IBM 386SLC
| Company type | Microprocessor |
|---|---|
| Industry | Semiconductor |
| Founded | 1991 |
| Products | 386SLC, 486SLC, 486BL (Blue Lightning) microprocessors |
| Owner | IBM |
The 386SLC represents IBM's licensed adaptation of the 386SX processor (featuring a 32-bit internal architecture, 16-bit external bus, and 24-bit memory addressing), developed and produced in 1991 under license from Intel. It incorporated power-saving capabilities alongside an 8KB internal CPU cache, achieving performance levels on par with higher-priced 386DX processors operating at identical clock frequencies. Internally dubbed the "Super Little Chip" by IBM engineers, this CPU was integrated into the IBM PS/2 35, 40, and 56 Series as well as the IBM PS/ValuePoint 325T models. However, its market reach remained limited due to contractual restrictions preventing IBM from selling the processors independently of complete systems or upgrade kits. Additionally, it served as an upgrade option for IBM PS/2 25 Series machines originally outfitted with 8086 CPUs.
Design and Technology
Manufactured using complementary metal oxide semiconductor (CMOS) technology, the IBM 386SLC featured a die size of 161 mm² and was offered in clock speeds of 16, 20, and 25 MHz. The highest-speed variant consumed merely 2.5 watts of power, making it particularly suitable for use in laptops and other portable computing devices.
While bus-compatible with both i386SX and i386DX processors, the SLC and its counterpart DLC were not pin-compatible, thereby preventing straightforward replacement within existing hardware configurations.
IBM 486SLC
Launched in 1992, the IBM 486SLC was an upgraded iteration of the 386SLC built upon Intel’s core architecture. It incorporated a 16KB L1 cache, supported the i486 instruction set, contained approximately 1.349 million transistors, and had a die measuring 69 mm². Encased in a 100-pin BQFP, it operated with a 33 MHz FSB. Variants with clock-doubling (486SLC2 at 50 & 66 MHz) and clock-tripling (486SLC3 reaching up to 100 MHz) were also introduced. This processor delivered performance comparable to similarly clocked 486SX chips when running 16-bit applications; however, its narrow 16-bit memory bus, limited memory addressing capacity of 16 MB, and absence of an integrated floating-point unit (FPU) curtailed its efficiency under emerging 32-bit operating systems such as Windows 95.
The presence of a discrete clock-tripled 486SLC3 remains uncertain; existing specimens appear to be modified versions of other models functioning in a 16-bit mode.
IBM 486BL (Blue Lightning)
The 486BL, known as "Blue Lightning," represented a full-fledged 32-bit advancement over the earlier 486SLC. Utilizing a 0.8 μm CMOS fabrication process, this chip housed approximately 1.4 million transistors on an 82 mm² die. Released in July 1993 within a 132-pin QFP, it came in clock-doubled (486BL2) and clock-tripled (486BL3) editions running between 50 and 100 MHz. These processors were offered exclusively through IBM channels.
Subsequently, IBM introduced Blue Lightning CPUs compatible with Socket 3 based on the Cyrix Cx486 core, packaged in a 168-pin PGA format; these differed from earlier Blue Lightning models and carried "DX," "DX2," or "DX4" designations.
Due to IBM’s adoption of Cyrix cores for later Blue Lightning products, limited public documentation on initial Blue Lightning releases, and cryptic internal part numbering schemes, confusion arose within retro computing circles. Early Blue Lightning processors are frequently labeled as "486DLC" variants because of their evolutionary link to the SLC series—although IBM officially designated them as "Blue Lightning" or "486BL." The term "486DLC" originally referred to unrelated Cyrix predecessors but has persisted informally for IBM’s early Blue Lightning chips due to branding similarities.
See also
- Intel 386
- IBM PS/2
- IBM PS/ValuePoint
- IBM ThinkPad
- IBM 5x86C – utilizing the Cyrix architecture
- IBM Personal Computer