Cyrix Cx486DLC

Cyrix Cx486DLC Microprocessor
Cyrix Cx486DRx² Microprocessor.

The Cyrix Cx486DLC was an early 486 CPU from Cyrix, intended to compete with the Intel 486SX and DX. Texas Instruments, who manufactured the 486DLC for Cyrix, later released its own version of the chip, the TI486SXL with 8kB internal cache vs 1kB of the original Cyrix design. The similarly named IBM 486DLC, 486DLC2, 486DLC3 (aka Blue Lightning) are often confused with the Cyrix chips, but are not related and instead based on Intel's i486 design.

Introduced in June 1992, like the later and more famous Cyrix Cx5x86 it was a hybrid CPU, incorporating features of a new CPU (in this case the Intel 80486) while plugging into its predecessor's (386DX) socket. It ran at speeds of 25, 33, and 40 MHz.

The 486DLC can be described as a 386DX with the 486 instruction set and 1K of onboard L1 cache added. Because it used the 386DX bus (unlike its 16-bit cousin, the 486SLC) it was a fully 32-bit chip. Like the 386 and 486SX, it had no on-board math coprocessor, but unlike the 486SX, it could make use of an Intel 387DX or compatible numeric coprocessor. A few 486SX motherboards also provided i387 sockets, but this feature was a very much a rarity. Due to the smaller L1 cache, the 486DLC could not compete on a clock-for-clock basis with the 486SX, but a 33 MHz 486DLC could keep pace with a 25 MHz 486SX, cost less, and offered the ability to upgrade further with the addition of an inexpensive math coprocessor.

While some advertisements in PC magazines from smaller manufacturers touted the superiority of their 486DLC over name-brand computers sporting a 486SX, in reality the only advantage the 486DLC offered feature-wise over the 486SX was the ability to add an inexpensive math-coprocessor. The Intel 487 "math coprocessor" for 486SX users was in reality a CPU replacement—a 486DX with a different pinout—and originally cost several hundred dollars more than a 387.

As prices on Intel's 486 line fell, Cyrix found it more and more difficult for its 486SLC and DLC CPUs to compete and had to release a fully pin-compatible version of the 486SX and DX in 1993.

The 486DLC did not see widespread use among large OEMs, but it was widely known among the hardware enthusiast community that an AMD 386DX-40 or Cyrix 486DLC-33 could keep up with a 486SX-25 at a lower cost, so it gained a small following among budget-minded enthusiasts. It was also sometimes used as a replacement for a 386 CPU to give a small speed boost. However, the 486DLC was not designed to be a direct CPU replacement and could lead to stability problems in older boards it was not intended for. Cyrix later released a clock-doubled "direct replacement" upgrade chip for 386DX systems called the Cx486DRx2.


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