Monolithic system can have different meanings in the contexts of computer software and hardware.
A software system is called "monolithic" if it has a monolithic architecture, in which functionally distinguishable aspects (for example data input and output, data processing, error handling, and the user interface), are not architecturally separate components but are all interwoven.
Mainframe computers used a monolithic architecture with considerable success. Monolithic architectures implemented on DOS and earlier Windows based PCs often worked poorly with multiple users. This performance degradation is mainly due to poor mechanisms for record locking and file handling across local area networks.
An electronic hardware system, such as a multi-core processor, is called "monolithic" if its components are integrated together in a single integrated circuit. Note that such a system may consist of architecturally separate components – in a multi-core system, each core forms a separate component – as long as they are realized on a single die.