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3 System Board (P/Ns D3657-63001 and D3661-63001)
Principal Components and Features
Data Path Unit (SB82438FX)
The SB82438FX component contains a 64-bit data path between the host
bus and main memory. A 4×64-bit deep buffer provides 3-1-1-1 writes to
main memory.
This buffer is used for:
• writes from processor to main memory
• level-two cache write-back cycles
• transfers from PCI to main memory.
1.
The Pentium’s internal cache has a 32-byte line size, which is four times the width of the Pen-
tium’s host data bus. Burst reads and writes by the Pentium involve a full cache line, and so re-
quire four back-to-back cycles to complete. The first cycle in each burst of four always requires
more time to complete than the three subsequent cycles. This is because the first cycle includes
the addressing phase and precharge timing (for memory).
PCI master interface ❒ Provides for programmable PCI bus memory regions in
memory address map
❒ Supports PCI bus burst cycles for 64-bit and 32-bit misaligned
Pentium reads and writes
❒ Optional posting of PCI memory and I/O writes
❒ Optional buffering of PCI memory writes
❒ Optional read-ahead for processor to PCI accesses
PCI bus arbiter ❒ Supports PCI bus arbitration for up to four masters
❒ Supports rotating priority scheme
Function Features