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It was common to offer access to the internal bus through an expansion connector, or at least provide space for a connector to be soldered on. This was a low-cost option and offered the potential for expansion, even if it was rarely used. Typical expansions would be I/O devices or additional memory. It was unusual to add peripheral devices such as tape or disk storage, or a CRT display
Later, when [[#Single-chip microcontrollers|single-chip microcontroller]]s, such as the [[8048]], became available, the bus no longer needed to be exposed outside the package, as all necessary memory could be provided within the chip package. This generation of processors used a [[Harvard architecture]] with separate program and data buses, both internal to the chip. Many of these processors used a [[modified Harvard architecture]], where some write access was possible to the program data space, thus permitting in-circuit programming. None of these processors required, or supported, a Harvard bus across a single-board microcontroller. When they supported a bus for expansion of peripherals, a dedicated I/O bus, such as [[I²C]], [[1-
== External bus expansion ==
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