Difference between SB6120 and SB6121 Can anyone tell me if there are any major differences between these two items? Reading the spec sheets, all I can determine is that the SB6121 has a new case, an on / off switch, and a price increase. I've had problems with the SB6120 and Comcast in Denver, and would attempt the SB6121 if I knew the hardware/firmware was actually updated.
The box for the SB6120 was in print BEFORE Win 7 was released. Thats why it isn't mentioned. They arent updating the print. ( note the latest Mac OS, Lion, isn't listed either. ( kind of dumb since the modem doesnt even see the OS or care. Its upstream of the computer. It only cares about the Ethernet protocall it's serving (10/100/1000 base T)) Notice the new box for the SB6121 doesnt mention any Windows -or- Mac operating systems anymore. Motorola got smart and stopped printing OS versions on the box so they wont have to change the printing every time a new OS is released.
SB6121 was just listed today on Comcast's website. But still call your local Comcast provider BEFORE purchasing a modem because not all areas may be ready to provision them. The reason a MOCA filter is needed is that when using MOCA in your network, it may cause interference (and poor performance) in the cable modem, regardless of the frequencies used. The MOCA signal (which is quite high) can overload the cable modem tuners which can't reject the MOCA signals entirely without a filter.
and the only difference is a couple of asterisks got taken off some speed specs (with the 6120 the fastest broadband frequency was specced for fewer than all signalling protocols; that restriction is not mentioned with the 6121). And the on/off button. And the box. And the lights get pictograms on the 6121. All of the real differences are likely to internal parts; some better, some cheaper. Maybe a tweak for a big cableco's particular quirks (see re asterisks above). No mention of default firmware at all. There is also a blurb on the front page for the 6120 regarding using TFTP and SNMP for management that isn't there for the 6121. I doubt they actually deleted the capability on the 6121; more likely they wished they hadn't touted it on the 6120 for some reason.
As for the MoCA, you may not have problems, but random equipment hooked up to standardized wires means nonstandard effects and service calls to cable operators. Cable companies did not expect intrusions before. Their solution is not to ban you from fiddling with their metal but to reduce what they consider noise on their front end. Nice of them. Don't know if it's $10 worth of nice, but still nice.
The SB6121 has a MoCA (Multimedia over Cable Alliance) filter inside, the SB6120 does not. From what I gather MoCA can cause noise at the higher frequencies that DOCSIS runs on. So if you use MoCA devices in your house you may want the SB6121.
Note the Comcast cable modem page now notes 1 star for "Certification" for the SB6120 and 3 stars for the SB6121 (http://mydeviceinfo.comcast.net/). So it appears that the SB6120 has not undergone any "Physical and Environmental (P&E) evaluation" whereas the SB6121 has had full P&E testing.
The 6120 most certainly does work with Windows 7. I'm also using my 6120 in Denver as well. I've not had any issues using mine. The problem you may be having is that the DOCSIS 3.0 service may not be available in your area yet.
A downside here is the review posted for the 6121. It sounds like this modem is not provisioned on Comcast's network yet. So there's not a need to spend $100 for a plastic paperweight at the moment.
I've owned lots of cable modems and until recently had absolute faith in Motorola. Their SB 5100 is basically the gold standard. I've installed several for friends/family/clients and while I'm sure they do eventually go bad, the one's I've had are all 5+ years old and still going strong (2 are 10+ and work perfectly). I decided to give docsis 3.0 a try about 6 months ago and bought the 6120 here on amazon. It worked great at first and I saw low ping times, and fast speeds (Even faster than I was actually paying for). Very recently the modem blew out and I started to see ping times >250 ms (I'm regularly getting ~15ms). Motorola is sending me a new SB6121 because they are no longer manufacturing the 6120. A comcast rep told me that the 6120s are far from the gold standard the 5100 was. I always take things that comcast reps tell me with a grain of salt (I've found they are wrong a lot), but given that Motorola isn't making the 6120 anymore its not a stretch to think that they may suffer from some problems.
I'm sure this was true when you posted, but I just want to update the discussion that Comcast now lists the 6121 on their approved device list: http://customer.comcast.com/help-and-support/internet/list-of-approved-cable-modems/