channelZ.org
You can make backups, but if you can’t restore from them you’re just wasting your time. This clip, according to the Pixar employees who made it, is 99% true. An admin at Pixar ran RM* (a UNIX/Linux command to remove everything) on the wrong server—the one storing Toy Story 2. They thought, no problem, we’ll just restore from backups! When they attempted to do so they found the backups they had been making for the last month were corrupt. Which begs the question, how many “@” symbols are there in “Oh #@$%!!” The moral of the story is, perform a periodic test restoration of your backups, just to make sure you can. Even on my own home system I periodically do that. It may seem paranoid to some, but you aren’t being paranoid if they really are out to get you. And Mr. Murphy, armed with his infernal law, is out to get you … and your data.
Hat tip to Rob Huddleston for putting me onto the video.
If you’re interested in learning about Linux you should know about DistroWatch. They keep a Page Hit Ranking table on their homepage, which allows one to easily see which distributions are trending in the Linux community, and one can get a pretty complete thumbnail sketch of what a distribution is about with just one click. Download mirrors, related websites, screenshots & reviews are all posted on the information page for any distribution, so any thirst you might have for more information is easily slaked. DistroWatch is to Linux as IMDB is to movies. It’s good stuff, and a great resource.
Browsing DistroWatch makes me wish I had more free time to play around with these various distros. If you’ve got the bug and are ready to play, but would rather not screw around with (OK, screw up) your main PC, consider creating a virtual machine with something like VMWare Player or VirtualPC. Then install the distribution of your choice to that and you’re ready to explore a new OS.
Problems due to faulty RAM can be difficult to diagnose. If a system’s RAM has gone bad the user can experience program crashes, spontaneous reboots, sudden system freezes, BSODs (Blue Screens of Death), corrupt data, and more. The problem is those symptoms could also be caused by a bad CPU. Or a bad motherboard. Or glitchy power.
One classic method of diagnosing RAM problems is to replace the RAM and test to see if the symptoms disappear. But a tech should know which tools can make you sure. After all, no one wants to buy new RAM only to have their certified tech then tell them, “Oops, I guess maybe it was the CPU. Or the motherboard. Or … ” Hardware RAM testers exist, but are rare, and a tech would almost never have access to one in the field. Software RAM testers are less reliable, but are often free and easy to include on a removable drive as part of a software toolkit. That makes them a go-to tool when the symptoms suggest bad RAM. False negatives are common—bad RAM will often be reported as A-OK after a scan. But if your RAM tester tells you your RAM is bad you have a smoking gun clearly implicating the culprit.
Microsoft includes Windows Memory Diagnostic with Server 2008, Vista & Win 7. For other OSs, MemTest86 has long been the classic software tool for this job and it does the job well. A downside is that you must restart your computer, since neither tool can test your RAM while your operating system is using it. Thankfully, for those quick and dirty jobs, HCI Design has given us MemTest for Windows. It’s a Windows executable, so you just run the program and it starts testing away while Windows and maybe other apps are happily clicking away. If you think that MemTest for Windows can’t test RAM currently being used by other programs, you’re right. That may be a deal breaker for some, but MemTest for Windows will wait for currently used RAM to become available, and will test it when it does.
The end result is that the tech can be confident that if they run MemTest for Windows for x hours, then the system is capable of running for x hours without any RAM related problems. One might realize that one could simply run a computer for x hours without any testing software, and prove that the system could run for x hours. But remember, the diligent technician is looking for that smoking gun that leads them to the culprit. If MemTest for Windows does throw an error, the tech has closed the case with solid evidence. MemTest86 and MemTest for Windows are both freeware.
Preparing a hard drive for disposal can take the form of software which electronically randomizes the bits, or a device which magnetically erases the information. However, nothing beats the finality and satisfaction of physical destruction. A company called SSI Shredding Systems has produced a series of videos demonstrating their products, which include a hard drive shredder. For fun I recommend their videos of other items being shredded, even if they have nothing to do with data security. My favorite is the VW Hippie Bug. Other companies have used YouTube to demonstrate their wares, and their commercials can be instructive and interesting. On the flip side of the coin, a British program called The Gadget Show tested a couple of rugged storage systems by subjecting them to water, then explosives. The results were as entertaining as they were illustrative.
All A+ & Network+ certification books describe the difference between regular cable and plenum cable in a fire, but would you like to see the difference? L-com sells cable and put together a series of videos so that customers can see what they’re paying for when they spend extra for plenum rated cable.
I’m fond of pointing A+ & Network+ certification students towards HowStuffWorks’ Computer Channel. The full color illustrations are nice, but the real draw is the interactive Flash-based graphics that can show processes, not just hardware. Some of the nice ones I’ve found:
- Front-side buses
- DRAM
- Flip-flops (used in high-speed cache memory)
- Inkjet printers
- Routers
I’ve just posted a network speed table to help you memorize the speeds of all the various connections. CompTIA is fond of asking a question on the A+ & Network+ tests involving a scenario where a given minimum bandwith is listed, and you must know which connection would be fast enough to meet their criteria. Thus, I’ve listed all of the connections mentioned in most A+ & Network+ certification books, and sorted them by typical speed.
I consider the Network Speed Table a work in progress and I’ll be updating it in the future. Particularly, CompTIA mentions other network types such as satellite, cellular, and Bluetooth, which the table does not include. When I update the table I’ll post a notification here on the front page. Additionally, the speeds listed include minimum, maximum, and typical speeds. For this information I drew from various sources, including A+ certification books, books for other CompTIA certifications including Network+ and Security+, and good old Wikipedia. As such there is certainly room for some, shall we say, discussion about the speeds. The speeds I list as typical are particularly open to interpretation and may conflict with your personal experience, but rest assured those numbers were not pulled out of a hat. They were pulled out of Wikipedia. I know that’s not an authoritative source, but that way I know if you and I have a disagreement over them, then other geeks have already had the same disagreement and the result you see on the table is the result the Wikipedia-editing geek community has come to rest on (for now). However some of the other numbers were drawn straight from CompTIA A+ & Network+ certification books, and I’ve been around enough to know those numbers aren’t always accurate, even though they ought to be. Heck, sometimes two different books don’t agree with each other, even though they have each gone though a supposedly authoritative vetting process. Therefore, if you find an inaccuracy in the table, or have any suggested addition or edit, leave it in the comments!
I created a guide to the 7-layer OSI model to help students studying for their Network+ certification test. The OSI model is in the central column with descriptions of each layer. Since TCP/IP was designed using a 4-layer model, I’ve included the 4-layer TCP/IP stack in the leftmost column to illustrate how each of the 4 layers maps to the 7-layer OSI model. In the rightmost column I’ve created a guide mapping individual protocols to the appropriate layer. Protocols that are part of the same family are colored appropriately.
I used to get a lot of questions in class from students transitioning into the computer field asking what individual pieces of hardware look like. So I’ve made each piece of hardware a link that performs a Google Image search for that item.
There are a lot of visuals on the web illustrating the 7-layer OSI model, but this is the only one I’ve ever seen that maps the OSI model to the TCP/IP model, and includes all relevant (to Network+) protocols with port numbers and their relation to each other, and also includes hardware. I’ve formatted the guide as a table that is sized for printing on 8.5X11 paper, if that aids in study.
I started channelZ.org back in 2002 in order to have a repository for information in my classes that wasn’t in the book. Initially a student asked if I could provide a printed list of all the sites that I mentioned in class. I’m not a big fan of printed handouts, so I created the list and posted it online.
I’ve been meaning to migrate the old site to a blog format for sometime. I’m looking forward to the flexibility of tagging posts rather than forcing them into the rigid structure of site categories. Additions will be easier, & therefore more frequent. Students will be able to reach me more easily (currently folks have to spell Zahorowski correctly at least once in order to get email to my work address).
And if you’re wondering what I’m riffing on in the title of this post, here’s a hint:
