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Cx486drx2

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nc_mike

Experienced Member
Joined
Sep 28, 2014
Messages
473
Hi,

I am looking for a CX486DRX2-16/33GP or CX486DRX2-20/40GP clock-doubled 386DX >> 486DX CPU upgrade. I'd like to use it to replace the 16Mhz 80386D CPU I have in my Intel InBoard/386 PC. I understand I might can use some other 486DX chips, but this one is specifically clock-doubled (its drivers also requires the drivers to do so). I've bee told I can use either the 16/33 or the 20/40, but when using the 20/40 the CPU will still max out at 33MHz - but both a pin and board compatible with the InBoard.

Now I've been searching the net and waiting for one to pop up eventually on eBay, but I did notice a seller called Quest Components that lists having a stock of 182 of the CX486DRX2-20/40GP CPUs @ $26 each. Does anyone know if this is a reputable source? ( http://www.questcomp.com/QuestDetails.aspx?pn=CX486DRX2-20/40GP&pnid=349584&stock=YesOnly )

Regards,
Mike

-------------------------------------------------------------
Reference sites with information about the Cyrix CX486DRX2 CPUs

http://ps-2.kev009.com/ohlandl/8570_Tim_OConnor/cyrx.htm

http://www.atarimagazines.com/compute/issue158/128_Cyrix_Cx486DRx2.php
 
I have a similar processor from Texas Instruments, also an insocket 386 to 486 replacment, have to look for the exact name, but I think it does not double the clock. I am probably interested to get also two of these Cyrix for two 386 systems I have. The TI needs a driver at startup to enable it's enhanced features, does the Cyrix, too? I am also sesrching for the TI driver.

Edit: I think it's the first one here: http://www.cpu-collection.de/?l0=co&l1=Texas Instruments&l2=486
 
Tx486dlc/e-40ga

Tx486dlc/e-40ga

1ST1 said:
I have a similar processor from Texas Instruments, also an insocket 386 to 486 replacment, have to look for the exact name, but I think it does not double the clock. I am probably interested to get also two of these Cyrix for two 386 systems I have. The TI needs a driver at startup to enable it's enhanced features, does the Cyrix, too? I am also sesrching for the TI driver.

Edit: I think it's the first one here: http://www.cpu-collection.de/?l0=co&l1=Texas Instruments&l2=486
Click to expand...

Yah, I think you might be referring to the TX486DLC/E-40GA. What I've been told is without the clock doubling its not going to buy much. Yes, the Cyrix has drivers to enable its features at boot up as well.

Regards,
Mike
 
You can easily replace the oscillator on the Inboard with a faster one.
I used a 50mhz (=25mhz cpu clock) oscillator, but that was a bit unstable.
A 40mhz quartz will work on almost every Inboard386.

The TI 486DLC are really cyrix 486 cpus. The cyrix driver/config software will work with them as well.

If you want to have the maximum of speed boost, you should get a TI 486 SXL(2) with -40 or greater rating.
The -40 Chip has the capability to be clock doubled but it does not have this feature enabled.
The SXL2 Chip has the clock double feature enabled out of the box.

All cyrix Chips have 1k of L2-cache.
Only the SXL TI-Chips have 8k of cache, 16bit 486 (SLC) not taken into account.

The IBM 486/386 chips wave up to 16k, but are really hard to come by and never appeared (to my knowledge) in 386DX PGA format.
 
You could use the DRx2-25/50 and 33/66 as well if you could find those.

Neither the ti486SXL or SXL2 have clock doubling enabled by default. They both require a utility to enable it. The DRx chips make better drop in upgrades for older systems since they have a built in cache coherency circuit. The stock Cyrix and TI DLC/SLC/SXL chips normally require an adapter or a modification to work properly with the cache enabled.
 
Anonymous Coward said:
You could use the DRx2-25/50 and 33/66 as well if you could find those.

Neither the ti486SXL or SXL2 have clock doubling enabled by default. They both require a utility to enable it. The DRx chips make better drop in upgrades for older systems since they have a built in cache coherency circuit. The stock Cyrix and TI DLC/SLC/SXL chips normally require an adapter or a modification to work properly with the cache enabled.
Click to expand...

After mulling it over a bit, I don't think I am up to the task of replacing the oscillator on the InBoard - I'd probably screw it up and blow the entire board (I'm more of a software guy and not very good with a solder gun). I have to admit the 8K cache vs the Cyrix 1K cache would be sweet, but then again I fear my clumsy self screwing up the board.

I did get email confirmation from Quest Components that they have 182 of the CX486DRX2-20/40GP CPUs in stock @ $26 each, so that seems very reasonable. I found the software at http://ps-2.kev009.com/ohlandl/8570_Tim_OConnor/cyrx.htm (who says its 3.30 version supports Dos/WfW/OS2/NT3.5).

One of the issues I'd need to contend with is the expansion slots. The CX486DRX2-20/40GP actually has a heat sink which I can also get pretty easily from eBay (it looks like any of the Cyrix dX2 486 heat sinks will suffice). The 16/33 version if of the CX486DRX2 apparently doesn't come with or require a heat sink, but I've not been able to locate one of those 16/33 CPUs. My question is, since the 20/40 will still only run at 33MHz (I was informed), can I go without using a heat sink with it? I ask because if I have to use the heat sink I am going to have to lose a slot and one adapter (probably lose my sound card and move the Ethernet card over to Slot 3) to make enough clearance for the heat sink in my 5160. According to Intel, the Inboard has to go into Slot 5 or Slot 6 (mine is presently in Slot 6). In Slot 7 is a half length Ethernet adapter which doesn't provide enough room for a heat sink next to it. In slot 8 is my XT-IDE which sits low enough to likely not interfere with the heat sink. I'd have to clear our Slot. Of course if I could find a 5161 expansion chassis.... :)

Here is the current layout of my expansion slots:

Expansion Slot Usage
____________________

Slot 1: Intel AboveBoard Plus 8 with 8MB of EMS
Slot 2: Ati Graphics Ultra Mach8 video adapter with 1.5MB RAM
Slot 3: Sound Blaster CT1350B
Slot 4: Digitial Research Super ISA multi-function adapter
Slot 5: VTG FA-100 1.44M/1.2M FDC
Slot 6: Intel Inboard/386 PC 80386DX 16MHz 1MB with 4MB daughter card
Slot 7: 3Com Ethernet III 3C509B RJ45 Ethernet Adapter
Slot 8: XT-IDE adapter

Regards,
Mike
 
Last edited:
Anonymous Coward said:
a 20/40, 25/50 and 33/66 should all have the same thermal properties as the 16/32 as long as you keep the bus at 16MHz.
Click to expand...

Awesome....I didn't want to fry the CPU and socket if I go w.o the heat sink.

So I am told I can use a 16/33 or a 20/40. I got the sense I can't use a 25/50 or 33/66, but don't know if that is true or not. Also, I assume the 5160 use limitations of the InBoard's XMS remains even with one of these processors (I assume its a BIOS thing)? Weird, I read a clause in the Inboard guide that said I could use the XMS with a vdisk to access XMS for apps, but I don't see how that wouldn't just act as just another vidisk the same as I could make using the AboveBoard EMS. I assume the apps, even if copied to the XMS resident vdisk, still load within the lower 640K for execution, right? It was just the wording that seems to imply otherwise, but I doubt the writer of the Inboard doc meant that.

My system is so packed I end up with about 500K free with everything enabled even after using QRAM to pack all but 3K of upper memory - wishful thinking I could load more above 1K than I can :-0

Regards,
Mike
 
I took the plunge today and now have a quasi XT-486DX-33. The CX486DRX2 20/40MHz arrived in brand new, pristine condition in perfect packaging (almost looks like original inner packaging) and perfectly straight pins. I didn't expect that I get a new unused CPU for $26.

2015-03-02 17.24.25.jpg

I pulled the Inboard/386 adapter out of the case, carefully pulled the 386DX-16 with my chip puller, and dropped in the Cyrix CX486DRX2. Honestly, I was a bit nervous because these InBoards can be damaged easily and are very difficult (near impossible) and expensive to replace.

At first, after doing nothing but installing the CPU and powering up, it showed only a marginal increase in performance without having installed the Cyrix cache software for DOS that enables the cache. I was simply breathing a sign of relief just to see the machine post without error.

I installed the Cyrix cache utility which sped things up nicely. I then went into the CPU registers using the Cyrix config utility and enabled pipelining which boosted the CPU performance quite a bit more. Finally, I installed the Cyrix Windows drivers/utilities and enabled the FASTIO utility and I'm seeing a decent upgrade from a 386 InBoard to a 486. Its certainly not as fast as it would have been with a 486DLC 8K cache and new oscillator, but its not half bad either for an easy upgrade.

I sure wish I had a copy of the Cyrix manual though - there are a whole bunch of register and configuration settings I'd like to know how to adjust to get the most out of the CPU. Anyone know where I can find a copy?

SysInfo7 performance monitor scores it 37.7 vs an 80386-33 @ 35.9, but obviously the smaller cache of the Cyrix will hit actual performance.

2015-03-02 20.28.41.jpg

Interesting that it report the CPU correctly but at 32MHz, not 33Mhz (I didn't expect it to go to the chips 40MHz max, just double the 16MHz)

2015-03-02 20.27.18.jpg

After installing the Windows utilities I got this:

2015-03-02 22.17.18.jpg

And TopBench scored it at a 30 saying it was equivalent to a PS/2 Model 80 (I know my Mod 80 ran Windows faster through...must have been the cache).

Anyhow, its certainly a boost over the 386DX-16 and was easy and worth doing, though I somehow feel there might be a bit more to optimize to get the most out of it if I had the documentation to tweak the CPU settings and registers :)

Regards,
Mike
 
Still seeing the user manual for the Cx486drx2 of anyone (AC, anyone else?) has a copy or a link they can send me.

Thanks,
Mike
 
nc_mike said:
Still seeing the user manual for the Cx486drx2 of anyone (AC, anyone else?) has a copy or a link they can send me.

Thanks,
Mike
Click to expand...

I'd love a copy of the manual as well!

(and thanks for the questcomp link, nc_mike, I'm ordering a cpu)

Edit: 486 arrived, shipping was speedy and everything was packed well.
 
Last edited:
nc_mike said:
After mulling it over a bit, I don't think I am up to the task of replacing the oscillator on the InBoard - I'd probably screw it up and blow the entire board (I'm more of a software guy and not very good with a solder gun). I have to admit the 8K cache vs the Cyrix 1K cache would be sweet, but then again I fear my clumsy self screwing up the board.

I did get email confirmation from Quest Components that they have 182 of the CX486DRX2-20/40GP CPUs in stock @ $26 each, so that seems very reasonable. I found the software at http://ps-2.kev009.com/ohlandl/8570_Tim_OConnor/cyrx.htm (who says its 3.30 version supports Dos/WfW/OS2/NT3.5).

...

Regards,
Mike
Click to expand...

Thanks for the info on Quest Components and the link to the software. I quickly received my CX486DRx2 for my Compaq 386/20e and had it running under DOS, Windows, NT and Linux.

Dave...
 
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