Intel 80486SX
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The Intel 80486SX is an Intel 486DX microprocessor with its floating-point unit (FPU) disconnected. All early 486SX chips were actually 486DX 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. Some have claimed 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 Intel 80487, a full blown 486DX chip with an extra pin to prevent it being used as a 486DX.
References
- This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
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