VOGONS


Nexgen - the 486 killer - WIP

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First post, by mpe

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Let's build an unusual mid-90 DOS system 😊

First the case:

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Yes, It is an ATX case, but it is new, roomy and IMHO it is quite tasteful for a retro system.

Now the motherboard. AFAIK there are only two possible motherboard types and this Alaris NxVL is the one I have. So it was an easy choice:

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The Nx586-P90 is the most common NexGen CPU model. Clearly better than almost any 486, but not quite at Pentium level. But no FPU 😲 And again the only option for me.

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Given by the VL-Bus architecture and focus on DOS, the VGA is a clear choice. Hercules made Tseng ET4000/w32p is my favourite VLB card ever made. It is 32bit, but 2MB of interleaved memory gives it effective 64bit speed. With 45ns RAM chips It performs just as well as it looks:

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Last edited by mpe on 2019-10-12, 13:21. Edited 4 times in total.

Dependency Injection Blog||486DX-50 EISA|NexGen Nx586

Reply 2 of 48, by mpe

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Now the storage. This Promise EIDE card is really fast. Has primary port on VLB with speeds up to PIO-3 and extra secondary port on ISA for CD-ROM + serial and parallel port and floppy. To save a slot and reduce the clutter I won't be using its game port and the extra serial port.

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I don't blame anyone using spinning HDDs in their retro builds. But CF cards are way more practical in many ways. The best thing is that with an angle pin connector I can install it directly on the controller without wiring any ugly ribbon cables around

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I had a small dilemma about the primary sound card. I settled on this 1994-made Gravis Ultrasound Max:

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GUS can be a very temperament card. Let's put a Sound Blaster Pro 2.0 as a backup. I hope I will be able to use these two beasts together.

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Last edited by mpe on 2019-10-05, 13:35. Edited 2 times in total.

Dependency Injection Blog||486DX-50 EISA|NexGen Nx586

Reply 4 of 48, by mpe

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As for PSU. I decided to use this 250W Seasonic SFD model. There is no -5V line, but 250W is plenty and it is small and quiet.

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Nothing special about RAM modules. 4x8MB RAM. The mother board supports 192MB. But 32MB is more than enough for DOS. Surprisingly NxVL can happily take EDO chips (although it doesn't seem to be using EDO timings).

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Last edited by mpe on 2019-10-05, 14:14. Edited 2 times in total.

Dependency Injection Blog||486DX-50 EISA|NexGen Nx586

Reply 5 of 48, by mpe

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Intel486dx33 wrote:

How much ram does this motherboard support and what type ?
What about cache ?
What OS’s are you going to use ?

See the later post about the RAM

The cache is soldered on the motherboard. NexGen is using dedicated L2 cache bus and built-in L2 controller which Intel did got until Pentium Pro or so. There is 256kB of L2 cache onboard. 486/Pentiums had to starve with L2 and memory on the same bus.

As for the OS. It will be MS-DOS 6.0 + Windows 3.11.

I am still not sure about Windows 95.

Last edited by mpe on 2019-10-04, 22:42. Edited 1 time in total.

Dependency Injection Blog||486DX-50 EISA|NexGen Nx586

Reply 6 of 48, by mpe

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To mount the baby-AT motherboard into ATX case I had to get one of these 3D printed motherboard shields from the eBay (is the maker on this forum? If so. Thank you!):

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It worked really well. Just had to cut a hole for the DIN keyboard port:

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(to be continued)

Any comments about my part choices? Anyone running SBPro + GUS in the same system (other than the ACE obviously).

Dependency Injection Blog||486DX-50 EISA|NexGen Nx586

Reply 7 of 48, by BinaryDemon

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Oh I like the idea of those IO shields, easy to cut out just the parts you need. I’ll have to give them a try.

Check out DOSBox Distro:

https://sites.google.com/site/dosboxdistro/ [*]

a lightweight Linux distro (tinycore) which boots off a usb flash drive and goes straight to DOSBox.

Make your dos retrogaming experience portable!

Reply 8 of 48, by Vynix

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There was indeed some Nx586es that had a FPU integrated, IIRC they had a "F" in the model name, for example a Nx586-PF90 would be the same as your P90 but with a FPU.

NexGen did indeed make a separate FPU (the Nx587) but no known motherboards supports it, so if you want a Nx586 w/ FPU, you don't have many choices and as such will have to go into a wild goose chase for the Nx586-PFxx CPUs which are rarer than regular Nx586es.

Proud owner of a Shuttle HOT-555A 430VX motherboard and two wonderful retro laptops, namely a Compaq Armada 1700 [nonfunctional] and a HP Omnibook XE3-GC [fully working :p]

Reply 9 of 48, by mpe

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True. However, I believe PF cpus are only compatible with the PCI motherboard AFAIK.

And I don't have one 🙁

Dependency Injection Blog||486DX-50 EISA|NexGen Nx586

Reply 12 of 48, by mpe

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Nexgen is a very unusual socket. Given by its dedicated L2 cache bus it has way more pins than an ordinary Socket 4/5/7 Pentium, leaving alone Socket 3 from 486..

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Another challenge was which heatsink to use. The socket has 4 off-centre mounting points. I don't have the original cooler. Ordinary Socket 5/7 coolers don't fit. Or at least not very well. In the end I decided to use a simple spring based passive heatsink made for Pentium 75-100.

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Hope this passive cooling will be enough.In 1994 active cooling was sill an exception rather than the norm. Furthermore, there is a big case fan blowing air just next to it. And if that proves to be insufficient I can always retrofit a fan to the heatsink.

Dependency Injection Blog||486DX-50 EISA|NexGen Nx586

Reply 13 of 48, by digger

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Cool build!

So what's the FSB speed that this CPU runs on? Isn't 40MHz or so the maximum you can push VESA Local Bus on decent motherboards, without losing stability?

Reply 14 of 48, by mpe

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The CPU runs at 83.3 MHz.

The VL-Bus runs at 1/2 which is 41.6 MHz. I am lucky that both the Hercules VGA and the Promise controller handle that without any extra wait states.

The thing with VLB and high frequency is that the signal is weaker more slots you use.

At 33 there shouldn't be problem driving 3 cards (and some motherboards have three slots). At 40 MHz you can usually run 2 decent cards. At 50 MHz you are lucky to be able to use one.

I've had a 50 MHz 486 VL-Bus system and it was no fun

Dependency Injection Blog||486DX-50 EISA|NexGen Nx586

Reply 15 of 48, by digger

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It's nice to see you push the envelope, though. 😉 Intel played it safe by having their i486DX2 run the bus at just 33 MHz.

Reply 16 of 48, by Anonymous Coward

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What you quoted should be for VLB 2.0.
For VLB 1.0, I'm pretty sure it's 3 cards at 25MHz, 2 cards at 33MHz, 1 card at 40MHz and at 50MHz only one device if it's integrated onto the motherboard.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 17 of 48, by mpe

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One thing I don't like about layout of this motherboard (and many other VL-Bus boards for that matter) is using long ISA cards.

Gravis Ultrasound Max is a vey long card. Almost a full-length ISA. Given that two bottom slots (where I would normally put the GUS in a "normal" system) are taken by VL-Bus cards, I needed to put GUS above. And then it the CPU heatsink gets in place.In fact when in the fifth ISA slot the tall Lettice chip on the GUS is almost touching the CPU heatsink. Furthermore the long GUS is stealing airflow from the CPU. Not good.

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Luckily. The GUS Max 1.8 is not the only one in my collection. I also have revision 2.1 which is noticeably shorter than the 1.8.

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Together with squeezing GUS one port down (where it is now a bit touching the ribbon cables coming out of the IDE/FDD controller) I more or less achieved the separation I wanted:

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Dependency Injection Blog||486DX-50 EISA|NexGen Nx586

Reply 18 of 48, by mpe

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Anonymous Coward wrote:

What you quoted should be for VLB 2.0.
For VLB 1.0, I'm pretty sure it's 3 cards at 25MHz, 2 cards at 33MHz, 1 card at 40MHz and at 50MHz only one device if it's integrated onto the motherboard.

An the VLB 2.0 is the one that never shipped right? In that case I am out of the specs. But somehow it works...

Dependency Injection Blog||486DX-50 EISA|NexGen Nx586

Reply 19 of 48, by Anonymous Coward

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I think some boards might have had VLB 2.0, but I don't think there are any 2.0 cards.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium