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Revision 2.1
It is assumed that typical low bandwidth, after-market add-ins will remain on the
standard I/O expansion buses such as ISA, EISA, or MC. One component (or set of
components) on PCI may generate the standard I/O expansion bus used in the system. In
some mobile or client systems, a standard expansion bus may not be required.
1.5. PCI Local Bus Features and Benefits
The PCI Local Bus was specified to establish a high performance local bus standard for
several generations of products. The PCI specification provides a selection of features
that can achieve multiple price-performance points and can enable functions that allow
differentiation at the system and component level. Features are categorized by benefit as
follows:
High Performance • Transparent upgrade from 32-bit data path at 33 MHz
(132 MB/s peak) to 64-bit data path at 33 MHz
(264 MB/s peak) and from 32-bit data path at 66 MHz
(264 MB/s peak) to 64-bit data path at 66 MHz
(528 MB/s peak).
• Variable length linear and cacheline wrap mode bursting
for both read and writes improves write dependent graphics
performance.
• Low latency random accesses (60-ns write access latency
for 33 MHz PCI or 30-ns for 66 MHz PCI to slave
registers from master parked on bus).
• Capable of full concurrency with processor/memory
subsystem.
• Synchronous bus with operation up to 33 MHz or 66 MHz.
• Hidden (overlapped) central arbitration.
Low Cost • Optimized for direct silicon (component) interconnection;
i.e., no glue logic. Electrical/driver (i.e., total load) and
frequency specifications are met with standard ASIC
technologies and other typical processes.
• Multiplexed architecture reduces pin count (47 signals for
target; 49 for master) and package size of PCI components,
or provides for additional functions to be built into a
particular package size.
• Single PCI add-in card works in ISA-, EISA-, or
MC-based systems (with minimal change to existing
chassis designs), reducing inventory cost and end user
confusion.
Ease of Use • Enables full auto configuration support of PCI Local Bus
add-in boards and components. PCI devices contain
registers with the device information required for
configuration.
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