modelrail.otenko Trains, computers, vintage, retro, model railways… the lot…

NEC PC-9801VX – PK-X486 CPU Upgrade

So, this PC-9801VX came with the weird sticker on the front indicating that it was powered by a 486 CPU.

It was a pretty random claim seeing as that the base system is built from a 286. How could you possibly upgrade an 8-bit CPU to 32-bit?

A quick inspection (see the over here) saw that the 486 was contained on a daughter board which used a PLCC-socket adapter to hijack the 286 socket!

The upgrade happens to be an IO-DATA PK-X486/87SLS (IOD2Y284), consisting of a Texas Instruments TX486SLC 25mhz CPU coupled with a Cyrix FastMath CX-83387 33mhz 387 Math Coprocessor.

As that this CPU actually replaces the existing 286, it's always been active and operating the system but, regardless of this fact, the system still reports as a 286!

Trying to install DOS 6.20 very quickly throws a "You cannot install DOS 6.20 on a machine with a 286 Processor."

So, a little googling later and it turns out there's a TSR which needs to be loaded. That link indicates the TSR is named PK486.COM, but no amount of googling resulted in such a file. Instead, PK486D.COM showed better results, like this Interrupt Extender for this CPU Upgrade, but that software still didn't include the TSR!

Finally, a little more googling brought up this Japanese forum post indicating that there was an old oldsoft/98.htm page at the IODATA website that had derelique drivers. Of course, this page no longer existed, so web.archive.org to the rescue! Finally, there it is, down the bottom of the page.

Unfortunately, the files are just upgrades and want the original setup disk to hack some bytes. So, next up I started clicking random links on the iodata library site and found this page. It's full of random Win95 stuff, but one file seemed to be valid for a newer upgrade card than I had.

The COM files looked great... so I just renamed and executed... and the CPUCHK.COM even threw out the following result...

But, alas, both TSRs just reported an incorrect CPU when trying to run. Of course, what are the chances they'd even work.

UPDATE:: Adachi-san of Adachi Giken has come to the rescue! You can skip this part.

---

IF ANYONE HAS ONE OF THESE UPGRADE KITS, CAN THEY PLEASE MAKE AN IMAGE OF THE DISKS FOR THE INTERNET?... there's many sites with people asking for the software and I'd love to try it out! The box looks like this... and the disks seem to come in both 5.25 and 3.5" variants.

The disks are labelled "共通サポートソフト".

Excuse the image quality... they were flogged from a yahoo auction. But here's a better close-up...

I'll have to keep watching the auctions as those Power Up Kit /PK-X486Sシリーズ disks above went for $10.

---

The disks!

So, the kit comes with two disks: an IPL and an Installation disk.

Downloads
	IPL Disk Image		Installation Disk Image

The IPL (or Initial Program Loader) is used to boot the machine into a state where the seconday CPU is active. This is good to use prior to installation of something that needs a 386+ (i.e. DOS 6.20), so boot this disk to the following prompt:

And then swap disks. Once done, hit enter and you'll get to continue as if you booted the second disk you inserted, but on a 486! Of course, after installation, rebooting the machine will set the 286 active again and that's where the Installation disk comes in. Let the machine restart after installing DOS 6.20 and watch it crash and burn. Once it does that, insert the Installation disk and restart the machine...

That screen above scrolls onto the screen in 90s goodness... and then you get the main menu. The options are to Backup something, read the README, install the software or configure cache. Choose the third option, and then your SCSI disk.

From here, choose the partition/installation and go for it!

You'll then be told that everything is complete and that it's time to restart your machine.

With this done, your machine is now a 486! Congrats. Message me if you need the disk images.