Using "the" and "a" when needed

In other words, when is a definite article ("the") required, when is an indefinite one ("a" or "an") needed, and when should there be no article at all? Again, the rules about this usage differ from other languages.

Definite Article Usage

"The" must be used every time the noun is defined by a complement, a genitive, an adjective, or another qualifier which is placed before the qualified noun. In the following examples, the qualifier that dictates this usage is italicized:

The SAP package has been augmented with new functionality is its latest version
The Windows version has different capabilities from the Unix version
The STARTUP.BAT file must be edited to change the default path
The primary index is a multiple of the actual sampling rate
The above function

However, a number or code, designating a specific instance of an object, will usually be placed after the noun it qualifies, and therefore the definite article will not be used in such cases:

We are releasing version 7.208 containing new files ABC.c and ABC.h [not "the version 7.208"]
This configuration requires performing action number one on file JPT.bin [NOT "the action number one"]
If the data file is of type A... [NOT "of the type A"]

In some cases, the qualifier may be equally acceptable before or after the noun, but the presence or absence of the adjective will still depend on the position of the qualifier. For instance, both these statements are well-formed:

The LTRANS directory contains the required files
Directory LTRANS contains the required files

The definite article appears in the first case only (before "directory") because the name of the directory, which qualifies it, appears before it. Both other possibilities ("LTRANS directory" or "the directory LTRANS") would be considered incorrect, or at minimum awkward.

Indefinite Article Usage

"A" or "an" indicates indefiniteness, but only in the sense of "one particular but unspecified instance of this type of thing," not in the sense of "the concept of this class of objects." The latter meaning is indicated in English by the absence of an article, or by the plural, but not by the indefinite article as is usually the case in romance languages. Examples:

"Software is easier to change than hardware" -- we're talking about software and hardware in general, the class of objects, not any particular piece of software or hardware.
"This method leads to faster programming" -- not "a faster programming"
"One can acquire new knowledge by..." -- not "a new knowledge"; but note that you would say "a new skill," because it is one particular but unspecified instance of the class "skills."
"A customer called in your absence, but I forgot to ask her name" -- it was a specific customer who called, obviously, not the general notion of customer! But "customers tend to call first thing in the morning to report problems" -- in this case, this is a generalization, we're not referring to a particular unnamed customer.

When you're not referring to a particular instance, when should you use no article, vs. using the plural? The plural can only be applied to things you can count (e.g., customers, skills). In the earlier examples, "software," "programming" and "knowledge" are not countable objects, so you leave them in the singular and omit the article.