For sale is a rather rare I-O Data PK-X486S50-3 upgrade card for PC-9801 series computers, that will also likely function in Tandy 1000 systems. Somewhat similar to the Make-it-486 type card. Card features a IBM SLC2 at 50MHz, 16KB CPU cache memory and Cyrix coprocessor (either Cx87SLC-25 or Cx87DLC-33). Will fit into the TL, TL/2 or TL/3 mainboards. There are four dipswitches: switches 1 enables and disables the math coprocessor. The other switches are not used.

I can send PDF link to drivers, such as as the PK-486S50 Enable cache tool (also available on GitHub), the IBM486 cache driver, and original I-O DATA “Power Up Kit / PK-X486S” series drivers disk image. Everything is in Japanese and please confirm compatibility with your particular system.

Please carefully check compatibility with your system.

Fast shipping from Tokyo, Japan. Please be aware of customs import fees in your country, however this falls within the duty free allowance for the U.S. and no import duties are likely due. Also be aware of possible customs processing delays, particularly in the E.U.

So is it bottlenecked by the 16 bit 386sx interface?

on ebay there are 286 to 486 upgrade, both the cyrix 486slc with 1k cache and 486SLC2 running at 66 MHz with 16kb. good upgrade for a 286 pc like Tandy 1000 its all in Japanese though, and needs a driver also in Japanese.

so its pipelined and 1 instruction per clock. does it need a heatsink and fan?

I have a blog post about the 486SLC2 (there’s a search bar in the top right). When running at 66 MHz, it could keep pace with a regular Intel or AMD 486 running at 33 MHz. At 50 MHz, it felt more like a 25 MHz Intel.

486SLC2: 16Kb cache, clock-multiplied (2x), supports all Intel 486SX instructions

okay is it pipeline with 1 instruction per cycle so on par with intel 486 at same clock ?

The IBM SLC CPUs (derived from a licensed Intel 386SX codemask, 16-bit data bus, 24-bit address bus):

386SLC: 8Kb cache, not clock-multiplied, supports all Intel 486SX instructions
486SLC2: 16Kb cache, clock-multiplied (2x), supports all Intel 486SX instructions
486SLC3: 16Kb cache, clock-multiplied (3x), supports all Intel 486SX instructions

The IBM DLC CPUs (derived from a licensed Intel 386SX codemask, 32-bit data bus, 32-bit address bus):

486DLC2/486BL2 (“Blue Lightning”): 16Kb cache, clock-multiplied (2x), supports all 486SX instructions

cyrix calls their 486, but it uses the 386 socket and bus, and only has 1 kb cache and no math coprocessor.

are they also pipelined and can do 1 instruction per clock cycle, i.e 33mhz = 33 mips, or about twice performance at same clock as a 386?

i know it won’t be 100% of a real 486 but perhaps 80%, or one and a half times faster than a 386 at same CPU?

IBM 486SLC2 has up to 16k cache, but apparently is a 386sx but with 486 compatible instructions.