6-2
RANGE REGISTERS
writethrough. The memory types are defined for specific address ranges based on range regis-
ters. The memory types currently defined, are shown in Table 6-1. The Pentium Pro processor
drives the memory type to the Pentium Pro processor bus in the second clock of the Request
Phase on the ATTR[3:0]# (attribute) pins.
Table 6-1. Pentium
®
Pro Processor Architecture Memory Types
ATTR[7:0]#
Encoding
Mnemonic
Name
Description
00000000
UC
uncacheable
Not cached. All reads and writes appear on the bus.
Reads and writes can have side effects, therefore no
speculative accesses are made to UC memory.
UC memory is useful for memory-mapped I/O.
00000100
WC
write-combining
Reads are not cached. Writes can be delayed and
combined. They are also weakly ordered resulting in
substantially higher write throughput. Reading WC
memory cannot have side effects and speculative
reads are allowed.
WC memory is useful for applications such as linear
frame buffers.
00000101
WT
write-through
Cacheable memory for which all writes are written
through to main memory.
Writing WT memory never causes a cache fill of an
invalid cache line and either invalidates or updates a
valid cache line.
00000110
WP
write-protected
Cacheable memory for which reads can hit the cache
and read misses cause cache fills, but writes bypass
the cache entirely.
00000111
WB
writeback
Cacheable memory for which write misses allocate
cache lines and writes are performed entirely in the
cache whenever possible.
WB memory is useful for normal memory, providing
the best performance and the least bus traffic for
many applications.
All others
—
Reserved
Attempting to write a reserved value into a memory
type field of an MTRR signals a #GP(0) fault and
does not update the MTRR.
Summary of Contents for Pentium Pro Family
Page 17: ...1 Component Introduction ...
Page 26: ...2 Pentium Pro Processor Architecture Overview ...
Page 27: ......
Page 36: ...3 Bus Overview ...
Page 62: ...4 Bus Protocol ...
Page 105: ...5 Bus Transactions and Operations ...
Page 126: ...6 Range Registers ...
Page 131: ...7 Cache Protocol ...
Page 135: ...8 Data Integrity ...
Page 148: ...9 Configuration ...
Page 161: ...10 Pentium Pro Processor Test Access Port TAP ...
Page 172: ...11 Electrical Specifications ...
Page 201: ...12 GTL Interface Specification ...
Page 229: ...13 3 3V Tolerant Signal Quality Specifications ...
Page 233: ...14 Thermal Specifications ...
Page 239: ...15 Mechanical Specifications ...
Page 241: ...15 2 MECHANICAL SPECIFICATIONS s Figure 15 1 Package Dimensions Bottom View ...
Page 252: ...16 Tools ...
Page 260: ...16 8 TOOLS Figure 16 4 Generic MP System Layout for Debug Port Connection ...
Page 264: ...17 OverDrive Processor Socket Specification ...
Page 290: ...A Signals Reference ...
Page 320: ...Index ...
Page 328: ......