K56flex 'upgrade' may make your modem run slower than before

K56flex 'upgrade' may make your modem run slower than before


K56flex modems based on a chipset by Rockwell Semiconductor may give you slower, not faster, speeds if you upgrade to the new V.90 international communications standard.

K56flex modems, which theoretically can download 56Kbps on good phone lines, have been touted as "software-upgradeable" since they first appeared in 1997.

But you may not want to immediately upgrade the firmware in the K56flex modems that you run. That's because most K56flex modems currently in use lose their downward compatibility with the K56flex protocol when the firmware is upgraded to V.90.

This situation has several side effects:l If you've been connecting to an Internet service provider using K56flex - and you upgrade to V.90 but your ISP does not - your download speed will immediately drop back to the old V.34 standard, meaning 28.8Kbps or 33.6Kbps.l If your ISP does upgrade to V.90 and you want to do the same, you'll need to find and run a specific flavour of the upgrade for your brand of modem - there is no universal upgrade that will work.l To make matters worse, some of the early K56flex modems had their code built into ROM, meaning they aren't software- upgradeable at all. You'll need to make a ROM chip swap.

This mess exists because the original Rockwell chipset for K56flex modems - produced in a furious attempt to catch up to the x2 brand of 56Kbps modems introduced by US Robotics - can address only 1MB of memory.

That isn't enough to hold both the new V.90 code and the old K56flex code, plus all the other basic functions that a modern desktop modem supports.

Dean Grumlose, a product line manager at Rockwell in the US, says both K56flex and V.90 code can fit into server-side ISP and corporate digital modems with 1MB of memory, but not into client-side desktop modems. The code to implement this in most server-side environments, however, is still in beta testing and is not yet widely used.

Upgrade immediately

I wrote last week about a controversial test Boardwatch magazine ran in its March issue lauding x2 over K56flex modems. Boardwatch says only 40 per cent of Internet users connect through their company LAN, and the other 60 per cent connect from home using modems, so modem speed isn't merely academic.

The upgrade decision for x2 modems is straightforward - I recommend you upgrade immediately. All x2 modems were shipped with 2MB of memory to make them both software-upgradeable and downward compatible, says John Powell, an engineer in 3Com's US Robotics unit. You can get the x2/V.90 upgrade from for client-side modems. The server-side software for ISPs is already installed in many places. Even if your ISP hasn't upgraded from x2 to V.90 yet, your upgraded modem will still work at high x2 speeds. And you may gain a 7 to 10 per cent performance improvement due to better error handling in the new x2/V.90 code, Powell says. (Don't expect much more than 45Kbps downloads from any of these modems, despite the implication of "56Kbps".)This kind of easy upgrade isn't the case with Rockwell's K56flex.

"What Rockwell has done is allow each vendor to decide what to do," said Lisa Pelgrim, a senior analyst at Dataquest. That means dozens of different modem vendors have shipped a zoo of non-upgradeable, partially upgradable, or "dual-mode" (2MB) K56flex modems, each with its own upgrade software. (K56flex modems based on the Lucent chipset seem to have sufficient memory for downward compatibility.)Owners of K56flex modems don't get much speed benefit from going to V.90. So if you're happily connected to an ISP with a K56flex port, you may as well not change.

But you can find upgrades for your particular modem at, which tracks the status of a wide variety of modems.

Brian Livingston is the co-author of several best selling Windows books, including the most recent Windows 95 Secrets (IDG Books). Send tips to He regrets that he cannot answer individual questions.

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