8087-1 FPU has been added.
No real difference in SimCity observed. Will check later with some other tools.

H3nrik V! wrote on 2026-06-18, 14:09:

JAKra85 wrote on 2026-06-18, 12:07:

- Turned on, measured voltages. All good. I got 10,8V instead of 12V and also got a bit sad at this point and less confident about this PSU... too late.
- Tested on a different low value AT board. Measured again, exactly 12.00V (and 4,99V).
- Important: with no load the 12V measures way less that 12V!

I would fear that the lower unloaded voltage could be a symptom of some regulator not working correctly - maybe from dried up capacitors?

I might have used a wrong phrase or wording here.
Unloaded not equal to powered on and idle state.

In this case I used "unloaded" as not connected to anything. With PSU powered on and AT pins P8 and P9 hanging in the air and measured voltage.
Upon further investigation this is natural as many classic power supplies require a load on the 5V or 12V rail to properly regulate and output correct voltages.

"- Tested on a different low value AT board. Measured again, exactly 12.00V (and 4,99V)."
Measured this by connecting to an AT motherboard, powered on and low load.

JAKra85 wrote on 2026-06-18, 14:50:

8087-1 FPU has been added.
No real difference in SimCity observed. Will check later with some other tools.

SImCity uses the FPU in specific circumstances, you wouldn't really see a benefit in moving around a map

https://michaeldale.com.au/archive/2026/06/07 … y-use-your-fpu/

(The usage is the same for original and 2000)

NeoG_ wrote on 2026-06-19, 04:53:

SImCity uses the FPU in specific circumstances, you wouldn't really see a benefit in moving around a map […]
Show full quote

JAKra85 wrote on 2026-06-18, 14:50:

8087-1 FPU has been added.
No real difference in SimCity observed. Will check later with some other tools.

SImCity uses the FPU in specific circumstances, you wouldn't really see a benefit in moving around a map

https://michaeldale.com.au/archive/2026/06/07 … y-use-your-fpu/

(The usage is the same for original and 2000)

Good read!
I can confirm, not many games used FPU before Quake engine and even those that used it have no breathtaking uplift.

Google AI was misleading with up-to 50% increase... when asking for 8087 FPU upgrade. 😀
Pointed to a Reddit post with SimCity Classic with FPU +50% uplift, that Reddit post pointed to this Vogos entry:
Interesting findings with simcity classic
Yeah, but here it's a 386 with 387 FPU, not really comparable with 8088 with 8087 FPU.

I will do a bit more test and research.

I've read previously that the FPU can become hot, but damn... it's like dangerously hot. Thinking adding some heat sink...
I specifically choose 8087-1 with 10MHz, thinking that if the FPU is rated to 10MHz when running at 4,77MHz it will be cooler than the one rated to 5MHz.

Software written using QB 4.5 does use a math co-processor, if available.

Examples:
https://www.youtube.com/watch?v=mYJ1IPph4tw
https://www.youtube.com/watch?v=FaQa9INqZf8

Edit: This might be of relevance in so far, because QBasic/QB had quite a community in 90s and early 2000s.
Many applications and games had been written using them, many websites had offered QB 4.5 examples and tutorials.
So depending on the situation, the QB runtime can make use of the x87 math co-pro.

Very cool system! 😀

Irinikus wrote on 2026-06-19, 15:20:

Very cool system! 😀

Thanks!
I keep improving it. 😀

Jo22 wrote on 2026-06-19, 07:42:

Software written using QB 4.5 does use a math co-processor, if available. […]
Show full quote

Software written using QB 4.5 does use a math co-processor, if available.

Examples:
https://www.youtube.com/watch?v=mYJ1IPph4tw
https://www.youtube.com/watch?v=FaQa9INqZf8

Edit: This might be of relevance in so far, because QBasic/QB had quite a community in 90s and early 2000s.
Many applications and games had been written using them, many websites had offered QB 4.5 examples and tutorials.
So depending on the situation, the QB runtime can make use of the x87 math co-pro.

Thank you! I've done some benchmarking and now I am sure the FPU is there and working. That is enough for me.
The past few days I was thinking on the purpose of this system.
Now I have 2 (maybe 3) goals:

1) SimCity Classic "ultimate gaming machine" with mouse and playing on the original 5151 monitor. Running the game in EGA is barely playable, it does not matter if EGA mono or EGA color. Resolution matters.
2) Very simple e-mail sending station. I think it's cool to be able to send even a simple e-mail from the original PC to any modern device.
3) Copy files to and from; over the network. I had enough of floppies.

Any other ideas?
Don't forget I only have 10MB total and about 2MB free.

Double trouble!

I have a back-up drive to this machine in case the primary dies (when it dies).
The one used right now is made in Singapore, the back-up drive is made in USA.
Tested it... and it was not working. Applied the same trick that is mentioned in the first post and now it works fine.
Drive had been formatted and copied the system files.
Booting. Put it aside in a safe place, not the attic (it gets too hot in the summer).

More pics:

JAKra85 wrote on 2026-06-18, 14:50:

8087-1 FPU has been added.
No real difference in SimCity observed. Will check later with some other tools.

I don’t know of any vintage dos games that were dramatically accelerated by an FPU but an IBM PC/XT did have floating point and parallel processing upgrade options that were far faster than 4.77mhz.

Similar to the later 287 upgrades there were ways of running your 8087 at speeds higher than 4.77mhz on your XT.

There were also 10-16mhz accelerators that included 287 or 387 chips or even non-x86 parallel processors like the 68k that could be supported by database and lotus 123 with a driver.

In the case of sim city have a slow 8088 combined with a light speed floating point may still not do much.

JAKra85 wrote on 2026-06-16, 19:59:

Thank you for the detailed description! I set the IBM 5151 monitor aside, takes too much space. Now only using the VGA with thi […]
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Jo22 wrote on 2026-06-05, 23:12:

Hi, it might be that PC-Tools Deluxe from the 80s checks for full 256 KB or less. 256 KB was the full expansion for EGA cards an […]
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JAKra85 wrote on 2026-05-24, 21:33:

Today I brought it down, did a clean, disassembled made photos, reassembled. Changed the videocard to ATi Wonder 1024 - ISA - 51 […]
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Today I brought it down, did a clean, disassembled made photos, reassembled.
Changed the videocard to ATi Wonder 1024 - ISA - 512KB (PN 109-00095-10).
One of the fastest videocards possible from ATi (28800-5) for this CPU.
This is a 16b ISA working in 8b ISA mode.
The PC Tools program reports only 256KB RAM on the videocard, not exactly sure why that is.
Has both VGA and EGA outputs.
(Tried IBM 5151 monitor and an LCD at the same time, does not work. 😜 )

Hi, it might be that PC-Tools Deluxe from the 80s checks for full 256 KB or less.
256 KB was the full expansion for EGA cards and the base memory for VGA cards.
So the register in memory can't tell if its 512 KB or 1 MB.
Other programs might report "256 KB/512KB" instead.
Merely VGA aware programs do really count the video memory, I think.

https://dosdays.co.uk/topics/Manufacturers/at … vga_wonder+.php

I was just curious to see what happens if VGA and MDA are connected at the same time. There was no motive behind it, only curiosity.
The MDA monitor did not get a signal.
With this videocard it takes a bit of time for the MDA monitor to get a signal. Maybe I will try by attaching the VGA after I have an MDA output.

This works just fine, if two cards for each monitor is used.
VGA and MDA can co-exist, an MDA monitor was often used by developers to see debugger output (SoftICE, Windows etc).
Things is, there are two types of MDA cards.
Real MDA cards with 4 KB of RAM and MGA (Hercules, HGC) cards with 64 KB of RAM.

But because Hercules cards do boot up as plain MDA cards, as well, they cause no trouble.
Programs like Checkit will merely see a plain MDA card in short.
It needs a driver or utility to enable the graphics RAM (Hercules driver disk, msherc driver etc).

If other graphics cards can be used in graphics mode or not is up to the VGA BIOS.
It has to be smart enough to decide if the VGA card makes room for another graphics card.
If it makes room, the VGA card looses some of its video modes.

Edit: Two monitors on one VGA card may or may not work.
I vaguely remember that some VGA cards from late 80s (ATI?) had "auto-sense" and would try to detect the monitor type.

Thank you for the detailed description!
I set the IBM 5151 monitor aside, takes too much space.
Now only using the VGA with this IBM XT.

I now have other issues, I think it could be videocard related.
I need assistance/advice if and how I can fix this.

1) There is a corruption visible in SimCity. It's a mouse trailer issue, I do not know how to better describe it. 😀
Since I do not yet have a mouse I'm using the keyboard to move the cursor.

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2) After 10-15 minutes there is a fuzziness on the screen, it might be PSU related.
When the PC boots everything is clean and clear after a time I see this fuzziness and it gets worse with time.
It is very strong when both HDD and FDD are active (high load). With less load or idle this does not go away.
Also almost all ISA ports are populated.
I'm thinking of changing the capacitors in the PSU for a cleaner voltage. Manufacture date is 1983 week 41. I don't think anyone touched this since. 😀

The attachment 20260616_211457.jpg is no longer available

"1) There is a corruption visible in SimCity. It's a mouse trailer issue, I do not know how to better describe it. 😀
Since I do not yet have a mouse I'm using the keyboard to move the cursor."

This issue or screen coruption was caused by the ATI Wonder 1024 BIOS (I think) and the keyboard-mouse emulation in SimCity.
Once I've set up an IRQ based mouse the visible corrution was gone.

Next week I think I can complete this project and will post pictures.

IBM XT 5160 connected to the internet!

I have finally managed to connect this PC to the internet.
Originally I have used a WD8003W network card.
I had issues, this 8bit ISA network card: can't do auto-negotiation and can't do full-duplex.
Because of this even if the driver was properly set up and working once connected to my home router (FTTH - 4 Gigabit ports) I had no connection.
I had two options:
1) Man in the middle: An older switch or router between the two parties.
2) Change the network card with something more recent that still works in an 8bit ISA slot and the IBM XT (4,77MHz) CPU.

I took option two:
3Com EtherLink III (3C509B-TPC)
Made in 1997; Made in USA. 😀

I use it currently to set the system time. There is no RTC on an IBM XT.
Later I plan sending simple e-mails from it.
Once (or if) I open a Retro PC Gallery to the public, users will be able to send an e-mail from the original IBM XT to any modern device.

Current autoexec.bat:

Current mTCP config file:

IBM XT booted and time set:

Next is the sound card.
I already have it, it is set up and working.
The problem I have is that the bracket is missing...

I already tried two (non-Creative) brackets and they did not fit, it's not a standard.

Once this sound issue is solved it's project complete.
Photo time and putting it aside for later.

rmay635703 wrote on 2026-06-25, 19:49:

I don’t know of any vintage dos games that were dramatically accelerated by an FPU but an IBM PC/XT did have floating point and […]
Show full quote

JAKra85 wrote on 2026-06-18, 14:50:

8087-1 FPU has been added.
No real difference in SimCity observed. Will check later with some other tools.

I don’t know of any vintage dos games that were dramatically accelerated by an FPU but an IBM PC/XT did have floating point and parallel processing upgrade options that were far faster than 4.77mhz.

Similar to the later 287 upgrades there were ways of running your 8087 at speeds higher than 4.77mhz on your XT.

There were also 10-16mhz accelerators that included 287 or 387 chips or even non-x86 parallel processors like the 68k that could be supported by database and lotus 123 with a driver.

In the case of sim city have a slow 8088 combined with a light speed floating point may still not do much.

Original SimCity with a 8088 CPU and 8087 FPU is quite playable on an MDA monitor\resolution.
I don't plan any accelerators, this is good enough to enjoy.
If I want more speed, I have over 30 PCs that are faster than this one. 😁
I was simply curious of the speed change once an FPU is added. - Barely noticeable.

JAKra85 wrote on 2026-07-13, 18:02:

Current autoexec.bat:
[...]
IBM XT booted and time set:

Your TZ variable is only good for the summer time.
For the whole year, use:

set TZ=CET-1CEST-2,M3.5.0/02:00:00,M10.5.0/03:00:00

Grzyb wrote on 2026-07-15, 12:18:

Your TZ variable is only good for the summer time. For the whole year, use: […]
Show full quote

JAKra85 wrote on 2026-07-13, 18:02:

Current autoexec.bat:
[...]
IBM XT booted and time set:

Your TZ variable is only good for the summer time.
For the whole year, use:

set TZ=CET-1CEST-2,M3.5.0/02:00:00,M10.5.0/03:00:00

Big thanks! 😀
Set, checked and working nicely! (<- Will check again during winter.)

Changed the two RAM cards (2x256KB) to one 768KB RAM extension card with RTC mentioned in one of the previous entries.
(this system by default can use a max. of 640KB and that is fine, I don't mind the "lost" RAM)

Also sent it to TheRetroWeb: https://theretroweb.com/expansioncards/s/atd-model-116

Unfortunately the RTC chip (ATD-20) is dead and it is not a DS1287 or DS12887.
I did not want to brake it apart, left it like it is.
Previously I've already modified a DS12887 to "look good" and work at the same time:

The system time is synced over the internet (SNTP) during the boot sequence so nothing is lost.

There are utilities to “use some of the lost ram”

Use!UMBS comes to mind.

As long as it's in the 384k adapter rom area, that can turn it on as upper memory, even on an XT.

Project complete!
IBM XT 5160 connected to the internet with time&date synced&set:

Pinging google.com:

ISA cards nicely lined up:
Microsoft InPort - MS Bus mouse card
3Com EtherLink III - LAN card
Western Digital WD1002A-WX1 - MFM hard disk controller
A.T.D. Model 116 - Memory expansion card
ATi Wonder 1024 - Video card
Creative Sound Blaster 2.0 - Sound card with CMS Upgrade
FDC - Original IBM floppy drive controller

Back:

Copying game Tetris from a Windows 11 PC to the IBM XT trough FTP:

Playing SimCity:

AMD CPU and Intel FPU playing nicely with each other. 😀

Now, I just need time to enjoy it. 😀