance by running ten channels in parallel. The exact number of MLC chips – in 50 nm technology – per channel has not yet been revealed.

The X25-E Extreme is a slightly faster SSD, intended for servers. It reaches up to 250 Mbytes/s while offering access speeds of only 75 microseconds. At 32 and 64 Gbytes respectively it holds less data than its mainstream siblings. According to Intel it can handle up to 35.000 read operations per second. Write operations run ten times slower.

Intel now uses the SATA-II (revision 2.6) interface. Particularly noteworthy is the support of Native Command Queuing (NCQ) – with up to 32 simultaneous transactions – so far, hardly ever available with SSDs. Although NCQ was originally developed to minimise the jumping of the read/write heads in conventional hard disks, the technique for reorganising requests also increases the performance of flash memory: Write access in particular is restricted to niblets of 2 to 4 Kbytes in flash cells. If the write operation requires existing data to be overwritten, things become even more elaborate: Data can only be deleted in blocks (256 to 512 Kbytes), which may require existing data to be relocated beforehand. The SSD can use NCQ to inspect the command queue and avoid relocating data that is due to be overwritten.

Intel plans to offer SSDs in 1.8" and 2.5" format. The power consumption of the X25-M and the X18-M is designed to be between 150 mW for typical PC operation and 60 mW when idle. Intel specifies an operating temperature of between 0°C and 70°c.