The 486 SX is one
example of a typical
Intel marketing ploy: arificially disable or
dumb down a
CPU for the sole purpose entering another
price point.
It started with the 386 SX. This was just a 386 DX with its external bus stepped down to 16 bits (unlike 32 bits for the 386 DX). The 486 SX is exactly the same as the 486 DX, but with the FPU disabled. Several years later, the first Celerons arrived, which were simply Pentium IIs with no L2 cache.
Today, it still goes on. The newest Celerons, with 128 Kb of on-die L2, are the exact same silicon as the current Pentium !!!s, but with half of the L2 cache disabled.