Alongside a wide variety of expensive, up-market products, two reasonably powerful C compilers for microcontrollers have emerged in the freeware circuit.The use of ‘free’ C compilers often presents unexpected problems because of the frequent lack of a user-friendly user interface. Also, despite their unrivalled price/performance ratio, these programs deter many potential users because their configuration and setup is not without problems. This article aims at providing some information to help overcome such initial problems. Specifically, we hope to supply some practical guidance in relation to the ‘SDCC’ compiler for the MCS-51 series and ‘AVRGCC’ for Atmel micros.