12.232 bytes

Service Hints & Tips

Document ID: VLAR-3WKS9S

486 Processors - Questions and Answers

Applicable to: World-Wide

Question:
What is an IBM 486SLC processor?
Answer:
It is a single-speed version of the 486SLC2 (see below). It was only used in the IBM ThinkPad 700 notebooks.

Question:
At what clock speeds does the 486SLC operate?
Answer:
The only clock speed offered is 25MHz.

Question:
What is an IBM 486SLC2 processor?
Answer:
It is an IBM-developed derivative of the Intel 386SX chip, called the 486SLC2. The 486SLC2 processor includes the instruction set of the 486SX, rather than the 386. It only uses the same socket pin configuration as the 386SX.

Question:
How is the 486SLC2 different from the 386SLC?
Answer:
The 486SLC2 has a 16KB internal cache (versus 8K in the 386SLC) and clock doubling.

Question:
How does it differ from the Intel 486SL/486SX/486DX2 processors?
Answer:
The IBM 486SLC2 uses the same instruction set as the 486SX, and adds instructions for power-saving operation (like the 486SL, which came out after the 486SLC2). Also it has a 16K internal cache (versus 8K for the 486SL/SX/DX2) for improved performance, and like the 486DX2 comes in clock-doubling versions. Like the 486SL/SX, and unlike the 486DX2, the 486SLC2 does not include a floating-point (math coprocessor) unit, which adversely affects performance, compared to the 486DX2, when floating point math is used. Also, the 486SLC2 has a 16-bit external bus (to allow systems vendors to save money on motherboard design), which reduces performance slightly (about 10% versus a 32-bit bus); it also limits the system to no more than 16MB of RAM.

Question:
How fast is the 486SLC2 processor?
Answer:
The IBM 486SLC2 processor runs internally at twice the speed of the rest of the system, such as 40/20MHz, producing performance faster than a 25MHz 486DX, but less than a 50MHz 486DX. The performance of IBM's 40/20MHz 486SLC2 is up to 271% better than a 20MHz Intel 386SX, up to 99% faster than IBM's 20MHz 386SLC, up to 53% faster than a 20MHz Intel 486SX, and up to 20% faster than Intel's 25MHz 486SX processor. IBM's 50/25MHz 486SLC2 is somewhat faster than Intel's 486DX-33, but not as fast as the Intel 486DX2-50, due to the lack of a built-in floating point unit and the use of a 16-bit bus.

Question:
What if I need a math coprocessor?
Answer:
An Intel 387SX (or compatible) coprocessor may be added to your coprocessor socket. Performance, though, will still not be quite as good as the 486DX2, because an external 16-bit coprocessor running at the clock speed (20/25/33MHz) is not as fast as an internal 32-bit FPU running at the processor speed (2X the clock speed). On the other hand, a 486SLC2 with 387SX costs significantly less than a 486DX2.

Question:
How does the 486SLC2 processor perform against the Cyrix 486SLC?
Answer:
The 486SLC2 is more than twice as fast. In fact, even the IBM 386SLC outperforms the Cyrix 486SLC (NSTL Lotus benchmark).

Question:
How does this chip compare to Cyrix's 486SLC chip, in design and performance?
Answer:
The IBM 486SLC2 has clock-doubling and 16K internal cache. The Cyrix product has a 1K internal cache. The IBM 486SLC2 is clearly superior to Cyrix in all benchmarks we've run (Lotus, Word and Excel for Windows, using PC Week and PC Magazine benchmarks).

Question:
Wouldn't 32-bit applications run much better on 32-bit bus systems than one using the 486SLC2?
Answer:
The 486SLC2 processor, with 16K internal cache, will support 32-bit applications, with 32-bit data streams, with excellent performance.

Question:
At what clock speeds does the 486SLC2 operate?
Answer:
The current implementations of clock-doubling on the 486SLC2 are 40/20, 50/25, and 66/33MHz. The current implementation uses the clock of the system it is operating in (20/25/33MHz). This chip is similar in function to a 486DX2 as far as clock-doubling.

Question:
What is an IBM 486SLC3 processor?
Answer:
It is a clock-tripling version of the IBM 486SLC2.

Question:
How fast is the 486SLC3 processor?
Answer:
The IBM 486SLC3 processor is up to 40% faster than the 486SLC2 running at the same clock speed (e.g., 75/25 vs, 50/25). |

Question:
At what clock speeds does the 486SLC3 operate?
Answer:
The current implementations of clock-tripling on the 486SLC3 are 60/20, 75/25 and 100/33MHz, depending on the clock speed of the system in which it is operating (20/25/33MHz). The 486SLC3 was the industry's first clock-tripling processor, predating the Intel 486DX4. |

Question:
What if I need a math coprocessor for my 486SLC2/486SLC3-based system?
Answer:
An Intel 387SX (or compatible) coprocessor may be added (or a 386SL in the ThinkPad 700/700C).

Question:
What is an IBM 486BL2 or 486BL3 (Blue Lightning) processor?
Answer:
It is an IBM-developed derivative of the Intel 486SX chip that comes in two "flavors": the clock-doubling 486BL2 and clock-tripling 486BL3.

Question:
How do the 486BL2/BL3 compare to the IBM 486SLC2/SLC3 processors?
Answer:
Blue Lightning is essentially the same as the 486SLC2/486SLC3 processors, but uses a 32-bit external bus, like the 486DX2/DX4, for faster I/O. This also allows a Blue Lightning-equipped system to use more than 16MB of RAM (up to 4GB), a limitation of the 486SLCx processors. |

Question:
How does the 486BL2 compare to the Intel 486SX/486DX2 processors?
Answer:
Like the 486DX2, the 486BL2 comes in a 50/25MHz and 66/33MHz clock speeds, and offers a 32-bit external bus. Unlike the 486DX2, the 486BL2 doesn't contain an internal math coprocessor, but does include a 16K internal cache, compared to only 8K for the 486DX2. The overall result is better performance (at the same clock speed) for the 486DX2 in floating-point math-intensive calculations, but better performance in non-FP intensive situations (which is much more common for most users). Plus, the 486BL3 offers 75/25MHz and 100/33MHz clock-tripling versions, as described above, for even better performance than the DX2. Finally, unlike the DX2, the Blue Lightning contains power-saving circuitry similar to that in the 486SLCx processors, making it more suitable for laptop and "green PC" use.

Question:
How does the 486BL3 compare to Intel's 486DX4 processor?
Answer:
Both processors come in clock-tripling 75/25MHz and 100/33MHz speeds, both use 16K internal caches, and both use 3.3V technology for low power-consumption. No direct performance comparisons have been done. However, because the DX4 contains a clock-tripled math coprocessor and the 486BL3 does not, the DX4 should be much faster for floating point math operations. Integer operations should be roughly equivalent. Still, the 486BL3 chip is far less expensive than the 486DX2.

Question:
How fast are the 486BL2 and 486BL3?
Answer:
In composite benchmarks, which test a combination of floating-point and integer operations (an averaging of Norton, Landmark, Power Meter, Whetstone and 16/32-bit Dhrystone benchmarks), the following results were tabulated: Compared to an Intel 486DX-25, the 50/25MHz 486BL2 was 58% faster overall, and the 75/25MHz 486BL3 was more than twice as fast (216%). Against the Intel 50/25MHz 486DX2, the 50/25MHz 486BL2 was 2% faster overall, and the 75/25MHz 486BL3 was 38% faster.

Compared to an Intel 486DX-33, the 66/33MHz 486BL2 was 43% faster overall, and the 100/33MHz 486BL3 was
twice as fast (200%). Against the Intel 66/33MHz 486DX2, the 66/33MHz 486BL2 was 9% slower overall, and the
100/33MHz 486BL3 was 26% faster. For customers using primarily non-floating-point (integer) computations, both
clock-doubling 486BL2s offer similar performance to the 486DX2's, while both clock-tripling 486BL3 chips are
significantly faster than the 486DX2's, at a lower price.

Question:
What if I need a math coprocessor for my 486BL2/486BL3-based system?
Answer:
An Intel 387DX (or compatible) coprocessor may be added.

Question:
What will math coprocessor performance be like?
Answer:
Because the coprocessor is external to the Blue Lightning chip, and because it runs at the speed of the bus (25MHz or 33MHz) it won't be nearly as fast as a Floating Point Unit (FPU) built into the processor (such as a 486DX2/DX4), however for its extremely low price, a 387DX (or OEM plug-compatible equivalent) can produce a significant boost to the performance of application floating-point calculations. |

Question:
I have heard of IBM-made motherboards called "Azure," "Opal," and "Leopard." What processors do they use, and are they available as upgrades?
Answer:
These motherboards are made by IBM for use in OEM systems. Azure used the Blue Lightning (486BL2/BL3) processors, while Opal contained the 486SLC2 processor. They were used by a number of OEM vendors. The Leopard motherboards were designed for, and supplied, to Alaris Corporation only. They used either the 486SLC2 or 486SLC3 processors, depending on the model. None of these motherboards were available directly to end-users; only as part of OEM systems.

	Search Keywords
	Hint Category	Performance
	Date Created	20-07-98
	Last Updated	25-03-99
	Revision Date	25-03-2000
	Brand	IBM Options
	Product Family	Processor Upgrades
	Machine Type	486
	Model	All
	TypeModel
	Retain Tip (if applicable)
	Reverse Doclinks and Admin Purposes