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Pentium® Pro Processor Frequently Asked
Questions
Here is a list of Pentium® Pro processor Frequently
Asked Questions and answers. Some answers may link
you to another location on our website for further details.
Q1: The Pentium Pro processor looks different than
other chips. Will a Pentium Pro processor fit into a
Pentium processor socket?
Q2: What about the thermal and electrical
specifications? How hot will it run? At what voltage
does it operate?
Q3: What kind of performance can I expect from the
Pentium Pro processor?
Q4: What are the advantages of an in-package L2
cache?
Q5: Will multi-processing be easier with the Pentium
Pro processor?
Q6: Is the Pentium Pro processor a 64-bit processor?
Does it support 64-bit integer instructions?
Q7: Is there a new instruction used by the Pentium Pro
processor? What does it do?
Q8: The Pentium Pro processor has about 21 million
transistors in total. Does this put the Pentium Pro
processor at a cost disadvantage? Is it difficult to
manufacture?
Q1: The Pentium Pro processor looks different than
other chips. Will a Pentium Pro processor fit into a
Pentium processor socket?
No, the Pentium Pro processor bus is quite different
from a Pentium processor bus, so it is not designed to
be pin compatible. The component bus of a Pentium
processor is designed to interface to an external L2
cache and includes features to optimize CPU-to-cache
data transfers. In contrast, the first Pentium Pro
processor includes a 256KB L2 cache in the same
package and the CPU communicates with its L2 cache
using a private internal bus. The component bus of a
Pentium Pro processor is designed to interface to a
cache coherent memory bus and includes features to
optimize cache-to-memory data transfers.
Q2: What about the thermal and electrical
specifications? How hot will it run? At what voltage
does it operate?
Detailed electrical information is available in our
Pentium Pro processor data sheet.
Q3: What kind of performance can I expect from
the Pentium Pro processor?
Detailed information is available in the Pentium Pro
processor performance brief.
Q4: What are the advantages of an in-package L2
cache?
Having the L2 cache in the package not only simplifies
system design and saves space, it also means the CPU
core can communicate with the L2 cache at full speed.
Additionally the cache is non-blocking which means that
transactions on the Pentium Pro processor bus don't
stall the processor or block subsequent bus
transactions. For example, when a cache miss occurs,
the Pentium Pro processor continues to process other
instructions while initiating a bus transaction to satisfy
the cache miss; these instructions could generate
additional cache misses which could cause mores bus
transactions. The Pentium Pro processor can maintain
up to four of these outstanding transactions.
Q5: Will multi-processing be easier with the
Pentium Pro processor?
The Pentium Pro processor bus was designed to
support multiple Pentium Pro processors connected in
parallel. The Pentium Pro processor component bus is a
symetric multiprocessing bus and includes full support
for the MESI protocol. 'Glueless' MP Pentium Pro
processor system designs are supported; that is, no
additional system logic is required for multi-processing
since the Pentium Pro processor includes all of the
logic required to directly support the interconnection of
up to four Pentium Pro processors. This means that it's
very easy - and cost-effective - for system designers to
include multiple Pentium Pro processor processors,
essentially by just providing sockets for the additional
processors.
Q6: Is the Pentium Pro processor a 64-bit
processor? Does it support 64-bit integer
instructions?
No. Like all Intel processors since the Intel386™
processor, the Pentium Pro processor is a true 32-bit
processor. The general purpose registers are the same
as on previous generations of Intel Architecture
processors and the instruction set is supported with
only one new instruction being introduced. However,
there are a variety of wider datapaths both inside and
outside the chip. One visible feature that is sometimes
misinterpreted is that the Pentium Pro processor, like
the Pentium processor, has an external 64-bit bus in
order to communicate more efficiently with system
memory. This wider external datapath increases
bandwidth between the Pentium Pro processor and the
system, but doesn't make the Pentium Pro processor a
64-bit machine.
Q7: Is there a new instruction used by the Pentium
Pro processor? What does it do?
A conditional move instruction was added which may be
used by compiler writers as an alternate to a "test an
set" construct. This allows a data dependent branch to
be eliminated. The resulting code will be more
predictable by the processor and will thus deliver higher
performance.
Q8: The Pentium Pro processor has about 21
million transistors in total. Does this put the
Pentium Pro processor at a cost disadvantage? Is
it difficult to manufacture?
No. The Pentium Pro processor CPU core has 5.5
million transistors, and the L2 cache contains 15.5
million.
The main determinant for product manufacturability and
cost is the die size, which is in large part a result of the
process technology that the product is manufactured
on. The first Pentium Pro processor will be built on the
same process as today's Pentium processors--including
the high-volume .6 micron process, and the
advanced .35 micron process. The .35 micron process
enables higher clock frequencies and higher
performance, but also makes the Pentium Pro
processor's die size much smaller and easier to
manufacture.
The 15.5 million number for the L2 cache is also
somewhat misleading. Since the L2 cache is a very
regular uniform structure, the transistors may be placed
more densely resulting in a relatively small die area.
While the L2 cache contains nearly three times the
transistor count of the CPU core, the die size is actually
smaller than the .6 micron version of the Pentium Pro
processor CPU.