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Ask Dave
by Dave Hamilton

He from whom all Mac knowledge flows...




The Low Down On Ethernet And Data Recovery
February 11th, 2000

Good day, my friends! Today we explore and explain the mysteries behind Ethernet, cross-over cables and hubs. Then we talk about options for disk recovery software and finish up with a little correction from last time! There's lots of good stuff here today, folks, so don't miss a bit! If you have a question of your own, you can e-mail me or ask away in the Forums! Enjoy!

Lydia Stapatzi writes, "I have a Mac clone (UMAX C-600) and just installed an Asante 10/100 Ethernet card. My second machine is a PowerMac 9500. I tried to connect them together by using an RJ45 Ethernet cable and when I go to the AppleTalk control panel to select Ethernet, I get an error message telling me there are no connections and it will not stay on Ethernet. By the way, if everything works out fine I'm planning to purchase a hub to connect another Mac clone (UMAX S-900), Apple LaserWriter (4/600) and Epson 740 InkJet printer.

Ah, Lydia! If only you'd taken the plunge and bought the hub to start with, we wouldn't be having these problems. You see, Ethernet is a two-way protocol. With your 10Base-T connector, there are 4 wires used in the cable -- two for sending, and two for receiving. Every computer uses these pairs the same way, so there's no incompatibilities. So, if we take a normal, "straight-through" Ethernet cable and connect two computers together directly, we're going to have problems. The send wires on one computer will be connected to the send wires on the other. As would stand to reason, the receive wires would be the same way. If you've got receive going to receive and send going to send, the two computers will never hear what the other one is saying! Think about it like your telephone (and this is a loose interpretation because most phones echo your voice back to you in the earpiece... bear with me) -- when you talk into the phone's mouthpiece (the "send" connector on your end), your voice comes through the earpiece on the other end (the "receive" connector). If your voice came throng the other person's MOUTHpiece, they'd never be able to hear you. That's what's happening here... Thankfully, a hub is built to deal with this problem perfectly. The hub takes the send from each computer and connects it to the "receive" of all the other computers. That way your data gets sent out on the right channels, and you receive the data from other computers properly as well. So go get your hub, and you'll be good to go.

There is another way here, but it only works for a network of 2 computers. We discussed the "straight-through" cable above that connected send to send and receive to receive. There are such things as "cross-over" cables, that, as you might guess, switch that -- they connect send to receive and receive to send, in effect bypassing a hub. Of course, this only works between two computers, and as soon as you add a hub to the mix you'll need to use "straight-through" cables to make everything work properly. Another thing -- many Ethernet ports on Macs need to see power on the other end before they'll initialize properly. With a hub this isn't a problem -- the hub provides the necessary "response" when the computer powers up, and things work fine. However, with two Macs and a cross-over cable, you'll often need to "reset" the Ethernet connection if you start one computer before the other. It can be a real pain and a hub makes it *much* easier.

Bill Culpepper writes, "What are my options for trying to recover data files no longer shown in the directory for an iBook running Mac OS 9? What utility software do you recommend and what version of the software do I need to make it work with Mac OS 9?"

Assuming that we're talking about files that have just "disappeared" as opposed to being manually deleted, there are a couple of options here. The first that comes to mind is Norton Utilities. It may be able to repair your directory tree and show the "missing" files. Let it do it's "backup" of your directory tree in case you want to undo your work! Another option that I've heard good things about is DiskWarrior. Again, it is built to repair directory damage that so often plagues users of most operating systems from time to time. Many readers have written in singing the praises of DiskWarrior. There's also MacMedic from the folks at Total Recall. They used to just service hard drives that were sent into their shop (and can recover almost ANYthing -- for a substantial cost). Now they've released a version of their software to the public that can help avoid the expense of sending your drive into them and having them take it apart for repair.

Unfortunately, none of these "after the fact" utilities is a replacement for a good backup. Depending on your needs, you may only need the shareware SimpleBackup (US$5 registration), or you might want to look into something more robust like Retrospect. Either way, you should *definitely* have something that you use to back up your data on a regular basis.

Update - Older Versions of Mac OS Still Available

Frederico writes, "In your column of Friday, February 4th, you told poor Marcia that she'd have to have OS 8.0 to get 8.1 or be forced all the way to OS 9. Lots of resellers, like SmallDog.com, have plenty of old-stock OS 8.0 and OS 8.1, as well as 8.5.x and 8.6 (full installers) on sale for cheap (and legal). You can get boxed versions with manual or CD-only. You can also get all of the same on eBay, should you feel trusting."

Thanks, Frederico. Poor Marcia! I feel as though I led her astray. A little searching reveals that this stuff is available at other places, in addition to Small Dog Electronics. MacWarehouse has the 8.5 installer available for purchase, as well.

That's it for today, folks! Thanks for all the great feedback and keep those questions coming to askdave@macobserver.com. Alternatively, you can head over to the Ask Dave! Forums and see what everyone has to say!

P.S. Have a Nice Day.

is President and CEO of The Mac Observer, Inc. He has worked in the computer industry as a consultant, trainer, network engineer, webmaster, and a programmer for most of the last 10 years. During that time he has worked on the Mac, all the various Windows flavors, Be, a few brands of Unix, and it is rumored he once saw an OS/2 machine in action. Before that he ran some of the earliest Bulletin Board systems, but most of the charges have since been dropped, and not even the FBI requests that he check in more than twice a year.

Ask Dave is here to answer all the Mac questions you have. Networking, system conflicts, hardware, you ask it, he can answer it. He is the person from whom all Mac knowledge flows....


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