Expressively, IMP is highly similar to ALGOL and includes all the ALGOL-style block structure, reserved words (keywords), and data types such as arrays, and records.
IMP provides significant control over the storage mapping of data, plus commands for addressing within parts of words.
Most IMP compilers offer compiler-generated runtime checks and a stack trace (backtrace) facility by default, even in production code.
The ERCC Implementation of IMP for the ICL System 4 (known as IMP9) offered a syntax-driven macro facility (designed by Alan Freeman) that was similar to the Compiler Compiler features offered by IMP's predecessor, Atlas Autocode.
The diverged IMP and IMP77 were later consolidated into one language with the introduction of the IMP80 standard, supported by implementations from the Edinburgh Regional Computer Centre.