Socket 1-3 Motherboards
Socket 1
Socket 2
Socket 3
Socket 3 was the successor to Socket 2 and officially supported 3.3V CPU's in addition to the older 5V CPU's (even though not all Socket 3 motherboards did in fact support 3.3V CPU's). It was also one of the first CPU sockets that came in a Zero Insertion Force form, though some Socket 2 ZIF sockets were made (Socket 2 usually came in a High Insertion Force form). Socket 3 was also the first CPU socket to come with tabs on it's sides for use when installing a CPU cooler. Many Socket 3 sockets have these tabs missing though and the only way to install a CPU cooler is to mount it directly onto the CPU. Some Socket 3 CPU's were sold with pre-installed heatsinks though. Socket 3 was also the last CPU socket where it was possible to fit the CPU in 4 different ways physically because the pinout of the CPU's in that time were symmetrical, so care and attention is needed when installing any 486 CPU. The Pentium Overdrive for Socket 3 however had a couple pins missing in 1 corner and thus could only be installed the correct way. Installing a 486 CPU in the wrong orientation may result in damaged components.
Socket 3 motherboards support a wide variety of CPU's ranging from the lowly 16MHz 486SX all the way to the Pentium Overdrive (which ran at either 63MHz or 83MHz), the Cyrix 5x86 (which usually ran at 100MHz though 120MHz and 133MHz samples exist) and the AMD 5x86 (which ran at 133MHz though 150MHz and 160MHz examples exist). It offers good flexibility because of the wide range of CPU's supported, though 486 motherboards are typically the trickiest to setup partly because of the large amount of jumpers. Also finding a manual for any given board could prove to be quite a task in itself.
Socket 3 motherboards exist with either VLB slots or PCI slots or a mix of both. The motherboards with both VLB and PCI slots usually have 1 bus bridged to the other, resulting in slow performance of the bridged bus. All Socket 3 motherboards have ISA slots though.
Most Socket 3 motherboards came with 2 to 4 32-bit memory slots which supported FPM memory modules. Only the very latest Socket 3 motherboards will work with EDO memory. Some of the earliest Socket 3 motherboards also used the older 8-bit memory slots, of which 4 identical modules needed to be fitted.
Socket 3 motherboards were one of the last motherboards that used upgradeable cache modules (later boards often used cache modules directly soldered to the motherboard, making an upgrade or replacement of defective modules virtually impossible). When new, Socket 3 motherboards were typically fitted with either 128KB or 256KB cache. Some motherboards however can be upgraded to 512KB or even 1MB of cache, which results in a larger cacheable area.
Typically Socket 3 motherboards used a FSB of 16MHz to around 50MHz with 33MHz FSB being a sweetspot as a higher FSB could increase the chance of system instability (particularly in PCI motherboards that don't have a divider) and could cause other problems like not being able to install 2 or 3 VLB cards in the same motherboard.
Even though Socket 3 motherboards with PCI slots exist, it's PCI implementation was still in it's infancy.
And even though 33MHz FSB was typical and 40MHz and 50MHz often officially supported, many manufacturers of later Socket 3 boards had undocumented FSB settings that could make it possible to increase the FSB even more. Some Socket 3 motherboards turned out to have jumper settings for 60MHz and even a 66MHz FSB. That combined with a PCI divider could in theory result in vast overclocks with 200MHz having been reached by several people using AMD 5x86 CPU's.
All Socket 3 motherboards were made using the AT style form factor (or a proprietary design). No ATX 486 motherboards were ever made.
