Technical Information 1-9
PCI Bus
The PCI bus consists of a multiplexed address and data bus (AD<31..0>) and control
circuitry. The PCI bus allows industry-standard PCI option boards to interface to the
system. The PCMC and LBXs link the PCI bus to the host bus, and PCI EISA bridge
component (PCEB) links the PCI bus to the EISA bus. PCI is a high bandwidth bus that is
processor independent. The on-board video, IDE, and SCSI controllers are on the PCI bus.
EISA Bus
The EISA bus consists of an address bus (SA<19..0>, LA<31..24>*, and <LA23..2>), a 32-
bit data bus (SD<31..0>), and control circuitry. The EISA bus is controlled by the PCEB
and EISA System component (ESC) and provides connection to industry standard
EISA/ISA option boards.
XD Bus
The XD bus (XD<7..0>) is an 8 bit data bus that provides connection to the keyboard
controller, ROM BIOS, and real-time clock (RTC). The XD bus is a buffered version of the
low order 8 bits of the EISA data bus (SD<31..0>). In the Neptune chipset, a distinction is
made between on-board and off-board peripherals. In general, on-board means that access
is expected to occur via the XD bus instead of the EISA bus. In this case, the access still
occurs on the EISA bus, but if the access is a read (I/O or memory), the ESC enables the
XD bus peripheral to drive the lower 8 bits of the EISA data bus (SD<7..0>).
System Memory Bus
The system memory bus consists of 11 bits of row/column addresses (MA<10..0>) that are
buffered to address banks 0, 1, 2, and 3. Each bank consists of two SIMMs. The PCMC
drives the system memory bus and memory control signals, which causes the data to be
driven to/from the LBXs (MD<63..0>).
Processor
The Image P90 system uses a 64-bit, 90-MHz Pentium microprocessor with a 60-MHz
external clock speed. The Image P100E uses a 64-bit, 100-MHz Pentium microprocessor
with a 66-MHz external clock speed. The technology package used for the microprocessor
is the 296-pin, staggered-pin-grid array (SPGA. The processor has 16 KB of write-back
internal cache, 8 KB for instructions and 8 KB for data. Also integrated into the processor
is a math coprocessor for complex calculations and processing tasks.
To use the Pentium processor’s power, the system features an optimized 64-bit memory
interface and complementary 256-KB secondary cache.
The Pentium processor is compatible with all 8-, 16-, and 32-bit software written for the
Intel386™, Intel486™, and Pentium processors.