Microsoft® Manual of Style, Fourth Edition

How to use acronyms and other abbreviations

First mention

In general, spell out acronyms on first mention, and include the acronym in parentheses immediately following the expanded form. On subsequent mention in the same topic or article, you can use the acronym without spelling it out. Exceptions to this guideline are indicated in the table. When you spell out the acronym, follow the capitalization given in the Expanded form column of the table unless noted otherwise.

Microsoft style

1-gigabyte (GB) hard disk

information stored in random access memory (RAM)

If the first mention appears in a title or heading, use your best judgment to determine how much information to include. For example, if space is limited, use the acronym without spelling it out. ...