Timothy Parker Consulting Incorporated

Questions and Answers, Part 17

Q: I was reading an article about the war in Afghanistan and it mentioned steganography and computers. What is steganography and how does it relate to the computer business?

A: Steganography is actually Greek for “hidden writing” (as near as my rusty Greek can translate). What it means in general terms is hiding something important in something else, usually innocuous. Traditionally before computers this meant hiding messages in text such as newspaper or magazine articles and similar media. With the advent of computers, the art has gone very hi-tech.  Early computer uses for steganography was hiding messages in computer files (including binaries) that could be deciphered by reading the byte stream.  Now, it can mean such things as hiding photos or text in sound files, photographs, or video.  For example, a message can be encoded into the byte stream of a digital photo and placed on a Web site. Someone else downloads the photo, runs it through a filter that extracts and message, and there it is.  The hidden messages are usually impossible to see visibly with the naked eye because they are combined with other bits in the image or sound file, but don’t affect the host.  Relating to the conflict in Afghanistan, it seems that terrorist groups have been hiding instructions inside Web page contents, ready for download by any operatives who need them.  For this reason, intelligence organizations in many countries are running complex applications against Web site contents, looking for anything hidden or suspicious.  According to the NSA, the terrorist’s favorite Web site for hiding messages are pornographic (somewhat ironic considering the restrictions on this kind of material for the followers).

Q: Simple question: I keep seeing references to 1U, 2U and 4U for computers.  What is this?

A: They refer to the amount of space taken up in a component rack.  Racks are a standardized width (19 inches), and have holes drilled in mounting rails running up the front (and sometimes the back) of the rack case.  The holes are at regular intervals.  The rating you refer to indicates how many standard units of vertical rack space are taken up by the item bolted into the rack. A 2U component takes up twice as much space vertically as a 1U unit.  This becomes important as racks fill up, and you need to figure out what you can fit in a rack.  The trend in the business is to slim-line 1U components, which are a little over an inch tall. In most component racks, you can fit 42 Us total. 

Q: I know Linux is widely used on PCs but is it available for anything bigger?

A: Yup.  Linux has been ported to minicomputers and mainframes.  Serena Software (Burlingame, CA) offers a mainframe Linux for IBM S/390 and zSeries computers, for example. Why bother with Linux on a larger computer?  Primarily for two reasons: porting existing PC applications to a larger system without rewriting, and for migrating existing UNIX applications to a mainframe.

Q: What’s the difference between RDRAM and SDRAM?  I’ve seen both mentioned in Intel Pentium 4 systems.

A: The Pentium 4 was supposed to use a technology called Rambus, and the RAM chips that powered it were RDRAM (Rambus Dynamic RAM). RDRAM turned out to be faster than other types of RAM available at the time, and was supposed to help P4 systems turn in blazing speeds.  As usually happens, RDRAM was so expensive most people didn’t bother with it, and the older SDRAM (Synchronous Dynamic RAM) improved in speed enough to handle the P4’s demands.  Since SDRAM is a fraction of the price of RDRAM, Intel started providing a chipset (called the 845) to allow SDRAM to be used with P4 machines.

Q: What is an anonymizer?  Do I need one?

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Last modified: January 23, 2007