http://www.bluetooth.com/Mobile computing used to be exclusively a matter of dragging a laptop computer around,* plus various adapters and other widgets. "Road warriors" have more choices now. Sometimes the computer is mobile, be it a laptop, tablet PC, handheld, or smartphone. Sometimes it's just the data files that are mobile, on various storage media. Or maybe only the user moves around, and the data files are parked on the network.
USB thumb drives, also called USB flash drives, are probably a benchmark technology for mobile computing these days; before you think about other methods, check if you can do it cheaper and easier with a thumb drive, perhaps combined with use of PCs at public libraries or Fedex Kinko's stores. Prices for USB thumb drives have been dropping; I saw 512MB for less than US$20 in October 2006, and 2GB at about the same price in December 2007.
For information about cell phone technology including smartphones (the convergence of PDAs and cell phones) see my Cell phone links page under Miscellaneous topics.
Damn Small Linux is a mini Linux distribution, designed to fit on and boot from a 50MB business-card format installable LiveCD. DSL can also use USB flash-memory thumb drives, either to boot from, BIOS permitting, or just to store configuration and data files on when booting from the LiveCD. In theory, if you have reboot privileges, you can carry your own OS and data files in your pocket, and summon them up on whatever hardware you encounter, without affecting the native installed OS and data at all.
You probably won't be able to boot DSL on library or rental computers, or any other Linux LiveCD, for that matter. In a corporate environment, their security setup might not actually prevent you, but there might still be a red-alert security freakout, immediately or later. In fact, lots of very competent Windows users are going to find this concept scary, even if you are a good friend. It's natural for people to be afraid of stuff they don't understand.
Maybe a better way to do mobile computing with DSL is to use it to resurrect an older notebook computer. DSL can run installed on some fairly old hardware, down to Pentium I with 32MB RAM. You can often get such machines cheaply or free, because relative to current Windows versions, people will tend to consider them useless.
In Chapter 12 of The Official Damn Small Linux Book, John Andrews describes installing DSL on an old Vaio notebook with no optical drive, which required him to take the notebook apart and temporarily connect its hard drive to a desktop computer, in order to do the DSL install. One could also simply buy or borrow an external CDROM drive; a USB peer-to-peer cable/adapter connection from the notebook to a PC with a CD drive might work; or there are adapter cables now to connect an IDE or SATA drive externally via a USB port. Of course any of those setups may only have drivers for Windows/Mac.
Conventional wisdom says that one can now do anything on a laptop/notebook computer that can be done with a desktop PC. In TV and movies these days, everyone seems to have a slim notebook and wireless Internet. I've been dubious about this style of computing, at least for ordinary folks not rolling in money. If your only computer is a notebook, which you carry around lots, what happens if it develops a hardware problem? You have no computer? With a generic desktop PC, if something like a power supply quits, you just need to replace that piece.
If you use a cheaply-acquired older notebook with DSL installed for mobile stuff, and it quits, you can just say "easy come, easy go," take it to the local computer recycler, and scrounge yourself another one. Also, since your mobile computer is not expected to do everything in this model—requiring it to have every port type known to Man—it can be a light and handy notebook with a slim form factor.
http://www.bluetooth.com/PCs have ports, connections for peripherals such as a printer or an external modem, that allow data to flow both ways. Early PCs had serial and parallel ports, port types which existed before PCs did, and you connected your printer to the parallel port and your external modem to a serial port.
People also sometimes want to temporarily connect two PCs directly to each other to transfer data. There were early-days methods for doing that using the serial and parallel ports, notably the product LapLink and the DOS and Windows utilities INTERLNK and Direct Cable Connect.
Conventional serial ports at 230 Kbps are still acceptable for connecting external V.90 modems, because the data transfer rate is limited by the 56 Kbps speed of the modem-to-modem connection. We have other gadgets now that would like to go a lot faster.
There are two newer types of high-speed ports commonly seen: USB and FireWire (IEEE 1394). Both port types are used to connect fast peripherals and sometimes to temporarily connect two PCs. Early USB 1.0/1.1 ports had data rates of 1.5-12 Mbps and were already faster than serial and parallel ports. Common USB ports now support USB 2.0; USB 1.1 ports are only seen on older hardware.
Nominal transfer rates: USB 2.0 480 Mbps, FireWire 400 Mbps. It would appear at first glance that USB 2.0 is a little faster, but there are architecture differences to be aware of.
USB is a host-based or master/slave protocol: one end of a USB connection is always the boss. USB connections that need to behave like peer-to-peer, such as cables for directly connecting two PCs, require a little adapter circuitry.
FireWire is fundamentally a peer-to-peer protocol, and the devices on the ends of a FireWire link can negotiate data handling. In practice FireWire400 will be faster than USB 2.0, especially for sustained throughput such as with an external hard disk.
There's also a new 800-Mbps version of FireWire on the way, sometimes referred to as FireWire800 or IEEE 1394b, and the FireWire spec provides for up to 1600 Mbps.
One advantage USB retains is that nearly every Windows PC you encounter will already have USB 2.0 ports, as shipped from the manufacturer, often including front-panel ports. FireWire ports are mostly seen on digital camcorders, Apple Macs and iPods, Sony PCs, some PCs designed specifically for audio/video production, and as aftermarket add-ons to other PCs. A USB connection also always supplies power as well as data, which some FireWire connection types don't.* There are a few peripherals around designed to use both a FireWire and a USB connection, in which USB is only supplying power.
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