personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...

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 it along with a

front-side bus A front-side bus (FSB) is a computer communication interface (bus) that was often used in Intel-chip-based computers during the 1990s and 2000s. The EV6 bus served the same function for competing AMD CPUs. Both typically carry data between the ...

(FSB), it is said to use a dual-bus architecture, or in

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...

's terminology ''

Dual Independent Bus A system bus is a single Bus (computing), computer bus that connects the major components of a computer system, combining the functions of a Memory bus, data bus to carry information, an address bus to determine where it should be sent or read fro ...

'' (DIB) 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. Intel MMC2 arch

History

BSB is an improvement over the older practice of using a single system bus, because a single bus typically became a severe

bottleneck Bottleneck literally refers to the narrowed portion (neck) of a bottle near its opening, which limit the rate of outflow, and may describe any object of a similar shape. The literal neck of a bottle was originally used to play what is now known as ...

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 Die, as a verb, refers to death, the cessation of life. Die may also refer to: Games * Die, singular of dice, small throwable objects used for producing random numbers Manufacturing * Die (integrated circuit), a rectangular piece of a semicondu ...

, but now is usually on-die. In the latter case, the BSB

clock A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and t ...

frequency is typically equal to the processor's, and the back-side bus can also be made much wider (256-bit, 512-bit) than either off-chip or on-chip FSB. P2 Deschutes open front

The dual-bus architecture was used in a number of designs, including the IBM and

Freescale Freescale Semiconductor, Inc. was an American semiconductor manufacturer. It was created by the divestiture of the Semiconductor Products Sector of Motorola in 2004. Freescale focused their integrated circuit products on the automotive, embed ...

(formerly the semiconductor division of

Motorola Motorola, Inc. () was an American multinational telecommunications company based in Schaumburg, Illinois, United States. After having lost $4.3 billion from 2007 to 2009, the company split into two independent public companies, Motorol ...

)

PowerPC PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., App ...

processors (certain PowerPC

604 __NOTOC__ Year 604 (Roman numerals, DCIV) was a leap year starting on Wednesday (link will display the full calendar) of the Julian calendar. The denomination 604 for this year has been used since the early medieval period, when the Anno Domini ...

models, the

PowerPC 7xx The PowerPC 7xx is a family of third generation 32-bit PowerPC microprocessors designed and manufactured by IBM and Motorola (spun off as Freescale Semiconductor bought by NXP Semiconductors). This family is called the PowerPC G3 by its well-kn ...

family, and the Freescale 7xxx line), as well as the

Pentium Pro The Pentium Pro is a sixth-generation x86 microprocessor developed and manufactured by Intel and introduced on November 1, 1995. It introduced the P6 microarchitecture (sometimes termed i686) and was originally intended to replace the original ...

Pentium II The Pentium II brand refers to Intel's sixth-generation microarchitecture (" P6") and x86-compatible microprocessors introduced on May 7, 1997. Containing 7.5 million transistors (27.4 million in the case of the mobile Dixon with 256 KB ...

and early

Pentium III The Pentium III (marketed as Intel Pentium III Processor, informally PIII or P3) brand refers to Intel's 32-bit x86 desktop and mobile CPUs based on the sixth-generation P6 microarchitecture introduced on February 28, 1999. The brand's initial ...

processors, 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).

References

{{CPU technologies Computer buses

History

See also

References