Definitions

Intel 486DX

Intel 80486SX

The Intel's i486SX was a modified Intel 486DX microprocessor with its floating-point unit (FPU) disconnected. All early 486SX chips were actually i486DX chips with a defective FPU. If testing showed that the central processing unit was working but the FPU was defective, the FPU's power and bus connections were destroyed with a laser and the chip was sold cheaper as an SX; if the FPU worked it was sold as a DX. Computer Manufacturers that used these processors include Packard Bell, Compaq and IBM.

Back in the early 1990s it wasn't advantageous for most users to have an FPU. Those involved in heavy computer gaming or mathematical work generally benefited from the FPU. There were claims that DX chips with working FPUs were turned into SX chips to meet demand for lower-cost chips.

Some systems allowed a DX chip to be plugged into an expansion socket. A board jumper would disable the SX chip, which was hard to remove because it was inserted in a non-ZIF socket.

The FPU unit was shipped as the i487, a full blown i486DX chip with an extra pin to prevent it being used as a i486DX.

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