Socket 1-3 Motherboards
Socket 1 was the second of a series of standard CPU sockets created by Intel into which various x86 microprocessors were inserted. It was an upgrade to Intel's first standard pin grid array (PGA) socket and the first with an official designation. Socket 1 was intended as a 486 upgrade socket, and added one extra pin to prevent upgrade chips from being inserted incorrectly. It was a 169-pin low insertion force (LIF) 17×17 pin grid array (PGA) socket suitable for the 5-volt, 16 to 33 MHz 486 SX, 486 DX, 486 DX2 and 486 OverDrive processors. The Pentium OverDrive will not fit into Socket 1 because it has four rows of pins and the socket only has three.
Socket 2 added support for Pentium OverDrive processors, although by the time the POD was released in 1996 the specifications had changed breaking compatibility with socket 2 motherboards. It was a 238-pin low insertion force (LIF) or zero insertion force (ZIF) 19×19 pin grid array (PGA) socket suitable for the 5-volt, 25 to 50 MHz 486 SX, 486 DX, 486 DX2, 486 DX4, 486 OverDrive and 63 or 83 MHz Pentium OverDrive processors.
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.
Today: These days Socket 3 motherboards are a good basis for a retro rig. A wide variety of CPU's will work in them, though compatibility is highly dependent on what exact motherboard you are planning to use. There are basically 2 choices (3 if you count the 486 motherboards with only ISA slots), either go PCI for the added benefit of having a wide variety of expansion cards to choose from, or go VLB for that added retro-feel. 486 motherboards are one of the trickiest to setup though and can be very frustrating at times as there are a lot of possible hurdles. The BIOS battery may be empty or has started to leak, the correct jumper settings may be unknown (due to not having any type of manual), even finding a suitable case may be difficult due to the age of these systems. And on top of that, the parts for a 486 can be rather expensive to purchase, but it can be all that more rewarding once it's finally up and running.
- ETEQ ET6000 "Cheetah"
- ETEQ ET9000 "Jaguar" single chip
- OPTi 82C481/482 "HiB chipset", WriteThru
- OPTi 82C491 WriteBack
- OPTi 82C493 WriteBack
- OPTi 82C495SLC/206Q, Write Back (2 chip, unbuffered VLB)
- OPTi 82C495SX/392SX/206Q, Write Back (3 chip, buffered VLB for improved compatibility but slower performance)
- OPTi 82C495XLC/206Q, Write Back (2 chip)
- OPTi 82C496[A,B]/497/206 (2 or 3 chip, 497 is optional cache controller)
- OPTi 82C571/82C572 VLB, ISA "486/Pentium Writeback" (Hybrid 486/586 design, 64-bit SRAM, 32-bit DRAM)*SiS 401/402 ISA
- OPTi 82C682, 386/486WB EISA chipset
- OPTi 82C683, 386/486AWB EISA chipset
- OPTi 82C802G ISA,VLB (single chip version of 82C895)
- OPTi 82C895/82C206 ISA,VLB
- SiS 406/411 EISA, VLB
- SiS 460 ???
- SiS 461 ISA, VLB
- SiS 471 ISA, VLB
- SiS 496/497 ISA, VLB, PCI
- Symphony "Haydn"
- UMC UM82C491/82C493 ISA,VLB
- UMC UM8496/8498 ISA, VLB
- UMC UM8881/8886 ISA, VLB, PCI
- VIA VT82C496/82C505/82C406 ISA, VLB, PCI