The picture below is an excellent illustration of the differences between the physical levels of various external and internal standard versions:
This is the price you have to pay for longer cable and its ability to work normally in tougher working conditions: for stable data transfer rate the signal level of the transferring part of all external standard versions had to be at least doubled, while the receiving part remained almost unchanged, they only increased the upper part of the working amplitude. At the same time, the amplitude range grew considerably wider: if it stayed between 400-6—mVppd for Gen1i, then for Gen1x and Gen2x it rested between 800-1,600mVppd respectively.
External Cable Length and Features
To be fair I should say that high-quality screened cable will be a nice addition to the internal SATA devices, too. One of the first developers, who paid serious attention to cables and their characteristics, appeared Western Digital Company, which is also shipping their own cable to the market today: WD SecureConnect:
The requirements listed in the “Serial ATA II Cables and Connectors Volume 2” specifications say that the cable for external SATA devices shouldn’t be longer than 2 meters and the cable itself should contain an additional integrated signal channel responsible for coordination of up to four external devices. This serial connection scheme is expected to be the most demanded for industrial and server devices, such as RAID subsystems, for instance.