PC-98 vs. IBM PC Video Research & Questions

[RobIvy64]

Hey guys,

I've been working on a video about the NEC PC-98 for a few weeks now. One part of my script I have yet to finish is the detailed information on why the PC-98 is not fully IBM compatible, and some of the key differences from a software perspective.

Can anyone provide some insight on this? I know *some* PC software will work on the PC-98, but most will not. I'd like to briefly demonstrate why this is.

[kobushi]

It might make sense to talk first about why IBM PC-compatibles and the PC-9801 series are similar, before moving on to the differences.

Like the IBM PC, the PC-9801 uses a CPU that supports the x86 instruction set. Early pc-9801 models were equipped with intel-compatible chips designed by NEC (like the V30), but after a time intel chips like the 286/386/486/Pentium/Celeron were used instead.

The pc-9801 also runs MS-DOS, but it's not exactly the same as the MS-DOS in the West. PC-9801 MS-DOS is essentially a modified port of IBM PC-compatible MS-DOS.

Combined together, an Intel(-ish) CPU and a Microsoft(-ish) OS mean that the PC-9801 can read and execute IBM PC-compatible software to a degree, and many basic command-line utilities will work fine on either system.

But beyond that very basic level of compatibility, the machines are really quite different.

- BIOS, port addresses, memory map are all different
- PC-9801 used C-bus, a 16-bit data bus designed by NEC. IBM PCs of the 80s and 90s used a mix of 8-bit and 16-bit ISA buses before being replaced with PCI.
- Hard disks use a different type of partition table
- Drive letters are assigned differently. On an IBM PC, the floppy drives are A: and B: while the first hard disk is C:. On a PC-9801, A: is always the drive you booted from.
- PC-9801 graphics subsystem is completely different than Western CGA/EGA/VGA standards. Ordinary PC-9801 output is 640x400, 16 colors, 56Hz refresh, 24kHz horizontal frequency.
- PC-9801 used a built-in kanji rom chip for Japanese text display. IBM PCs outside Japan obviously lack this chip, so PC-9801 programs with Japanese text will not display correctly on an IBM PC.

Essentially, the only cross-compatible programs are the ones that never leave the realm of the CPU, like simple command-line programs. Anything that goes beyond the most basic I/O will crash and burn.

Starting with Windows 95, the OS abstracted away enough of the underlying hardware so that software built for Windows 95 will essentially run on any computer running Windows 95. However, because they need to interface with the underlying hardware in different ways, Win9x for IBM PCs and Win9x for PC98 are quite different, and Japanese Win9x CDs include separate builds for IBM PC and PC-9801.

[RobIvy64]

Perfect, that is exactly what I was looking for, thanks!

I have the similarities documented, but wasn't very clear on the key differences.

[cuba200611]

And of course, don't forget the sound differences: Both PC-98s and IBM compatibles only had a PC speaker during their early days - but from there they diverge.

History of most common PC compatible sound hardware:

• 1981: 1-channel PC speaker, produces a pulse wave (however it is possible to force samples out of it)
• 1983: (PCjr / Tandy 1000 only) One TI SN76489 (3 channels pulse, 1 channel noise; same chip used in the Master System)
• 1986: The Covox Speech Thing, which was a DAC connected to the parallel port
• 1987: The Adlib with a single YM3812 FM synth (9 channels or 6 with 5 perc channels; 4 waveforms)
• Also in 1987: The Roland MT-32 (32 channels LA synthesis) connected via MIDI to an MPU-401 card (of which there was a variant for the PC-98)
• 1989: The Soundblaster (Same as the Adlib, except with the ability to play samples)
• 1991: General MIDI (Nuff' said)
• 1992: The Soundblaster 16 which has an YMF262 (enhanced YM3812) and increased fidelity in playing samples (It also had a variant released for the PC-98)

History of most common PC-98 sound hardware:

• 1985: the PC-9801-26 (most PC-98 sound boards were made by NEC, and have the PC-9801 prefix) which has an YM2203 (3 channels FM [sine only] and an YM2419 (AY-compatible chip; used in many arcade machine and computers such as the Atari ST) built in)
• 1992: the 86, which has an YM2608 (same as the YM2203, but with 3 more FM channels, an PCM channel to play samples, and 6 perc channels [the YM2612, used in the Mega Drive/Genesis, is the same chip, but with only the FM channels and some other modifications, such as being able to play samples off the 6th channel.])

[kamiboy]

New video on the PC-98, eh? Looking forward to it. There is very little english language material covering the deepest end of Japanese vintage PC's. The few that exist are often not very well produced, so you are doing god's work son.

[98digger]

Can't wait to see your new PC-98 video when it's finished!   

As a more visual demonstration of why the PC-98 and IBM PC are incompatible with each-other, I recommend showing what happens when you run an IBM PC program on a PC-98 (typically it results in a "crash" screen) and vise-versa. Don't try doing it on real hardware though; an incompatible program could potentially cause damage to the system, so do it in T98 Next. In particular, attempting to run the OpenGEM desktop and FastTracker in T98 yields some interesting results. 

Also, regarding the difference between the IBM PC and PC-98, it might be a good idea to draw a comparison to the difference between, say, the Amiga and 68k Macintosh. Like the PC-98 and IBM PC, both of those systems use the same type of CPU (Motorola 68000), yet are incompatible with each other.

Good luck with your video, 
-98digger

[SkyeWelse]

Thanks for the information about the similarities and differences Kobushi. If you don't mind, would it be okay for me to use some of this for information cards for the PC-98 machines I plan to exhibit at the upcoming Atlanta Vintage Computer Festival next week? This information really couldn't have come at a better time!

I'm also looking forward to Rob's next video. I'll be starting up a Youtube series soon that covers PC-98 tutorials and MSX hardware / software as well soon. I've just hit a snag on some of the video editing recently. I do have a video that is ready to go pretty much that covers how to turn a Gotek into a HxC from start to finish at least.

Edit: Looking through your list again Kobushi, I thought I should add that there were differences between the disk drive hardware as well. Most disks were 620K / 1.20K format, and later the 1.44K format was adopted, as well as 720K I believe in some drives though I could be wrong. The PC-98 3-Mode drives were unique to the PC-98 hardware and were not compatible with IBM PC/AT Floppy Drives, and vice versa. When I blew a chip on one of my original PC-98 3.5" FDD drives, I managed to find the exact same model of the drive being sold on eBay, even got two of them, but I discovered the hard way that while they were the same model number, it was a version sold outside of Japan and designed for PC/AT and not for PC-98. I was able to at least read 1.44K formatted disks, (possibly even write to it though I didn't try) but I could not read a 620K / 1.20K formatted disk.


-Thomas

[kobushi]

would it be okay for me to use some of this for information cards for the PC-98 machines I plan to exhibit at the upcoming Atlanta Vintage Computer Festival next week?

Sure no problem!

The floppy drives are good to note as well. It's complicated, because the floppy drives vary among different PC98 models too. IIRC, the 3.5" drives on my old PC-9801UX were incompatible with the PC-9821 series. Hardware nuances aside, the most common PC98 floppy format was 1.23MB 2HD@360rpm (1024 bytes x 8 sectors x 154 tracks = 1261568 bytes), which is the same format used in the FM Towns and the X68.

I'm looking forward to everyone's videos.

[RobIvy64]

Just finished mine.

https://www.youtube.com/watch?v=HLODzv2Wnws

Thanks for the technical clarification, Kobushi! I did see some of that while slogging through Japanese sites, but it's nice to hear from an expert.

[kobushi]

Great video! Very fun and informative. I'm glad you showed people that the PC-98 has other games besides hentai and Touhou (although people might be in for a surprise when they play Briganty...)

If you don't mind a small correction, early in the video you said that NEC announced their entry into the home computer market in 1980, but this is incorrect. NEC got in on the ground floor, first releasing a DIY computer kit called the TK-80 in 1976. Then they released the PC-8001 in 1979, which was successful and paved the way for the massively popular PC-8801.

That 99% quote from Tramiel is really interesting though. I think it must be referring to the PC-8001. The American versions of the PET-2001 would have been available in Japan almost immediately in 1977 and 1978 through import shops, but at some point (early 1979 maybe?) Commodore established the Commodore Japan subsidiary to market a localized version of the PET with the Japanese keyboard shown in your video.

[RobIvy64]

Thanks Kobushi! I realized this shortly after releasing the video and have already corrected it. I had completely forgotten about the PC-8001