The designation of CPU speed for a 486. The second number is the clock rate: 486/50 means 50 MHz. CPUs beyond 33 MHz may have different internal and external speeds as noted in the following table. The internal clock speed is the rate at which the CPU processes (calculates, compares, etc.). The external clock speed is the rate at which it communicates with RAM and external bus.

     486 Type      Internal     External
     486/25        25 MHz        25 MHz
     486/33        33 MHz        33 MHz
     486/50        50 MHz        50 MHz
     486/50DX2     50 MHz        25 MHz
     486/66        66 MHz        33 MHz
     DX4/75        75 MHz        25 MHz
     DX4/100      100 MHz        33 MHz