I486SX

Lore & Background

In the early 1990s, common applications such as word processors and databases did not benefit from an FPU, while CAD applications did. AMD had begun manufacturing a faster clone of Intel's i386DX, the Am386. In response, Intel wanted to provide a lower-cost i486 CPU for system integrators without sacrificing profit margins. The i486SX was introduced in mid-1991 at 20 MHz with 8 KB of cache in a PGA package. The first revisions were practically identical to the i486 but with the FPU internally disabled. Later versions from 1992 onward had the FPU entirely removed for cost-cutting reasons and came in surface-mount packages as well. The first computer system to ship with an i486SX from the factory was Advanced Logic Research's Business VEISA 486/20SX in April 1991. Initial reviews were generally poor, with the chip deemed an example of crippleware.

Reader's Guide

The i486SX allowed system integrators to offer a lower-cost entry point into the i486 line while Intel maintained higher margins on the full i486DX. Its significance lies in the upgrade path: many systems allowed users to upgrade to a CPU with the FPU enabled via the i487, which was actually a full i486DX chip with an extra pin for keying. The i487 would take over functionality, rendering the original i486SX inactive. The original chip was left in place because it was physically hard to remove, often being soldered or in non-ZIF sockets. Later i486 OverDrive processors plugged into the 169-pin socket (Socket 1) and offered further performance enhancements. The i486SX demonstrated a market strategy of segmenting a product line by disabling a feature, a practice that drew criticism but proved commercially viable.

Did You Know?

• The i486SX was priced at US$258 at introduction.
• The i486SX could perform up to 20 MIPS at 25 MHz.
• Low-power versions were available at 16, 20, and 25 MHz.