2.5" Vs. 3.5" - Desktop Vs. Notebook - HDD Vs. RAM Vs. Flash
Most of the Flash SSD drives that are available today the were released to the market in a 2.5" form factor, which is the dominant size for the notebook mainstream. Ultra-portable devices sometimes utilize 1.8" drives, so do portable MP3 players such as the classic iPod and others. While 1.8" hard drives at up to 120 GB are spacious, fast enough and sufficiently cost effective for mutlimedia applications, storage perforance is the only issue that still seperates desktops from notebooks if we disregard the display. Therefore it makes a lot of sense to replace a 2.5" notebook drive by a 2.5" Flash SSD. Let's look at the reasons.
Due to their smaller platter diameter, 2.5" drives do not reach the same absolute media velocity as 3.5" hard drives, although the relative rotation speed may be the same (5,400 or 7,200 RPM). This is the main reason why notebook drives max out at less than 70 MB/s. This difference is noticable when you compare to a 3.5" drive's 80 to 115 MB/s maximum. The better the transfer rates, the faster you'll be able to start Windows or applications, the next level of your favorite 3D shooter, a Visual Studio project, or copy files from/to the drive.
Since data oftentimes is not written sequentially, but distributed across different sectors all over the discs, a drive's access time is also important. If a drive has to work on several requests at the same time, access time and I/O performance, which is based on typical professional access patterns, comes into the equation. Hence, the ideal hard drive should deliver maximum data transfer rate at minimum average access time.
The best technology to answer this idealistic requirement would be DRAM, which currently offers several gigabits per second throughput (depending on the bus width and clock speed). At the same time, cycle and access times of Random Access Memory are only important if DRAM is actually used as main memory. As a storage solution, the access time of memory is effectively nonexistent. However, DRAM has one disadvantage, which disqualifies it as a hard drive replacement: it is volatile memory, which cannot preserve the transistor states and the stored information once the power is cut off. Solutions that we can actually recommend are usually unaffordable for the vast majority of us; the HyperDrive 4 by HyperOS/Accelerated Logic delivers exactly what an enthusiast wants, but both the device and the required memory modules make it far too expensive.
Everyone who followed the capacity and price developments in the Flash market knows that this memory technology has shown the largest price cuts over the last few years. SD memory cards with 2 GB capacities have almost reached $10 at many e-tailers and even 8 GB USB 2.0 Flash drives will break the $50 line shortly. So, why not using Flash as a permanent storage medium? We looked at a first 32 GB Flash SSD from Samsung over a year ago. This prototype was based on UltraATA/66 and delivered nice performance, but it still was far too expensive to ever make it the mainstream. The next big step was availability of faster 32 GB Flash SSDs with SATA/150 interface earlier this year. SATA is the dominating interface for permanent storage devices, both in notebooks and desktop PCs. SanDisk was the first memory maker to provide a sample, and the Flash SSD SATA 5000 2.5" did well in our benchmarking suite. However, Flash does have a significant disadvantage: it's capabilities at random access are severly limited. This isn't much of a problem for regular users; they will still get a noticable performance boost out of a Flash SSD. However, frequent random access would still be executed faster by a fast, conventional hard drive than by a Flash SSD.
At price points of $300 and up, 32 GB Flash SSD are attractive to power users, but they are far from being perfect. The limited capacity of 32 GB for me is a no-go for my notebook, as I'd have to carry an external hard drive to have all my important data with me. But not everyone requires 32 GB when on the road, and a fast system drive would always work well in a desktop PC, where you can add a high-capacity storage hard drive at any time. This is probably exactly the scenario Mtron aims at, since its new 32 GB 2.5" SSD is priced at clearly above $1,000 - but it also broke all speed records.