64-bit PCI at 66 MHz - From Dell's Wesite, avail from Intel and AMI
Matthew A. Earley
MB's from AMI, but they run at 33 MHz.
If you know of any others please let me know with an email.
-Matthew
This is from Dells's website:
http://www.dell.com/r&d/vectors/vect_3-2/v3-2apcib.htm
64-Bit Extension
The 64-bit extension, defined in PCI specification 2.1, adds an extension to
the PCI bus connector that provides the extra pins needed to support 64-bit
data and address transfers. Signals in these larger connectors are arranged
so that a 32-bit PCI card interfaces only with the original 32-bit
connector, making it capable of operating (in 32-bit mode) on the 64-bit bus
without modification. A 64-bit PCI card can operate on either a 32-bit or
64-bit bus, defaulting to the 32-bit mode of operation on a 32-bit bus. A
64-bit PCI card also defaults to the 32-bit mode of operation on a 64-bit
bus unless a 64-bit transaction is negotiated with another PCI device
capable of 64-bit transfers. Figure 2 shows how 32- and 64-bit PCI cards
interface with either 32- or 64-bit PCI connectors.
A 64-bit PCI bus operating at 33 MHz supports data transfers up to 266
megabytes per second (MB/sec), while a 32-bit PCI bus operating at the same
speed supports data transfers only up to 133 MB/sec. With its increased data
transfer rate, the 64-bit PCI bus is better equipped to support new fast I/O
technologies such as Gigabit Ethernet and Fibre Channel, both of which could
saturate a 32-bit PCI bus with their 100-MB/sec data transfer capability.
Table 1 compares the peak data transfer rates of 32-bit and 64-bit PCI buses
operating at 33 MHz and 66 MHz. Most high-end Intel-based server products
will include 64-bit PCI buses by mid- to late 1998.
Bus Frequency Peak Transfer Rate 32-Bit Bus 64-Bit Bus
33 MHz* 133 MB/sec 266 MB/sec
66 MHz* 266 MB/sec 532 MB/sec
* Actual clock speeds are 33.33 MHz and 66.66 MHz.
Table 1. PCI Bus Data Transfer Rates
66-MHz Extension
The 66-MHz extension, defined in PCI specification 2.1, provides data
transfer rates of up to 266 MB/sec on a 32-bit bus and up to 532 MB/sec on a
64-bit bus. Although a 33-MHz PCI bus can support as many as four or five
PCI cards, timing restrictions and physical bus loading prevent a 66-MHz PCI
bus from supporting more than two PCI devices. To increase the number of PCI
devices supported, manufacturers often implement multiple peer buses.
Multiple peer buses can provide a means for using both 33- and 66-MHz PCI
cards in a server without compromising the performance of the 66-MHz
devices. Another benefit of multiple peer buses is that they can improve the
performance of the system and any attached PCI devices by providing multiple
paths to system memory.
When a 33-MHz PCI device is connected to a 66-MHz PCI bus, the bus and all
devices connected to the bus--including any 66-MHz PCI devices--default to
33-MHz operation. Some of Dell's new servers, to be introduced in late 1998
and early 1999, will feature 33- and 66-MHz peer buses, which will allow
customers to use legacy 33-MHz PCI devices in their servers without
compromising the performance of 66-MHz devices. Most 66-MHz buses will be 64
bits wide for optimum performance. The 66-MHz PCI bus is ideal for cluster
interconnections where low latency is critical for the heartbeat signals and
data passed between clustered servers.