Editing IBM PCjr (section)

=== Expansion ===
[[File:PCjr.twinSCSI.jpg|thumb|A PCjr featuring most upgrades available from PC Enterprises, including combo cartridge, dual floppies, twin ST-225 HDDs (bootable via [[Future Domain]] firmware hidden under cover on right). Replacement keyboard sits on top of the Taxan RGB monitor. System is showing "Battlechess".]]
The back of the machine does not have any expansion slots. Instead, several permanently mounted, proprietary connectors provide attachment to many built-in hardware capabilities, which replaced many of the features that PC expansion cards provided, including:

* Graphics hardware
* Multichannel sound
* Joystick ports
* Lightpen interface
* Serial port
* Cassette interface

Internally the PCjr did have expansion slots to support specific upgrades: a RAM upgrade, a modem, and a floppy drive.

On the right side of the machine, the system bus was exposed for use with "sidecars," upgrade modules which attached to the side of the machine. Third-party manufacturers produced a number of expansion units for the PCjr.<ref>{{Cite web|title=IBM PCjr Options and Accessories|url=https://www.brutman.com/PCjr/pcjr_options.html|access-date=2020-10-04|website=www.brutman.com}}</ref>