Review: Samsung SSD 840 EVO (120GB)

Introduction

And here we were, staring multiple SandForce drives in the face, thinking solid-state innovation had ground to a halt. How wrong we were. Boffins at some of the biggest names in the industry have proven that there's plenty of room for improvement, with Intel introducing a new level of consistency across the SATA 6Gbps interface and Crucial showing us that high-capacity SSDs needn't cost the earth.

Up next? Samsung, who's here to tell us that affordable, low-capacity drives don't have to offer second-rate performance when compared to larger drives in the same range. It's a familiar problem, and one what does need tackling. Take the recently launched Crucial M500 as an example - great drive, but the low-cost 120GB model takes a 68 per cent performance hit in terms of sequential write speed when compared to the range-topping 960GB drive.

It's that massive gap that Samsung is attempting to narrow with the new 840 EVO. Designed as a successor to the popular 840 Series, the EVO drive slots in below the top-of-the-line 840 PRO and aims to offer an affordable upgrade path to those looking to take their first steps into solid-state territory. At launch, the EVO Series drive will be available in a choice of 120GB, 250GB, 500GB, 750GB and 1TB capacities, with prices ranging from £87 to £510.

The read and write speeds of the spacious 1TB drive are rated at 540MB/s and 520MB/s, respectively, but what's interesting is that the cheap-and-cheerful 120GB model isn't far behind - it claims to offer 540MB/s reads and 410MB/s writes, which is impressive for a low-capacity drive.

So how has Samsung managed to loosen the previously tight link between performance and capacity? As we know, today's SSDs utilise multi-channel controllers and are able to offer optimal performance when numerous NAND memory chips are interfacing with the processor in parallel.

Taking a look inside the 120GB EVO SSD suggests that the problem should, if anything, be exaggerated. Samsung has just a pair of 19nm NAND memory chips (one either side of the mini-PCB) hooked up to a triple-core controller and a modest 256MB onboard DDR2 cache.

Creating all the components in-house is an obvious advantage - they should work in harmony when set to task by Samsung's proprietary firmware - but two NAND chips, a multi-channel controller and a small DDR2 cache is hardly a recipe for blazing speed. There has to be something else afoot, and there is; both in terms of hardware and software.

First and foremost, Samsung has increased the speed of the controller. The new chip, dubbed MEX, is based on the same triple-core ARM Cortex R4 architecture, but is now clocked at 400MHz; a full 100MHz faster than the previous MDX. A bump in core frequency is typically the way to increase performance, but the 840 EVO's real party tricks are two new technologies dubbed TurboWrite and RAPID (Real-time Accelerated Processing of I/O Data) Mode.