From Wikipedia, the free encyclopedia
Computer architecture terminology
In
personal computer
microprocessor
architecture, a
back-side bus
(
BSB
), or
backside bus
, was a
computer bus
used on early Intel platforms to connect the
CPU
to
CPU cache memory
, usually off-die L2. If a design utilizes a back-side bus along with a
front-side bus
(FSB), the design is said to use a
dual-bus architecture
, or in
Intel
's terminology
Dual Independent Bus
(DIB)
[1]
architecture. The back-side bus architecture evolved when newer processors like
the second-generation Pentium III
began to incorporate on-die L2 cache, which at the time was advertised as
Advanced Transfer Cache
, but Intel continued to refer to the Dual Independent Bus till the end of Pentium III.
[2]
History
[
edit
]
BSB is an improvement over the older practice of using a single
system bus
, because a single bus typically became a severe
bottleneck
as CPUs and memory speeds increased. Due to its dedicated nature, the back-side bus can be optimized for communication with cache, thus eliminating protocol overheads and additional signals that are required on a general-purpose bus. Furthermore, since a BSB operates over a shorter distance, it can typically operate at higher clock speeds, increasing the computer's overall performance.
Cache connected with a BSB was initially external to the microprocessor
die
, but now is usually on-die.
[3]
In the latter case, the BSB
clock
frequency is typically equal to the processor's,
[4]
and the back-side bus can also be made much wider (256-bit, 512-bit) than either off-chip or on-chip FSB.
[
clarification needed
]
The dual-bus architecture was used in a number of designs, including the
IBM
and
Freescale
(formerly the semiconductor division of
Motorola
)
PowerPC
processors (certain PowerPC
604
models, the
PowerPC 7xx
family,
[5]
and the Freescale
7xxx
line), as well as the
Intel
Pentium Pro
,
Pentium II
and early
Pentium III
processors,
[6]
which used it to access their L2 cache (earlier Intel processors accessed the L2 cache over the FSB, while later processors moved it on-chip).
See also
[
edit
]
References
[
edit
]
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General
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Standards
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Storage
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Peripheral
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Audio
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Portable
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Embedded
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Interfaces are listed by their speed in the (roughly) ascending order, so the interface at the end of each section should be the fastest.
Category
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