What is the difference between the Xiaomi 4A 100Mbps and gigabit versions of the Xiaomi router? Uncle San's 300 Mbps broadband only runs 90 Mbps. After checking the router, you can see the labels and you'll understand everything

last month, my third uncle sent me a WeChat voice message, with TV background music: "Nephew, is the 300MB installed at home fake broadband?" After testing with my phone, it's only 88 megabytes." My first reaction was that the optical modem was plugged into the wrong port or the network cable had four cores. On weekends, I brought my laptop over, plugged the network cable directly into the router's LAN port, and when the negotiated speed popped up, I didn't need to check anymore—100Mbps. Flipping through the router, I checked the bottom label: Xiaomi Router 4A, with a small line of text at the end: 100M.

Before

going, I asked him over the phone to do two steps: check the optical power in the background via optical modem, minus 21, and the optical path is fine; Standing in front of the router, I connected the 5G band and tested: 88 Mbps; plugging the computer network cable directly into the LAN port tested: 92 Mbps. Wired cables are stuck around 90 Mbps, a very typical number—the bottleneck isn't in the air or the walls, but in a place where all traffic can't be avoided. Upon arrival, they flipped through the labels and closed the loop.

to clarify first: 4A is one name, two machines

this matter started in 2018. Back then, competition in the 100-yuan router market was fierce. Xiaomi made two versions of 4A and sold them simultaneously, both with identical names—'Xiaomi Router 4A'—one 100Mbps version, one gigabit version, with prices differing by several dozen yuan. The "4A" that the store calls it "4A" ultimately depends on the stock and luck when you actually get it. This machine was given by the town's computer shop back then with broadband, so naturally, the cheaper one was included.

I made a table for the two versions of the accounts, so you can immediately see the difference:

note the wireless line; both versions use the same dual-band AC1200. Here's the tricky part: just looking at the WiFi name, signal bars, and background interface, the two machines are almost identical, even the background screen looks the same. The difference lies in the network ports you can't see and the chips inside the belly.

gap is not just one network port: the chip is one generation behind

100Mbps version's MT7628DA is MT7621A's predecessor: single-core 580MHz versus dual-core 880MHz, with only half the memory, and at full load, the NAT forwarding margin is on a completely different scale. The Gigabit version also adds independent PA and LNA, so the same-house signal and wall attenuation performance are much better. You might not notice it when browsing your phone daily, but when your home has many devices, some people watch livestreams, some are downloading things, and the 100Mbps version lags first.

for tinkerers, this gap is even more fatal: the Breed and firmware on both units are completely incompatible. MT7621A solution ecosystem is very mature; if you want to copy tutorials on the 100Mbps version, you just reboot endlessly. So for those practicing buying second-hand goods, mistakenly identifying the wrong version is basically spending a whole night of effort.

Third Uncle added a useful tip: this machine feels hot to the touch in summer, and every few nights it breaks out. If it does, he unplugs and replugs the power. Single-core 580MHz is usually a bit high in load, and if the cooling is poor, disconnections will follow. This isn't an isolated case. For ultra-high-spec small machines like the 100Mbps version, it's normal for the Tianyi thermal system to surrender stability first.

Three Tips for Identifying Brands: Don't Trust Sellers, Trust Labels and Negotiation Speed

first trick: flip the bottom tab. The label on the 100MB version has "100M" next to the model number, which the Gigabit version does not have. That's how Third Uncle recognized this machine—it only took ten seconds. Look at the brand-new, unopened packaging. The box clearly displays the words "Gigabit Edition"; if it doesn't, it's the 100M version.

second trick: plug your computer into the network cable to check negotiation speed—this is the most accurate. Plug the network cable into the LAN port and wait two seconds. Windows checks the network connection status, while Mac checks the link speed in network settings. Negotiate that 1000Mbps is gigabit version, 100Mbps is 100Mbps. The whole process takes thirty seconds—more civilized than teardown, more reliable than asking sellers—anyone can type 'Gigabit version' on Xianyu.

third tip: Beginners ask about firmware versions. The Gigabit version itself is divided into two generations: V1 and V2. V1 uses firmware starting with 2.28.x, and you can follow a ready-made open-source solution; V2 requires you to compile your own firmware, so beginners should avoid it. Before buying, have the seller take a screenshot of the backend system status, making the version number clear at a glance and saving you from getting confused.

90 is how it came about: a hundred mega-mouths are the main gateway of the whole family

Uncle San's dissatisfaction was: "My phone is connected to 5G WiFi, the signal is full, but it's only 90 Mbps?" I showed it to him: WiFi is from home to the router, and it's really fast. The 5G band can reach 867 Mbps. But when you go from the router to the carrier, the whole family's data has to be squeezed through the 100MB gate at the WAN port. No matter how lively it is inside, it's just a narrow winding path outside.

100Mbps the theoretical maximum download speed is 12.5MB/s, and after deducting protocol overhead, a stable 90 to 95MB is the normal level for this barrier. Third Uncle's home is 88 trillion, not a cent more, not a little less, just stuck at the ceiling. This numerical feature is exactly the same as the problem of the optical modem being inserted into the wrong 100Mbps port. I wrote a comparison table in my article the optical modem about gigabit and hundredMHz ports. If your home network is stuck around 90Mbps for a long time, first suspect the 100Mbps segment and don't blame the carrier first.

As for how to convert megabytes and MBs, and how much broadband is sufficient for your home, I previously calculated the details in the article how many megabits broadband you can install in . In short: dividing the Mbps by 8 is what you see as download speed.

What use do these two cars have left for

2026

to start with the conclusion: when the main router is the main router, both units fail the standard. As mentioned earlier, the gigabit version has no issues, but dual-core 880MHz with several hundred Mbps broadband running basic NAT is manageable. But when you have 30 or 40 devices at home and turn on some additional features, it becomes exhausting. In the end, Uncle San listened to me, spent 129 yuan to buy a AX3000T, plugged in a test of 294MB, and apologized to the carrier on the spot.

but just throwing it away isn't worth it—each has its own destination. The most suitable position for the 100Mbps version is 2.4G IoT private network : vacuum cleaners, cameras, and temperature and humidity meters—devices that only recognize 2.4G and have low bandwidth—are managed by a separate network to keep them in place, preventing conflicts with mainline phones and computers. My old AC2100 was modified this way. I've written about the process of AP feeding 14 smart devices , and the 100Mbps version just follows it. After all, each device only has a few hundred KB of bandwidth. Why do old devices have their own network? the accounts of old equipment occupying idle time you can understand once you calculate it.

Gigabit version is worth getting for practice. The MT7621 with 128MB of RAM is a classic foundation for flashing phones. The second-hand market price is forty to seventy to eighty yuan, and flashing OpenWrt as a bypass router or running lightweight plugins is more than enough. If you want to start flashing, first look at how unlock the SSH, then follow the process AX3000T the OpenWrt setup; Even older MT7620 platforms have been used as bypass routers, my R3 flash Padavan is still in service at my mom's house.

also mention the 4C. It's a re-engineered version of the 4A 100Mbps version: the same MT7628DA comes with 64MB of RAM, cutting the entire 5G band down to 2.4G single-band 300MB, while the network port remains 100Mbps. Today, some stores even sell it as a "new Xiaomi model" for forty to fifty yuan, but as the main router, it's really ineffective. Like the 100Mbps version of the 4A, it's only suitable for carrying IoT devices. If I really want to get a new Taiwan for my parents' home, I've written about the base and version pitfalls of the hundred-yuan AX3000T I've used for two years , so just follow and avoid them.

give me an order at the end

have 4A bandwidth, first check the label to recognize the version, then check the broadband at home: below 200 Mbps and with few devices, the 100 Mbps version is still acceptable; With 300 Mbps broadband, don't hesitate to switch directly. For second-hand buyers, triple questions ask—100MB or gigabit, V1 or V2, firmware version. If the seller can't answer, they ask them to take a screenshot of the backend. If you're buying a new phone, make sure the packaging is labeled as 'Gigabit Edition' or simply buy AX or BE series from the past two years—don't gamble on twins with the same name. My third uncle's 100Mbps version is now at my cousin's house with six smart devices, retired and rehired, and is doing quite well.