I always recommend to avoid rounded and over-long cables.
See the unterminated ribbons that we are familar with are very fragile standard and suseptable not only to out side interference but to their own crosstalk interference.
You remember that when electricity travels thru a wire it creates a magnetic feild. Magnetics and electricity go hand in hand.
When you have a very stong magnetic feild passing thru a wire what happens? You create electrical current in that wire. Just like a radio intenna picks up radio waves and they naturally turns into electrical feed into the back of your radio. Remember crystal radio sets that turn radio waves into electicity and then sound waves with no external power source other then the radio waves?
Old 40 wire IDE cables are not capable of the higher speed data transfers that today's harddrives demand. After all that stuff (Parrellel ribbons) was created back before the 8086 days, it was fast enough then it's not good enough now. They don't work because the high frequencies passing thru those wires creates interference and the crosstalk f**ks up the signals.
So they created the 80 wire standard. Those extra 40 wires DO NOT carry any data signals. They are grounded. They sit in between data wires so that they keep them seperated.
Their sole purpose is to absorbe the excess energy from the signals generated by the neighboring wires and transmit this to ground.
Now when you rip appart all these wires and begin to criss cross them or to smoosh them together into a rounded cable all the signals and excess energy begin to go from wire to wire, creating distortion and screwing everything up.
SCSI wires can be much longer then IDE stuff because they transmite stuff differently and are terminated. Take the terminators off or hook up older non-self-terminating equipment and good luck trying to make it work properly.
The same thing happens when you take thin speaker wire and rap it up or cram it with a bunch of electrical wires. Ever notice how some people's stereos have a loud and annoying hiss when their is nothing on them and they are just sitting there? Ether caused by crappy stereo equipment or interference with the speaker wire themselves.
Be sure that engineers worked long and hard figuring all this stuff out. When they say the wire's maximum length is 18 inches you can be sure that they know what they are talking about. They are interested in making reliable and robust equipment, not selling you expensive and semi-useless cabling.
Most people how have over-long cables and rounded cables say that they work fine, because as long as they know they are working fine. They just probably spent a couple hours modifing cable or spent 30 dollars on wires that you otherwise get free with you harddrives or motherboards.
The data corruption is very subtle, there is nothing on your computer (especially if you run windows) that's going to give you any indication that something is going wrong. Plus today's hardware manufacturers are very good about making very good hardware.(compared to just a few years ago) Their chipsets they using in motherboards and harddrives can translate and handle dirty signals and malformed stuff very well and still extract good data from it. Plus there is a element of data correction built into the devices.
For instance if you are transmitting a signal 1010, but it gets 1011 it knows something is wrong and tells the other device to retranmit. But it's very limited, I am not completely sure of the details, but if you send a signal 1010 and it gets 0101 it may not be able to tell the difference and thinks it'd good data.
So hardware nowadays can handle bad data and correct it but only up to a limit.
For instance I read a review of long rounded cables were they hooked it up and it worked fine. They did benchmarks and only saw a very slight drop in file performance from a in-spec cable and a out of spec rounded cable. So it seemed to be fine and they recommended the rounded cable due to it's easier routing in the case and cooler looks for modders.
However they never explained exactly why there was any drop in performance at all! The drop in performance was more then likely due to the error correction built into the hardware being used over and over again to correct bad transmissions, and having to retransmit data. This didn't make much of a difference in the short term, because the standard can handle 1 error at a time just fine, but 2 errors in a row it can't handle. This a cumilative effect.
You programs will run fine, your OS will be stable. Your files will be good for a long time. But over a years time, or 2 years time things will begin to randomly mess up in small ways, then in bigger ways.
However most people are used to it and chalk it up to windows crapping out and simply reinstall. Which may be true under normal circumstances. But other software and OSes don't have the gradual decline and may start messing up themselves.
If you realy want them, go ahead. They will probably work, but if you start having issues with corrupted files or screwed up OSes and programs, you know one place to start making changes to fix the issues.
PS Go look into the Apple Power G4's and G5 (not that Apple is uber-god-like-computer-maker, but it's just a different mentality then PC makers) cases and you'll quickly see how thru good case design that ribbon cables can take up much less space then rounded ones and how you can deal with the length issues in other ways.
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