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Digital Electronics
from the Pentium itself. These include Pentium Pro, Pentium II, Pentium M, Pentium D and Pentium
Extreme Edition.
The Pentium processor has two primary operating modes and a system management mode. The
operating mode determines which instructions and architectural features are accessible. These modes
are as follows:
1. Protected mode. This is the native state of the microprocessor. In this mode, all instructions and
architectural features are available, providing the highest performance and capability.
2. Real address mode. This mode provides the programming environment of the Intel 8086 processor,
with a few extensions. Reset initialization places the processor in real mode where, with a single
instruction, it can switch to protected mode.
3. System management mode. It provides an operating system and application independent transparent
mechanism to implement system power management and OEM differentiation features. SMM is
entered through activation of an external interrupt pin (SMI#), which switches the CPU to a separate
address space while saving the entire content of the CPU.
13.12.1 Salient Features
The Pentium series (P5, P54 and P54C) of microprocessors has the following advanced features:
1. Superscalar execution. The Intel 486 processor can execute only one instruction at a time.
With superscalar execution, the Pentium processor can sometimes execute two instructions
simultaneously.
2. Pipeline architecture. Like the Intel 486 processor, the Pentium processor executes instructions in
five stages. This staging, or pipelining, allows the processor to overlap multiple instructions so that
it takes less time to execute two instructions in a row. Because of its superscalar architecture, the
Pentium processor has two independent processor pipelines.
3. Branch target buffer. The Pentium processor fetches the branch target instruction before it executes
the branch instruction.
4. Dual 8 kB on-chip caches. The Pentium processor has two separate 8 kB caches on chip, one for
instructions and the other for data. This allows the Pentium processor to fetch data and instructions
from the cache simultaneously.
5. Write-back cache. When data are modified, only the data in the cache are changed. Memory data are
changed only when the Pentium processor replaces the modified data in the cache with a different
set of data.
6. 64-bit bus. With its 64-bit wide external data bus (in contrast to the Intel 486 processor’s 32-bit
wide external bus), the Pentium processor can handle up to twice the data load of the Intel 486
processor at the same clock frequency.
7. Instruction optimization. The Pentium processor has been optimized to run critical instructions in
fewer clock cycles than the Intel 486 processor.
8. Floating-point optimization. The Pentium processor executes individual instructions faster through
execution pipelining, which allows multiple floating-point instructions to be executed at the same
time.
9. Pentium extensions. The Pentium processor has fewer instruction set extensions than the Intel 486
processors. The Pentium processor also has a set of extensions for multiprocessor (MP) operation.
This makes a computer with multiple Pentium processors possible.
Digital Electronics
from the Pentium itself. These include Pentium Pro, Pentium II, Pentium M, Pentium D and Pentium
Extreme Edition.
The Pentium processor has two primary operating modes and a system management mode. The
operating mode determines which instructions and architectural features are accessible. These modes
are as follows:
1. Protected mode. This is the native state of the microprocessor. In this mode, all instructions and
architectural features are available, providing the highest performance and capability.
2. Real address mode. This mode provides the programming environment of the Intel 8086 processor,
with a few extensions. Reset initialization places the processor in real mode where, with a single
instruction, it can switch to protected mode.
3. System management mode. It provides an operating system and application independent transparent
mechanism to implement system power management and OEM differentiation features. SMM is
entered through activation of an external interrupt pin (SMI#), which switches the CPU to a separate
address space while saving the entire content of the CPU.
13.12.1 Salient Features
The Pentium series (P5, P54 and P54C) of microprocessors has the following advanced features:
1. Superscalar execution. The Intel 486 processor can execute only one instruction at a time.
With superscalar execution, the Pentium processor can sometimes execute two instructions
simultaneously.
2. Pipeline architecture. Like the Intel 486 processor, the Pentium processor executes instructions in
five stages. This staging, or pipelining, allows the processor to overlap multiple instructions so that
it takes less time to execute two instructions in a row. Because of its superscalar architecture, the
Pentium processor has two independent processor pipelines.
3. Branch target buffer. The Pentium processor fetches the branch target instruction before it executes
the branch instruction.
4. Dual 8 kB on-chip caches. The Pentium processor has two separate 8 kB caches on chip, one for
instructions and the other for data. This allows the Pentium processor to fetch data and instructions
from the cache simultaneously.
5. Write-back cache. When data are modified, only the data in the cache are changed. Memory data are
changed only when the Pentium processor replaces the modified data in the cache with a different
set of data.
6. 64-bit bus. With its 64-bit wide external data bus (in contrast to the Intel 486 processor’s 32-bit
wide external bus), the Pentium processor can handle up to twice the data load of the Intel 486
processor at the same clock frequency.
7. Instruction optimization. The Pentium processor has been optimized to run critical instructions in
fewer clock cycles than the Intel 486 processor.
8. Floating-point optimization. The Pentium processor executes individual instructions faster through
execution pipelining, which allows multiple floating-point instructions to be executed at the same
time.
9. Pentium extensions. The Pentium processor has fewer instruction set extensions than the Intel 486
processors. The Pentium processor also has a set of extensions for multiprocessor (MP) operation.
This makes a computer with multiple Pentium processors possible.