Borland Pascal's Standard Units
A unit is a collection of constants, data types, variables, procedures, and functions.
Borland Pascal provides the following standard units:
These standard units provide support for your Borland Pascal programs and are stored in TPW.TPL (Windows), TPP.TPL (DOS protected mode), or TURBO.TPL (DOS real mode).
Each unit is like a separate Pascal program: It can have a main body that is called before your program starts and does whatever initialization is necessary.