Problems with NexGen + Win95 programs

[feipoa]

This is a question to all those who have a NexGen system up and running - do receive an illegal operation error when running some Windows 95 programs that ordinarily work fine on, say, a 486?

For example, I've been receiving illegal operation errors when trying to open Internet Explorer 5.5, Firefox, K-Meleon, X-chat, Pirch, etc. Coincidentally those programs which require the Internet. Windows networking and shared drives work fine though. I've tried Photoshop 4&5 and GLQuake without issue. Microsoft Office 97 appears to work, but after having run it, I get an illegal operation error upon system boot-up, but closing the error, I can continue using the system as usual.

I started a thread on Vogons, https://www.vogons.org/viewtopic.php?f=46&t=64808 , but I suspect more people on the CPU-World forum have a NexGen system.

Any help/ideas appreciated. I'm guessing certain programs require instructions not present in the Nx586. Perhaps there is a list of known not working software?

[max1024]

Have you tried to install Win98? is much better in some way.

[feipoa]

No I haven't. But if you know for sure it will solve the problem, then I guess I'll have to run Win98SE.

I should also mention that the Windows NT 4.0 partition would not even start to boot. I think the issue is related to the instruction set or CPU architecture. It will take some time to fully establish which updates and software won't run properly on the Nx586.

[vmr_]

Got Windows 3.1 running on my Nexgen VLB + P90 system, did not try yet Win95 or Win98. Hope to find time in the coming weeks and test it.

[feipoa]

Thanks for your response. Looking forward to your results.

IE 5.0 seems to run fine with Win 3.11 and the NexGen on my system.

[debs3759]

When I tried setting up Windows 95 on a NexGen system, it wouldn't even install. It told me I need a 486 or higher. Can't remember what I did in the end.

[max1024]

[feipoa]

Someone mentioned to me that there is an IDON.com file that comes as part of the NexGen upgrade kit v3.1, updtpi31.exe. This utility adds microcode to the CPU detection routine to identify the CPU as CyrixInstead 486. Apparently some software has trouble detecting the CPU type. I'm not sure if this utility will help in my case, but I'm going to give it a go.

[misace]

Nexgen doesn´t have i486 and i586 instruction sets so you cannot install Win 98 or Win NT 4.0 and above. I even try it.

Long time ago I instaled (or run) Win98 lite on Am386 computer. Maybe it could work for Nexgen also. https://www.litepc.com/98lite.html This tool replace windows explorer with one from Win95 and removes lot of stuff.

[H3nrik V!]

According to the thread on vogons, you've installed Windows and then moved to the NexGen system? As many others, I would not recommend that ..

[mtx500]

I have Windows 98 SE running on both of my Nx586 PCs, one being VL and one PCI.

The important things are:
- You have to make sure your BIOS is the latest available version.
- You have to run IDON.com before Windows starts. So IDON.com must be in your AUTOEXEC.BAT file that is executed first. It's best to have it as the first line.

Note that in the BIOS Setup (pressing DEL during boot), in menu Setup > Chipset, setting "Alternate Instructions" to "yes" is not enough to get Windows 98SE installed. This setting enables the emulation of some 486 user mode instructions, but does not enable writing of EFLAGS.AC bit (Alignment Check), which some software uses to detect a 486 versus a 386 CPU.

Only IDON.com and IDOFF.com toggle both the emulation of 486 user mode instructions plus EFLAGS.AC being writeable. Of course, on a Nx586, the AC flag has no effect, but you can write it and read it back, while on a 386 you will always read 0 on that bit position.

If you don't use IDON.com, and only set alternate instructions to yes, then the Windows Explorers throws an Undefined Opcode Exception in SHLWAPI.DLL (Shell Light-weight Utility Library).

By the way, IDON.com and IDOFF.com do not itself contain any interesting code. They are just using opcode 0x0F 0x55 which is an API into the HyperCode that is stored within the BIOS chip and transferred into 2nd level cache during startup. BTW, 0x0F 0x55 is just an unused opcode that raises the Undefined Opcode Exception, so it is nothing special for the Nx586 hardware, but as all exceptions are handled in HyperCode, it is the HyperCode that treats this in a special way. So it looks like a magic NexGen-Instruction from the outside.

If your BIOS is new enough to emulate the CPUID instruction, then this instruction is always emulated. It can't be switched on/off. Some software uses CPUID to detect the CPU as 486, and some software tries EFLAGS.AC, so this explains mixed results if you have "Alternate Instructions" on but didn't use IDON.com.

But even if you do all this, there are some programs which still do not run. Some special opcode combinations are either not implemented, or not correctly implemented. The setup of Netscape 6 browser for example crashes on the lock xadd instruction. xadd is correctly emulated, but the combination with the lock prefix does not work.

[mtx500]

[vmr_]

I am also attempting a Win95 / win 98 install on Nexgen VLB system with P90, so all this info helps.

However, I am stuck with a weird primary partition size issue, as I install first DOS 6.22 and max size partition is 473mb.

BIOS seems to be at latest version.

Any tips on BIOS changes to get to 2gb partition?

Or is it more like a controller issue? Using an HDD emulator with SD card...

Note: BIOS does support Logical Block Addressing (LBA), will activate and see if it enables usage of large drives. Getting used with the 486 era systems

[mtx500]

Follow these steps in BIOS setup:

1) If your hard disk has an option (jumper) to limit the number of heads to 15, you should use this option.
2) in Setup > Peripheral at Primary, set the options Block Mode, 32-Bit Transfer, and LBA Mode to yes.
3) in Utility, click DetectMaster and accept
4) if your hard disk does not have that option to limit the number of heads: go to Setup > Standard > Master Disk and make sure that the number of Heads is not 16. If it is 16, change that to 15, thereby wasting 1/16 of the disk capacity. This should not be a problem for a historic machine.

The NexGen BIOS has a bug (that most of the BIOSes at that time had): The number of heads is stored in only 4 bits. The value 1 means 1 head, 15 means 15 heads and 0 means 16 heads. This has to be treated specially, and BIOSes that do not, end up multiplying and dividing by zero instead of 16. And division by 0 raises an exception, crashing the machine during the boot process.

[feipoa]

mtx500 - thank you very much for this information.

I had no idea what Alternate Instructions was for. The manual doesn't go into any detail aside from "This option should be set to OFF for normal operation." I will try setting it ON.

If I am using IDON.com, do I still need to set Alternate Instructions to ON in the BIOS?

The BIOS I have been using the same same one which appears in the upgrade kit v3.1, that is, P06y034Q. Is there a newer or modified one which will do what IDON.com does?

With using Alternate Instructions and IDON.com on your PF-series NexGen, which software were you still unable to get working (aside from Netscape 6)? Does IE 5.5 work?

Sounds like NT 4.0 is out. I looked on ePay for an NT 3.51 workstation full version disc and they all appear to be gone. That is, aside from a sealed box kit for $500 and a 3.51 upgrade disc for $30, which according to the box, requires you have version 3.5 as well.


vmr_ - Have you tried using a SCSI add-on card? If I recall right, I can use 8 GB partitions with my Adaptec AVA-2825.