cement v. concrete

Concrete is a building material containing an aggregate of sand, gravel, and crushed stone bound together by cement, which accounts for about 10% of concrete’s mass.

Cement is a powder made by heating a mixture of limestone, calcium, silicon, iron, aluminum, and other ingredients in a kiln, then grinding the resulting substance, clinker, with gypsum. When water is added to cement a chemical reaction known as hydration occurs, making the cement harden.

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Wikipedia on concrete

USB v. FireWire

• USB was designed as an inexpensive interface; FireWire (technically, the IEEE 1394 specification, also known as i.LINK on Sony products) was designed for high performance. This, and the predominance of USB in consumer devices, makes FireWire slightly more expensive to implement.
• FireWire 400 (IEEE 1394a) is rated at 400 Mbps. USB 2.0 is rated at 480 Mbps, but with more overhead, making their performance similar. FireWire 800 (1394b) is rated up to 3.2 Gbps. USB 3.0 (aka SuperSpeed USB) has a 4.8 Gbps transfer mode, but such devices won’t be readily available until sometime in 2010.
• USB is rated at 5 volts, and up to 2.5 watts; FireWire can handle substantially more power, at 30 volts and 60 watts. Devices that use a 6 pin FireWire connection usually use that one cable for both data and power.
• FireWire uses a peer-to-peer interface, which means that you can connect two cameras and copy digital video without the need for a computer, or you can allow multiple computers to share a peripheral. USB is a host-based topology, so devices must be connected to a computer.
• FireWire can be used for isochronous (meaning real-time) transfer of video, whereas USB connections aren’t guaranteed a sustained, uninterrupted data transfer.
• A USB host can support up to 127 connected devices; a FireWire network can contain up to 63 devices.
• USB 2.0 cables can be up to 5 meters long. FireWire 400 cables top out at 4.5 meters. However, FireWire 800 cables will work at distances up to 100 meters.
• The USB logo looks like an abstract tree; the FireWire logo resembles a flux capacitor. 

How Stuff Works on USB v. FireWire

Wikipedia on USB v. FireWire

MaximumPC on USB 3.0