IBM 386SLC

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IBM 386SLC: a budget, licensed version of Intel’s 386SX released in 1991. It has a 32-bit internal data path, 16-bit external bus, and 24-bit memory addressing, plus power management and an 8 KB cache. These features let it run at 386DX-like speeds for less money. IBM called it the “Super Little Chip” and it powered the PS/2 35, 40, and 56 series and the PS/ValuePoint 325T, but it never gained wide market share. A key reason was an Intel licensing rule that IBM could only sell CPUs as part of a system or upgrade board, though it was marketed as an upgrade for 8086 PS/2 25 Series machines.

The 386SLC was built with CMOS technology on a 161 mm² die and came in 16, 20, and 25 MHz versions; the 25 MHz model used only 2.5 watts, making it suitable for laptops. Although the SLC (and later the DLC) was bus-compatible with i386SX/DX, it was not pin-compatible, so it couldn’t be a drop-in replacement.

IBM later introduced the 486SLC, an improved 32-bit version based on Intel’s core, with 16 KB of L1 cache and an i486 instruction set. It used about 1.349 million transistors on a 69 mm² die and appeared in clock-doubled (SLC2) and clock-tripled (SLC3) forms, up to 100 MHz. While faster in some tasks, it shared the era’s drawbacks—limited memory addressing and no on-chip FPU—making it less suitable for 32-bit OSes like Windows 95. IBM also produced the 486BL family (fully 32-bit) and later Socket 3 Blue Lightning 486 CPUs based on Cyrix cores, which led to naming confusion in the market.