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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 Intel386â„¢ 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.