Specifications

CHAPTER 2
Hardware Design
Hardware Features 15
Hardware Features 2
This section describes the microprocessors on each card, PCI bus and bus devices, cache
operation, byte order, interrupts, bus arbitration, memory controller, BIOS control,
system clocks, and system reset.
Microprocessors 2
The microprocessor on the 12” card is a Pentium-class microprocessor that runs at
100 MHz. It supports a 64-bit data path and a 32-bit address bus. The 7" card has a
100 MHz 5x86-class processor. It supports a 32-bit data path and a 32-bit address bus.
You should refer to the hardware reference manuals supplied by the microprocessor
manufacturer for further information on the different microprocessors.
PCI System Bus and Devices 2
The PCI bus on the PC system is a multiplexed address and data bus. The bus operates
synchronously at the same clock speed as the microprocessor bus (25 MHz or 33 MHz).
The bus supports burst reads and writes from the Mustard ASIC alternate bus master.
The key devices attached to the bus are the memory controller/bridge IC, the VGA
accelerator IC, and the Mustard ASIC. The PCI connector plugs into the PCI bus on the
Macintosh side of the system by means of the PCI slot in the Macintosh host computer.
“PCI Connector” beginning on page 35 provides detailed information about the PCI bus
signals.
Bus Snooping 2
Bus snooping is the method used by cache subsystems to monitor memory accesses
performed by different bus masters. This means that the internal microprocessor cache
can monitor activity on the PCI bus that is likely to change the contents of either the L1
or L2 cache memory.
The PC memory is fully cache coherent with the local PCI bus, and there are no cache
coherency problems with Macintosh memory. Bus snooping required by the Macintosh
host computer is done by the Macintosh and does not affect the PC system.