HP Vectra XU 6/XXX HP Vectra XU 6/xxx, Guide to Optimizing performance - Page 29

Why 16-bit Applications, are Slower

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1 Your PC's Performance Features Benefits of 32-bit Applications Why 16-bit Applications When executing 16-bit instructions, the Pentium Pro processor is are Slower limited by two constraints. First, the Pentium Pro cannot mix 32-bit and 16-bit instructions in a pipeline. Second, at any moment only one 16-bit instruction can normally be present in a pipeline. When running a 16-bit application, all instructions are 16-bits and so each instruction is executed singly, without use of the pipeline's queuing facility. In effect, the pipeline is not used. Since the pipeline is the processor's most important means of accelerating instruction execution, the negative impact on performance is significant. Processor pipeline Only one 16-bit instruction can be in the pipeline at once Next instruction waiting to enter the pipeline Instruction execution steps NOTE For the reasons explained above, HP does not recommend using your PC to run 16-bit applications. Best performance can only be obtained when running 32-bit applications. English 23

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English
23
1
Your PC’s Performance Features
Benefits of 32-bit Applications
Why 16-bit Applications
are Slower
When executing 16-bit instructions, the Pentium Pro processor is
limited by two constraints. First, the Pentium Pro cannot mix 32-bit and
16-bit instructions in a pipeline. Second, at any moment only one 16-bit
instruction can normally be present in a pipeline.
When running a 16-bit application, all instructions are 16-bits and so
each instruction is executed singly, without use of the pipeline's
queuing facility. In effect, the pipeline is not used. Since the pipeline is
the processor's most important means of accelerating instruction
execution, the negative impact on performance is significant.
NOTE
For the reasons explained above, HP does not recommend using your
PC to run 16-bit applications. Best performance can only be obtained
when running 32-bit applications.
Processor pipeline
Instruction
execution steps
Only one 16-bit instruction can be in the pipeline at once
Next instruction
waiting to enter
the pipeline