The Intel 386 SX CPU quickly replaced the 286 CPU in the early 1990s. For a time, it was a very popular CPU, especially for people who were wanting to run Microsoft Windows. Yet the two CPUs run at nearly identical speed. So what was the big deal? The 286 vs 386SX argument could be confusing in 1991, and it’s not much clearer today.
Half a 386DX
From a software point of view, the 386SX was the same chip as its older and more expensive brother. But unlike the DX, it had a 16-bit memory bus. That meant it accessed memory at about half the speed. Sometimes worse, because a good DX board had Level 2 cache, which was something most SX boards lacked.
The predecessor, the 286, also had a 16-bit memory bus. The 286 and 386SX were the budget CPUs of the early 90s, the equivalent of today’s Core i3 at best.
When running DOS software, there’s almost no difference in speed between a 286 and a 386SX running at the same clock speed. Sometimes the 286 will be faster.
The appeal in the early ’90s was basically that an SX gave you access to 386 software while costing almost the same as a 286.
The other advantage, over time, was that the clock speeds didn’t stay the same. The 286 topped out at 25 MHz, and the 20 and 25 MHz versions were not exactly common. You could get them, but it was easier to find an SX. Intel produced SX chips at up to 33 MHz, and AMD took it to 40 MHz.
The reason for the SX
The main reason the SX existed was Microsoft Windows. Windows would run on a 286, but not in 386 enhanced mode. That meant no multitasking DOS programs, and no virtual memory. Windows ran better on a 386DX or a 486 system, but those were expensive in the very early 1990s. The SX provided something better than a 286 at about the same price. If you only ran DOS software and weren’t interested in multitasking, you wouldn’t notice much difference, aside from better memory management. But if you wanted to use Windows, it was better. Still not great, but better.
So a fair few 286’s received motherboard swaps in the early nineties. Though not a tremendous upgrade, upgraders likely got a slight clock speed boost, better multitasking, and the ability to use more memory, since most 286 boards topped out at 4MB or even 1MB, versus 16MB for a 386sx. Few people ever upgraded their 386SXs that far, but they liked having the option.
Windows’ popularity killed the 286, and fast. In August 1991, the 286 accounted for 40% of new computer sales. It took three months to drop to a paltry 15 percent.
Cynically, I think there was one more reason. Intel had to license the 286 to other companies. They didn’t license the 386. I think they produced the 386SX to displace those second-source 286s. AMD developed its own 386, but by that time, Intel was ready to cut prices on the 486 to stay a step ahead. The 286 vs 386sx mattered more in advertising than in the real world.
That’s why the 386SX had a pretty short shelf life. Once AMD had 386 chips to sell, Intel cut prices on 486s. But for a couple of years it served a purpose. And the chip lived on as a budget option for a couple of more years. There were lots of chipsets for it in the supply chain, and I remember being able to buy new 386SX motherboards cheaply into early 1995. While outmoded at that point, those boards were useful for repairing existing systems that just ran DOS. I could get a board for less than $200 and swap it into a malfunctioning system in 30 minutes. If you find SX boards in old systems that didn’t originally come with them, that may be why.
A 286 vs 386sx today
So which is a better hobbyist retro rig today?
All things being equal, the SX. Any early 90s software that runs too fast on a 486 will run about as well on an SX as it would on a 286, especially if the SX has a turbo switch. And a 386SX-33 is an ideal speed for some popular titles, notably Wing Commander.
The SX won’t fight you as much on memory management and the drivers for everything you want will work on an SX. Getting 16-bit sound cards working on a 286 is possible, but takes more doing than it needs to. You may run into similar issues with network cards. There’s just a lot more out there designed for the 386 than the 286.
Don’t get me wrong. I enjoy my 286, but if it were my only retro PC, I probably wouldn’t be as fond of it.
Trivia: anyone remember the “Red X” campaign and the resulting 386SX shortages which lasted until 1991 or so? Many chipsets was designed to support both.
I’ll quibble with the remark that motherboard upgraders only got a “slight” clock speed upgrade when switching from a 286 to a 386sx. Almost any increase in clock speed across otherwise comparable systems could have a significant impact on performance in those days. For example, the improvement between a 25 MHz 286 and a 33 MHz 386sx could be around 30%, despite a mere 8 MHz clock speed difference.