What's the difference between AC600, AC1200, AC<n> wireless network adapters?

Question

I'm planning to buy a wireless PCIe or USB network adapter for 802.11ac but I don't understand the difference between AC600, AC1200, and all other ACs available out there.

What does the number mean?

Answer 1

AC600 has a transmission speed of up to 433Mbps and AC1200 has a transmission speed up to 1200Mbps. AC1200 is essentially faster.

Going with an "AC", "N" style wireless card does not mean you will be getting those speeds to your computer when browsing the web. You will still be limited by the maximum speed that your Internet Service Provider has allocated for you per your speed package. Going with an "N" or "AC" type card means you can transfer files within your local network at those speeds. Going with a type "N" or "AC" wireless card will increase the distance and speed of your local network because of its stronger transmission.

Answer 2

For client cards, those AC designations represent the rounded-up sum of the maximum signaling rates (PHY rates) that the card is capable of in each band.

So a typical first generation 802.11ac-capable laptop card could do the 1300 megabit/sec AC signaling rate in 5GHz (MCS 9, 3 spatial streams, 80MHz-wide channels). But since AC is 5GHz only, those cards all needed to also support b/g/n in 2.4GHz so they could connect to older APs. So they typically supported the 450 megabit/sec N rate in 2.4GHz (MCS 23, 3 spatial streams, 40MHz-wide channels). So you add up 1300 + 450 and get "AC1750". Even though 450 of that didn't come from AC at all! And even though the client couldn't use both bands at the same time, so it would max out at the 1300 megabit/sec signaling rate. And even when it gets the 1300 rate it would have actual throughput of only one-half to three-quarters of that signaling rate, due to 802.11 protocol overhead.

AC600 means 433 megabit/sec 802.11ac in 5GHz (MCS 9, 1 spatial stream, 80MHz-wide channels), plus 150 megabit/sec 802.11n in 2.4GHz (MCS 7, 1 spatial stream, 40MHz-wide channels). That adds up to 583, and they round it up to 600.

[P.S. My apologies if you saw an earlier version of this Answer. I had read the question too fast and thought it was about APs, not client cards. I deleted it temporarily so I could rework it to be a client answer.]