Great Hierophant
Veteran Member
In the BIOS of the IBM PC and XT, the following were supported:
3xParallel Ports
4xSerial Ports
1xGame Port
1xMonochrome Adapter
1xColor Adapter
2xInternal 360KB drives (720KB supported in later XTs)
2xExternal 360KB drives
640KB of RAM
8087 Math Co-processor
83-Key Keyboard (101-Key LEDless Keyboard for later XTs)
5 (PC) or 8 (XT) 8-bit ISA slots
Cassette Port (PC only)
Of course, the problem was that there weren't enough resources in a PC or XT to support all these options, nevermind additional devices like a hard drive.
Each printer port came on a separate card, as did the game port and the serial port. One printer port is given by the MDA card. Only with an Expansion Chassis could you possibly completely fill out a PC using contemporaneous IBM Hardware.
Color/Graphics Adapter
Diskette Drive Adapter
Printer Adapter
Game Control Adapter
Expansion Card
Asychronous Communications Adapter
Asychronous Communications Adapter
Asychronous Communications Adapter
Asychronous Communications Adapter
Monochrome Display and Printer Adapter
384-512KB RAM Card
Printer Adapter
Expansion Card
Without considering a Fixed Disk Drive Adapter (technically not supported in PC or XT BIOS), IRQs seem to be a major problem. Only 3-5,7 are available in an 8-bit system. I believe that all the Printer Adapters would use IRQ7 and one pair of Asych Adapters should use IRQ 4 and the other pair IRQ3. It is interesting to note that if you use a Color/Graphics Adapter, the system will only support two parallel cards. However, never use COM1/COM2 at the same time as COM3/COM4 and never use any two LPTs at the same time
If you add a Fixed Disk Adapter (which would require an XT), it will take IRQ 5 and you can only add one (IBM brand) as the I/O ports of two would overlap (as would a second IBM Diskette Drive Adapter.)
3xParallel Ports
4xSerial Ports
1xGame Port
1xMonochrome Adapter
1xColor Adapter
2xInternal 360KB drives (720KB supported in later XTs)
2xExternal 360KB drives
640KB of RAM
8087 Math Co-processor
83-Key Keyboard (101-Key LEDless Keyboard for later XTs)
5 (PC) or 8 (XT) 8-bit ISA slots
Cassette Port (PC only)
Of course, the problem was that there weren't enough resources in a PC or XT to support all these options, nevermind additional devices like a hard drive.
Each printer port came on a separate card, as did the game port and the serial port. One printer port is given by the MDA card. Only with an Expansion Chassis could you possibly completely fill out a PC using contemporaneous IBM Hardware.
Color/Graphics Adapter
Diskette Drive Adapter
Printer Adapter
Game Control Adapter
Expansion Card
Asychronous Communications Adapter
Asychronous Communications Adapter
Asychronous Communications Adapter
Asychronous Communications Adapter
Monochrome Display and Printer Adapter
384-512KB RAM Card
Printer Adapter
Expansion Card
Without considering a Fixed Disk Drive Adapter (technically not supported in PC or XT BIOS), IRQs seem to be a major problem. Only 3-5,7 are available in an 8-bit system. I believe that all the Printer Adapters would use IRQ7 and one pair of Asych Adapters should use IRQ 4 and the other pair IRQ3. It is interesting to note that if you use a Color/Graphics Adapter, the system will only support two parallel cards. However, never use COM1/COM2 at the same time as COM3/COM4 and never use any two LPTs at the same time
If you add a Fixed Disk Adapter (which would require an XT), it will take IRQ 5 and you can only add one (IBM brand) as the I/O ports of two would overlap (as would a second IBM Diskette Drive Adapter.)