IBM 5160 - Slot 8
Slot 8 is different to the other slots.
From IBM's March 1986 edition of the 5155/5160 Technical Reference:
Page 1-3: "Slot J8 is slightly different from the others in that any card placed in it is expected to respond with a 'card selected' signal whenever the card is selected."
Page 1-16: "Timing requirements on slot J8 are much stricter than those on slots J1 through J7."
Cards placed in slot 8 must be slot 8 compatible in order to guarantee proper operation. Some cards will not work at all.
Some user manuals for particular cards indicate that the card is not compatible with slot 8. An example is the EGA Wonder 800+ card
In the EGA Wonder 800+ manual is, "... install the EGAWONDER8OO+ into any available slot except slot 8 in an IBM XT."
Cards that are slot 8 compatible usually have a 'slot 8' jumper, fitted when the card is in slot 8, and removed when the card is in a different slot.
Example slot 8 compatible cards
1. IBM Asynchronous Communications Adapter
Jumper: J13
See IBM Asynchronous Communications Adapter
2. Video-7 Enhanced Graphics Adapter (VEGA)
Jumper: P1
Described on pages 48 and 52 of the card's user manual
3. Microsoft InPort
Jumper: J2
This is a card for Microsoft bus mice.
Photo here
What is the purpose of slot 8 ?
I used to think that slot 8 was a special slot created for the 'extender card', a card required to connect an IBM 5161 expansion unit to the IBM 5160. However, one piece of evidence that it is not, is on page XVIII of the March 1986 edition of the 5155/5160 Technical Reference. That page is for the IBM 5155 (IBM Portable Computer), a computer that contains a 5160 motherboard, and shows the extender card in slot 2. There is evidence elsewhere. For example, the extender card is compatible with the IBM 5150 (later models), a machine that does not have an equivalent of the 5160's slot 8.
So, what then is the purpose of slot 8 ?
Sergey on the VCF wrote, "Not sure why J8 was designed this way. One of the possibilities is to use it for adding "system" devices that will use 0h - 0FFh I/O addresses."