USB/FireWire/eSATA: 2.5” And 3.5” Storage Options
Several years ago, users had to replace their PC’s hard drive or install an additional one to increase storage capacity. However, today there are many options with which to expand storage space by adding external devices, including 2.5” portable drives with 640GB (and soon 1TB of capacity) and 3.5” products that offer up to 2TB on a single hard drive. Meanwhile, enthusiasts might opt for a RAID-based storage box with several hard drives. However, since performance depends on the interface, we decided to look at two popular drive options to help you choose the interface that works best for your application: high-capacity USB 2.0 and a combo product that also offers FireWire 400, FireWire 800, and eSATA.
2.5” vs. 3.5”
The image above also shows a 2.5” portable drive. Everything we’ll discuss applies to 2.5” portable drives, as well as to 3.5” external hard drives. Using USB 2.0, both form factors deliver similar performance, while 2.5” models might not require an additional power supply. However, there are only few 2.5” eSATA drives, and you can expect 2.5” drives to deliver less throughput than their 3.5” brothers.
USB Against the Rest
USB 2.0 has been available for many years and it’s not an exaggeration to say that this interface is available on each and every computer--whether we’re talking about desktop PCs, notebooks, or servers in the Windows world or on Apple systems. And although USB 2.0 is reliable, highly compatible, and easy-to-use, it does have a disadvantage that forced the industry to move on: USB 2.0 is limited to 480 Mb/s, which translates into 30-35 MB/s maximum bandwidth for typical storage applications. This is certainly more than enough for most device types and for casual storage use, but as soon as you want or need to move many gigabytes of data on a regular basis, you’ll want more throughput.
FireWire (or IEEE 1394) has been around for many years as well. The initial standard, FireWire 400, or 1394a, provides 400 Mb/s throughput and isochronous transfer, which is necessary for real-time transmission of data--something you would want for digital video, for example. FireWire 800, or 1394b, doubled the throughput to 800 Mb/s, but neither of the two FireWire specifications really became mainstream. Although FireWire is popular and widespread, it is not even remotely as prolific as USB.
Finally, we have eSATA, which stands for external Serial ATA (SATA). This is a modification of the SATA standard that most computers use to attach hard drives and optical drives, adjusted to support longer cables for external devices through modified electrical specifications. In addition, connectors are physically different to avoid mixing them up. The cable length of up to 2m is sufficient for storage applications, but both FireWire and USB still support longer cables that are 4.5m and 5m in length. However, eSATA is as fast as internal SATA, which translates into a maximum of 300 MB/s for 3 Gb/s SATA connections.
Future FireWire standards, such as 1394d, could reach 6.4 Gb/s, but these will probably not be very mainstream. USB 3.0 (also known as SuperSpeed USB) is specified at 4.8 Gb/s and has the potential of reaching effective throughput of up to 400 MB/s. The standard is in the process of deployment, but it will take at least one more chipset generation in one or more years until we can assume that most systems will actually be equipped with USB 3.0. eSATA at 6 Gb/s also has the potential to offer additional bandwidth, but we believe that USB 3.0 will dominate.
Combo Drives
There are hundreds of portable and external hard drives that utilize the USB 2.0 interface. Most of them deliver similar performance, so there is not much risk associated with opting for one product over another. However, if you go for a high-capacity product, it can take several hours for a storage device to read or write hundreds of gigabytes of data.
Drives that combine USB 2.0 with additional interfaces seem to offer a good compromise--FireWire 800 enables additional throughput and eSATA promises to deliver native hard drive performance without any bottleneck for modern storage products. Today we're comparing a 2TB USB 2.0 and a 1TB quad-interface combo drive, analyzing the performance differences.
