On Tue, 20 May 2008, andrew holway wrote:
Definitions please.
"Capacity" is usually used to refer to ability to hold a quantity of something. In the context of computing the something is usually "data". It can, and usually does, refer to disk, but with suitable modifiers it can refer to other capacities, e.g. RAM capacity (quantity of RAM). The term "can" be used to describe rates as well (in good English). For example the "capacity" of my ethernet connection is around 10 megabytes per second. The mental picture is of a wire holding a quantity of 10 megabytes of data (the capacity part) being delivered every second. No ambiguity, everybody understands. Similarly other rates like "compute capacity" in MFLOPs or the like are permitted usage and with suitable modifiers or context are well-understood, even though using the term with rates stretches the literal meaning of the word to where it is synonymous with "capability". Which it is, in ordinary English. I have the capacity to do good means that I am capable of doing good. Again, the conveyed picture is different; hence one would use the two sentence fragments in different contexts. Capacity means that I contain within me mental room to hold good impulses and a good nature, and one would actually often use the sentence to imply that while I do have the room and may have the impulses, I don't do it as often as the speaker would like. Capable just means that I can do good "Capabilities", then, are just abilities. In computing, they are pretty much any of the rates and capacities that describe a system, AND are a listing of particular things a system can do. My system is capable of running a Monte Carlo simulation on a lattice up to 100x100x100 in size, but I don't think it is capable of running one 1000x1000x1000. This is because it hasn't the memory capacity to hold the entire lattice image, and if I run it in virtual memory using swap, it would take the rest of my life to complete. My system and network are capable of serving a dozen slave systems in a parallel calculation at home. This means that they have the capacity to do this, of course, but if I said that you'd be visualizing it slightly differently. Hope this helps. The above is more or less according to the dictionary definition of capacity as a "stationary" or "passive" capability, which is why using it to describe a rate is second order in time; the stationary capacity of a line to transmit data PER SECOND. Capability is a bit broader and includes rates. rgb
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