ASUS USB-AC51 AC600 Dual-Band USB Wi-Fi Adapter: features and specs

The ASUS USB-AC51 is a compact USB Wi-Fi adapter that adds 802.11ac dual-band wireless to a computer. It suits desktops with no wireless card and older notebooks whose built-in Wi-Fi only handles the 2.4GHz band. ASUS describes it as the smallest 802.11ac USB Wi-Fi adapter on the market. Here is what the specs mean.

What AC600 and dual-band mean

"AC600" is a class label that combines the maximum speeds of the two bands. The adapter works on 2.4GHz and 5GHz, and you can choose between them. ASUS lists speeds of up to 433 Mbps on the 5GHz band. Those are theoretical link speeds under ideal conditions; real-world throughput is typically lower and depends on distance, walls, interference and the router.

The two bands behave differently. The 2.4GHz band reaches farther and passes through walls more easily, but it is crowded and slower. The 5GHz band is usually faster and less congested, but its range is shorter. Having both lets you pick whichever works better in a given room.

Upgrading an older computer

ASUS calls this an instant upgrade to next-generation 5G Wi-Fi for desktops and notebooks. That phrase refers to the 5GHz Wi-Fi band and the 802.11ac standard, not to mobile 5G. The adapter plugs into a USB port, so there is no need to open the computer. Adding it can help an older machine connect to a modern dual-band router and enjoy the 5GHz band.

Operating system support

The listing says the adapter supports Windows, Mac OS X and Linux. Which versions are covered, and whether a driver must be downloaded, depends on the operating system. Check ASUS's support pages for the version you run, especially on the latest releases.

Service prioritization

The listing mentions an extensible design that enables service prioritization for data. This is a general reference to traffic prioritization, where time-sensitive data such as video calls can be handled ahead of other traffic. Whether this makes a noticeable difference depends on your network and router.

Size and weight

The adapter weighs about 0.2 lb (roughly 90 g) in the listing. Its small body makes it easy to carry between computers. The listing states the country of origin as China.

Who it suits

It suits anyone who needs to add Wi-Fi to a desktop, replace a failing wireless card, or bring an older notebook onto 5GHz networks. It is less suited to people who need the latest standards such as Wi-Fi 6, which this adapter doesn't offer.

What to check before you buy

• Router compatibility: confirm your router offers a 5GHz band if you want the faster speeds.
• USB ports: the adapter needs a free USB port, and a port with enough bandwidth for the speeds you expect.
• Operating system: check the driver support for your exact version of Windows, macOS or Linux.
• Placement: a port at the back of a desktop can be blocked by a case; a short extension lead can help.
• Speed expectations: 433 Mbps is a maximum, and your internet plan may be the limit anyway.
• Newer standards: if your router uses Wi-Fi 6 or Wi-Fi 7, this adapter will connect using 802.11ac.

The short version

• A compact USB 802.11ac Wi-Fi adapter rated AC600.
• Selectable 2.4GHz and 5GHz bands, with up to 433 Mbps on 5GHz.
• Works with Windows, Mac OS X and Linux, according to ASUS.
• Adds 5GHz Wi-Fi to desktops and notebooks without opening the case.
• Weighs about 0.2 lb.

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