Inside Intel's SSD

Posted at: Thursday 25th September 2008 by James Morris

The technology behind Intel's revolutionary next-gen storage device

The solid-state drive (SSD) has improved in performance over the last few years, and the fastest examples have been edging ahead of hard disks in performance. However, Intel’s new SSDs have burst onto the scene like a streaker at a royal wedding. We uncover the secret behind their much faster performance.

CUSTOM CONTROLLER

The primary difference is found in the controller chip, which receives data from the S-ATA II bus and allocates it to the individual Flash chips. Whereas most manufacturers buy this chip from another manufacturer, Intel has created its controller from scratch, thanks to its in-house expertise in this kind of technology.

This is an important factor, as the controller chips of previous SSDs haven’t traditionally been able to handle data at the speeds that Flash memory can deliver. Intel’s new controller removes this bottleneck, and interestingly, also supports Native Command Queuing (NCQ), allowing it to stack up to 32 requests to reduce the latency caused by the host PC waiting to issue new commands.

MULTI-LEVEL CELLS

The first Intel SSDs to hit the market use multilevel cells (MLCs). These have multiple voltage states, allowing them to store more than one bit of data per cell. The most common variety has four states and can store two bits of data per cell.

In contrast, most of the SSDs currently on the market use single-layer cell (SLC) memory. As MLCs store more data per cell, their capacity is cheaper, which is why Intel’s 80GB SSD costs only a little more money than many 32GB models.

MLC technology isn’t perfect. Its write performance is slower than its read speed. Also, while all Flash memory cells deteriorate over time, the more complex voltage levels of MLCs mean that they’ll endure ten times fewer write cycles than SLCs.

To combat this, Intel’s controller also makes efficient use of this reduced lifespan, so it can still quote a MTBF of 1.2 million hours. This is lower than the two million hours often quoted for SLC-based SSDs, but equal to most enterprise-level conventional hard disks and twice the usual value for consumer disks.

THE FUTURE

Not all Intel SSDs will use MLCs, however. Intel’s 32GB and 64GB X25-E Extreme will make use of SLCs, boosting its write performance to 170MB/sec while maintaining a read speed of 250MB/sec.