IBM 5155 - Inside Mine
Below is a photo of the inside of my IBM 5155.
So that you can see the cards, I removed the metal shield that normally covers the right half (right, as viewed from the front of the machine).
SLOT 1: IBM CGA card
SLOT 2: AST SixPakPlus (extra RAM, RTC, serial port, parallel port, game port) (added to machine after purchase)
SLOT 3: IBM 5.25" diskette drive adapter
SLOT 6: DTC 5150X hard disk controller (added to machine after purchase)
SLOT 8: (slot 8 is not usable for many cards - see here)