The Silicon Power Armor A66 (starts at $49.90 for 1TB; $129.99 for the 5TB model we tested) has two big things going for it as a portable storage solution. This external hard drive, clad in a rubberized sleeve and with a cover for its USB Type-A port, has some outdoor cred, offering shock, drop, and water protection. Its 5TB model sells for less than 3 cents per gigabyte, just slightly more than some other hard drives with no ruggedness features to speak of. The drive comes pre-formatted in NTFS for use with Windows machines, but although it can be reformatted for use with a Mac, not all of our Macs were able to identify it.

One Tough, Platter-Based Portable Drive

With all the exposure and hype that high-performance solid-state drives (SSDs) get, you might think that hard drives' days are numbered, but their high capacity and low cost per gigabyte keep them viable, especially in the enterprise market. They still have adherents among consumers, although they're considerably slower than even the slowest SATA-based SSDs. (Oddly, Silicon Power lists the A66 as an "External Game Drive," but gamers need not apply.)

Taiwan-based Silicon Power has provided good value in the M.2 internal SSDs that we've reviewed (the Silicon Power US70 and UD70). This is the first hard drive we've seen from the company, and in general we liked what we saw.

The 5TB Armor A66 seen here measures 0.9 by 3.8 by 5.5 inches (HWD) and weighs 11.6 ounces, the same as the 4TB model. The 1TB and 2TB versions are thinner (0.6 by 3.8 by 5.5 inches) and lighter (7.4 ounces) than the higher-capacity drives, though all are on the bulky side for portable drives. The photo below shows the 5TB (blue) and 2TB (yellow) units from above, so the difference in thickness is not obvious.

As befits a ruggedized drive, the Armor A66 has a corrugated black plastic top and bottom, with a blue rubber bumper encircling the sides. The bumper is grooved to hold the provided USB-A to USB-A cable. At the right side of the near short edge is a USB 3.2 Gen 1 Type-A port. The bumper has a rubber seal to cover the port when not in use.

Platter-based hard drives are inherently more fragile than solid-state drives due to their moving parts, but the Armor A66 is sturdier than most. Thanks to an internal anti-collision suspension system, it offers military-grade shock protection, meeting the MIL-STD 810G Method 516.6 Procedure IV test requirements for surviving drops of up to 1.22 meters. An IPX4 ingress protection rating means it's safe from splashing water, though it's not built to survive immersion and the X in the rating means it isn't rated for protection from dust.

Silicon Power doesn't provide any speed ratings for the Armor A66, but in our tests its sequential read and write speeds proved typical of a 5,400rpm SATA III hard drive. It costs a bit more than its non-ruggedized brethren. (At current retail pricing, the 5TB Armor A66 sells for 2.6 cents per gigabyte, while the 5TB version of the Editors' Choice-winning WD My Passport goes for 2.4 cents a gig.)

The A66 arrives formatted in NTFS for use with Windows computers. Silicon Power notes that you can reformat it for use with Macs. On an Apple Mac Studio running macOS Monterey, I was able to reformat into two Mac-compatible formats, ExFat and APFS, but when I connected the drive using either format to any of our 2016 MacBook Pro's USB-C/Thunderbolt 3 ports (using a Type-A-to-C cable), the macOS 10.15 Catalina laptop was unable to recognize the drive. Thus we were not able to try the Mac-based BlackMagic and folder-copy tests that we run on most external drives.

Unlike the 5TB WD My Passport and several other portable hard drives, the Armor A66 lacks 256-bit AES hardware-based encryption.

Testing the Armor A66: Typical (Slow) HDD Speed

We were able to run our usual Crystal DiskMark and PCMark 10 Overall storage tests on our Intel X299-based testbed with the A66 formatted in NTFS. Its sequential read and write speeds proved typical of a 5,400rpm platter-based drive and fell within the narrow range of values shown among our comparison drives. The one drive in our chart with higher scores, the Seagate FireCuda Gaming Hub, is a 7,200rpm device.

Only two of our comparison hard drives ran our latest PCMark 10 benchmark, which tests a drive's speed in performing routine tasks such as loading programs and games; the rest of the drives ran a previous version. The A66 had the lowest score of the three.

A Ruggedized Drive for Data Safety On the Go

Available in versions up to 5TB, the highest capacity currently available for a portable hard drive, the Silicon Power Armor A66 offers some protection from drops (from desk or pocket height) and rain. You do pay a little more for these ruggedness features than you will for the likes of the 5TB WD My Passport, our portable hard drive Editors' Choice, and the A66 lacks the WD's hardware-based encryption (and its Mac compatibility proved dicey). Still, it's a good choice as a hard drive that you plan to use outdoors or away from your desk.