Analogous to directories of files
- VHDL libraries contain analyzed (i.e. compiled) VHDL entities, architectures, and packages
Facilitate administration of configuration and revision control
- E.g. libraries of previous designs
Libraries accessed via an assigned logical name
- Current design unit is compiled into the Work library
- Both Work and STD libraries are always available
- Many other libraries usually supplied by VHDL simulator vendor
- E.g. proprietary libraries and IEEE standard libraries
Increasingly complex VLSI technology requires configuration and revision control management. Additionally, efficient design calls for reuse of components when applicable and revision of library components when necessary.
VHDL uses a library system to maintain designs for modification and shared use. VHDL refers to a library by an assigned logical name; the host operating system must translate this logical name into a real directory name and locate it. The current design unit is compiled into the Work library by default; Work is implicitly available to the user with no need to declare it. Similarly, the predefined library STD does not need to be declared before its packages can be accessed via use clauses. The STD library contains the VHDL predefined language environment, including the package STANDARD which contains a set of basic data types and functions and the package TEXTIO which contains some text handling procedures.