Intel architecture ia-32 User Manual
Vol. 3A 10-13
MEMORY CACHE CONTROL
Table 10-5. Cache Operating Modes
CD
NW
Caching and Read/Write Policy
L1
L2/L3
1
0
0
Normal Cache Mode. Highest performance cache operation.
- Read hits access the cache; read misses may cause replacement.
- Write hits update the cache.
- Only writes to shared lines and write misses update system memory.
- Write misses cause cache line fills.
- Write hits can change shared lines to modified under control of the
MTRRs and with associated read invalidation cycle.
- (Pentium processor only.) Write misses do not cause cache line fills.
- (Pentium processor only.) Write hits can change shared lines to
exclusive under control of WB/WT#.
- Invalidation is allowed.
- External snoop traffic is supported.
- Read hits access the cache; read misses may cause replacement.
- Write hits update the cache.
- Only writes to shared lines and write misses update system memory.
- Write misses cause cache line fills.
- Write hits can change shared lines to modified under control of the
MTRRs and with associated read invalidation cycle.
- (Pentium processor only.) Write misses do not cause cache line fills.
- (Pentium processor only.) Write hits can change shared lines to
exclusive under control of WB/WT#.
- Invalidation is allowed.
- External snoop traffic is supported.
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
0
1
Invalid setting.
Generates a general-protection exception (#GP) with an error code of 0.
Generates a general-protection exception (#GP) with an error code of 0.
NA
NA
1
0
No-fill Cache Mode. Memory coherency is maintained.
- (Pentium 4 and Intel Xeon processors.) State of processor after a power
up or reset.
- Read hits access the cache; read misses do not cause replacement
(see Pentium 4 and Intel Xeon processors reference below).
- Write hits update the cache.
- Only writes to shared lines and write misses update system memory.
- Write misses access memory.
- Write hits can change shared lines to exclusive under control of the
MTRRs and with associated read invalidation cycle.
- (Pentium processor only.) Write hits can change shared lines to
exclusive under control of the WB/WT#.
- (Pentium 4, Intel Xeon, and P6 family processors only.) Strict memory
ordering is not enforced unless the MTRRs are disabled and/or all
memory is referenced as uncached (see Section 7.2.4., “Strengthening
or Weakening the Memory Ordering Model”).
- Invalidation is allowed.
- External snoop traffic is supported.
- (Pentium 4 and Intel Xeon processors.) State of processor after a power
up or reset.
- Read hits access the cache; read misses do not cause replacement
(see Pentium 4 and Intel Xeon processors reference below).
- Write hits update the cache.
- Only writes to shared lines and write misses update system memory.
- Write misses access memory.
- Write hits can change shared lines to exclusive under control of the
MTRRs and with associated read invalidation cycle.
- (Pentium processor only.) Write hits can change shared lines to
exclusive under control of the WB/WT#.
- (Pentium 4, Intel Xeon, and P6 family processors only.) Strict memory
ordering is not enforced unless the MTRRs are disabled and/or all
memory is referenced as uncached (see Section 7.2.4., “Strengthening
or Weakening the Memory Ordering Model”).
- Invalidation is allowed.
- External snoop traffic is supported.
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
1
1
Memory coherency is not maintained.
2
- (P6 family and Pentium processors.) State of the processor after a
power up or reset.
- Read hits access the cache; read misses do not cause replacement.
- Write hits update the cache and change exclusive lines to modified.
- Shared lines remain shared after write hit.
- Write misses access memory.
- Invalidation is inhibited when snooping; but is allowed with INVD and
WBINVD instructions.
- External snoop traffic is supported.
power up or reset.
- Read hits access the cache; read misses do not cause replacement.
- Write hits update the cache and change exclusive lines to modified.
- Shared lines remain shared after write hit.
- Write misses access memory.
- Invalidation is inhibited when snooping; but is allowed with INVD and
WBINVD instructions.
- External snoop traffic is supported.
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
NOTES:
1. The L2/L3 column in this table is definitive for the Pentium 4, Intel Xeon, and P6 family processors. It is
intended to represent what could be implemented in a system based on a Pentium processor with an
external, platform specific, write-back L2 cache.
external, platform specific, write-back L2 cache.
2. The Pentium 4 and Intel Xeon processors do not support this mode; setting the CD and NW bits to 1
selects the no-fill cache mode.