A version of Intel's 486DX processor with power saving enhancements. Its core voltage is 3.3 V, while most x86 CPUs of the time used 5 V. In addition, it has some power management instructions, including those for lowered clock frequency and suspend mode. These can be controlled by the machine's BIOS, or possibly by the operating system as well.

The SL has all the features of 486DX, and should not be confused with 486SX; the low-power version of 486SX is called 486SL-NM.

Sources: my old AST laptop has one of these. See also the following sites:
  • http://wombat.doc.ic.ac.uk/foldoc/foldoc.cgi?486
  • http://www.pcguide.com/ref/cpu/char/powerPM-c.html