For sale is a rare I-O DATA PK-X486S50-3 CPU accelerator board for compatible NEC PC-9801 computers.
The PK-X486S50-3 upgrades supported systems with an IBM 486SLC2 processor running at 50 MHz, together with 16 KB of onboard CPU cache and an integrated Cyrix Cx87DLC-33 math coprocessor. According to I-O DATA documentation, it is designed for compatible PC-9801 RX, DX, UX, EX, and VX series computers.
Although originally intended for NEC PC-9801 systems, the PK-X486S50-3 has also become well known among vintage PC enthusiasts for use in certain Tandy 1000 systems. Community reports indicate compatibility with models such as the Tandy 1000 TL, TL/2, and TL/3, although compatibility outside the intended PC-9801 platform is unofficial and may require additional software or configuration.
The board features a four-position DIP switch block. Switch 1 enables or disables the integrated math coprocessor, while the remaining switches are largely undocumented in the original manual. Enthusiasts have reported that some software drivers can also enable the processor cache and higher operating modes on compatible systems.

I can provide HFE disk images of the installation/support software (PK-X486S-INST and PK-X486S-IPL) to the buyer upon request after purchase.

Cosmetic condition is excellent overall. The PCB is clean, components are intact, and the board presents very well. Please review the photos carefully for the exact item and cosmetic condition.
As with all vintage computer hardware, compatibility depends on the host system and software configuration. Please verify compatibility with your intended machine before purchasing.🇺🇸 US buyers: shipments are sent DDP (Delivered Duty Paid), which means there are no duty fees on delivery, as duties are included in the shipping rate.
Please also note that customs delays may occur, particularly within the EU.
This is vintage hardware/software for vintage computers. Use of this item requires era-appropriate knowledge and compatible hardware/software. Please carefully verify your intended use and compatibility before purchasing. I am happy to answer reasonable questions, but compatibility with every system or configuration cannot be guaranteed, and step-by-step installation support is not provided. Issues arising from incorrect installation, modification, or incompatible use are outside the seller’s responsibility.
I usually ship within 24 hours. If shipping falls on a Saturday in Japan, dispatch may occur the following Monday.