P24T = pentium overdrive (POD5V) - basically a pentium for the 486 socket. Comes in 63 and 83MHz flavors.
P24D = intel 486 overdrive - a DX2 that runs at 5v, designed for older socket 1 motherboards. Full name is i486DX2WB
m6 = a cyrix 486 DX. Full name Cx486S. Comes in 33 or 40MHz flavors.
m7 = a cyrix 486 DX2. Comes in speeds of 40 to 80MHz.
umc 486 - exactly that - a 486 made by UMC.
amd 486 - self explanatory - a 486 made by AMD. They sometimes need different jumper settings then intel DX4 chips since most come with 8kb of write trough L1 cache, but write back versions exist.
DXL - 486 made by amd. Full name is A80486DXL
The 486DX is your garden variaty 486, usually running at 33MHz, but 50MHz versions exist. They are not clock doubled (no multiplier, they run at FSB speed).
The 486DX2 runs at FSB x2. For 33MHz fsb you get 66MHz. Intel made 50 (25x2) and 66Mhz (33x2) versions. Some chips run at 5v, others at 3.3v. AMD and cyrix made 50, 66 and 80MHz versions.
The DX4 runs at FSB x3. The 100MHz intel DX4 runs at 33x3 (100MHz), and so does the cyrix 586-100 and the AMD DX4-100. AMD also made DX4-120 chips that run at 40x3.
586 chips run at 4xFSB (for the AMD 586-133 - 33x4) 3xFSB for the cyrix/ibm 100 and 120Mhz chips (33 or 40 x3) or 2xFSB for some IBM chips (made by cyrix) witch run at 66x2.
To correctly set up a 486 (or pentium / AMD K6 / Cyrix 686 socket 5 or socket 7) cpu, you need to know about the following:
1. CPU voltage - early 486 chips run at 5V. Later chips run at 3.3 or 3.45v (older mainboards only support 5v). Some Cyrix DX2 chips run at 4V. Some (rare) cyrix 586 chips run at 3.65 or 3.7v. Socket 5 pentiums run at 3.3v, while socket 5 AMD k5 chips run at 3.45v. Socket 7 CPUs run on dual-voltage - 3.3v for the I/O, and 2.8v for the CPU core in the case of pentium MMX chips. AMD K6-2 chips run at 2.2, 2.3 or 2.4 volts. Cyrix chips run at 2.3 or 2.9 volts.
2. Front side bus frequency. Usually 33MHz for most 486 chips - so a 100MHz 486 DX4 runs at 33MHz x 3 = 100MHz. A 80MHz AMD or Cyrix DX2 runs at 40MHz x 2 = 80MHz. Pentium chips run at 50, 60 or 66MHz. a 133Mhz pentium 1 runs at 66x2. K6-2 chips run at 66 or 100Mhz - so a 400MHz CPU is 100MHz x 4 or 66MHz x 6.
3. Multiplier. For 486DX chips running at 25, 33 and 50Mhz, there is no multiplier - they run at FSB speed. DX2 chips however have a 2x multiplier. DX4 chips have a 3x multiplier, and some 586 chips like the am5x86-p75 running at 133MHz has a 4x multiplier - however - there is no 4x setting on any 486 board - 4x capable chips interpret 2x multiplier setting as 4x.
4. Cache mode - this tells the motherboard to run the CPUs L1 cache in write back (faster) or write trough mode. Some CPUs only support write trough mode.
To set up a CPU, chose the correct voltage (written on the chip) via jumpers. Then set the FSB speed (usually 33MHz) - different jumpers and then set the multiplier (also by jumpers).