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Compaq Workstations - Key Technologies
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Dual-Peer PCI Buses
The Compaq Professional Workstation 6000 also uses dual-peer PCI buses to increase system
I/O bandwidth. A single PCI bus provides I/O bandwidth of 133MB/second that must be shared
by many key peripherals such as the graphics controller, hard drive, and NIC. With dual-peer
PCI buses, each bus can provide peek bandwidth in parallel with the other controller, allowing
an aggregate I/O bandwidth of 267MB/second. This implementation provides twice the
bandwidth of single bus architectures. Also, dual PCI buses allow key peripherals to be
connected to separate buses to balance overall system throughput. The dual PCI buses also allow
for greater system I/O integration and expandability by supporting up to 12 PCI devices which is
twice the number supported on single bus implementations. This allows the Compaq
Professional Workstation 6000 to deliver six PCI-based I/O expansion slots while also
integrating other PCI components such as the SCSI and network controllers on the system board.
Diagram 3: Dual-Peer PCI Buses.
Optimized Multiprocessing Support
Finally, with dual memory controllers and dual-peer PCI buses, the Compaq Professional
Workstation 6000 is able to deliver optimized multiprocessing support. The Intel Pentium II
processor enables multiprocessor support by including circuitry in the processor that determines
how multiple processors can share the CPU bus. However, most multiprocessing
implementations in the Intel based Windows NT workstation market take advantage of this
support by simply adding an additional processor to an already existing desktop design. Compaq
takes multiprocessing to the next step with the Compaq Highly Parallel System Architecture by
enhancing memory and I/O bandwidth as well. Multiprocessor Systems designed without the
Compaq Highly Parallel System Architecture will quickly encounter a bottleneck as the multiple
processors try to access the other system resources, such as memory and I/O subsystems, that
have not been enhanced to accommodate the additional data traffic. The Compaq Highly Parallel
System Architecture significantly reduces these bottlenecks by incorporating enhanced
subsystem resources, such as dual memory controllers and dual- peer PCI buses, to accommodate
the increased data traffic from the multiple CPUs.
