Technical information

CHAPTER 1
Introduction
How the DOS Compatibility Card Works 5
Figure 1-3 Simplified block diagram of the DOS Compatibility Card
The diagram shows some of the hardware devices on the processor card: the memory
controller and DRAM SIMM, and the VGA controller and video RAM. It also shows the
Pretzel Logic IC, which acts as a bus converter between the processor card and the
Macintosh computer and provides the interface to Macintosh devices that emulate PC
devices. Logic devices on the PDS adapter card translate the PDS control signals from
the Macintosh computer and demultiplex its 64-bit data bus down to a 32-bit bus for the
80486. Chapter 2, “Hardware Design,” gives more information about the devices on the
DOS Compatibility Card and the way they operate in conjunction with the Macintosh
host computer.
Note
The processor card in the DOS Compatibility Card assembly
is functionally similar to the 80486 card used in the earlier
Macintosh Quadra 610 DOS Compatible computer.
◆
CPU

80486DX2
DRAM SIMM
DOS Compatibility Card
Power Macintosh 6100
Memory
and bus
controllers
AT bus
Keyboard Floppy disk SCSI hard disk Serial ports Ethernet port
PDS
Video
DRAM
VGA
controller
PDS
adapter
Keyboard
controller
I/O controller
Curio
I/O
interface
Video and
memory
controller
CPU

PPC 601
Pretzel
Logic IC
Video
DRAM