IBM 486SLC
| Company type | Division |
|---|---|
| Industry | Semiconductor |
| Founded | 1991 |
| Products | 386SLC, 486SLC, 486BL (Blue Lightning) |
| Owner | IBM |
The 386SLC represents IBM's 1991 development of an Intel-licensed variant of the 386SX, featuring a 32-bit internal architecture, 16-bit external data bus, and 24-bit memory addressing. It incorporated power-saving capabilities alongside an 8KB on-chip CPU cache, achieving performance levels comparable to the higher-priced 386DX processors at equivalent clock frequencies. Internally dubbed "Super Little Chip", this processor was integrated into the IBM PS/2 35, 40, and 56 Series as well as the IBM PS/ValuePoint 325T models. Despite this, its market penetration remained limited due to IBM’s licensing terms with Intel, which confined CPU distribution to bundled system or upgrade board sales. Additionally, it was available as an optional upgrade for IBM PS/2 25 Series systems initially outfitted with Intel 8086 CPUs.
Design and Technology
Manufactured using complementary metal oxide semiconductor (CMOS) technology, the IBM 386SLC featured a die size of 161 mm2 and came in clock speeds of 16, 20, and 25 MHz. The highest-speed variant consumed just 2.5 watts of power, making it particularly suitable for portable computing devices such as laptops.
While electrically compatible with the i386SX and i386DX buses, the SLC and DLC models are not pin-compatible and thus cannot be directly swapped with those Intel processors.
IBM 486SLC
Launched in 1992, the IBM 486SLC was an upgraded iteration of the 386SLC, built upon the Intel architecture. It incorporated a 16KB L1 cache, supported the i486 instruction set, contained approximately 1.349 million transistors on a compact 69 mm2 die, and was housed in a 100-pin BQFP package with a front-side bus running at 33 MHz. Subsequent variants included clock-doubled models (486SLC2) operating at 50 and 66 MHz and clock-tripled versions (486SLC3) reaching speeds of 60, 75, and 100 MHz. In terms of raw clock-for-clock performance, it surpassed contemporaneous Cyrix processors bearing similar nomenclature and matched equivalently clocked 486SX chips in legacy 16-bit environments. Nonetheless, its restricted memory bandwidth (16-bit), capped memory addressing at 16 MB, and lack of integrated floating-point unit (FPU) constrained its effectiveness under advancing 32-bit operating systems such as Windows 95.
The presence of a standalone clock-tripled variant of the 486SLC3 remains uncertain; existing specimens are reportedly modified earlier models with certain address lines disconnected.
IBM 486BL (Blue Lightning)
The IBM 486BL marked a fully 32-bit evolution of the earlier 486SLC design, integrating roughly 1.4 million transistors on an 82 mm2 die fabricated using a 0.8 μm CMOS process. Encased in a 132-pin QFP, IBM introduced clock-doubled (486BL2) and clock-tripled (486BL3) versions ranging from 50 to 100 MHz in July 1993, distributing these processors exclusively through its own channels.
Later Blue Lightning CPUs designed for Socket 3 platforms utilized a different core derived from the Cyrix Cx486, packaged in a larger 168-pin PGA format. These units can be distinguished by "DX" markings that set them apart from earlier Blue Lightning models roughly equivalent to i486SX processors based on the IBM/Intel blueprint.
Market confusion arose due to IBM’s adoption of Cyrix cores in later products, limited transparency regarding initial models, and ambiguous part numbering schemes. Early Blue Lightning chips are frequently labeled "486DLC" by enthusiasts despite IBM never officially assigning this name. This "486DLC" term actually originates from Cyrix’s separate product lineup but has become an informal identifier due to the absence of alternative designations. Differences in packaging and branding aid in clearly differentiating these processor families.
See also
- Intel 386
- IBM PS/2
- IBM PS/ValuePoint
- IBM ThinkPad
- IBM 5x86C – derived from the Cyrix architecture
- IBM Personal Computer