Can you try FTP download to NUL, in BINARY mode?
What's the CPU?
Do you have a managed switch? What's the link speed and duplex mode?

Edit:

You're using the latest drivers, right?

83-0809-001
3Com Fast EtherLink ISA Parallel Tasking 10/100 Base-TX
Version 2.0
Copyright 1997 3Com Corporation. All rights reserved.

Thanks at first for your response.

Reg 1: download to NUL to my understanding requires Linux. Is this right? How to do this in dos/win95 env? AFAIK NUL in dos is a hidden system reserved directory

Reg 2: See my specs for system 1 in my signature. ISA at 16MHz. Should hopefully not be important for real busmaster ops

Reg 3: yes managed switch with OpenWRT. Pls let me check the handled-out speed pls. Good remark. Max speed supported by the 515 config tool is 100MB HD

Reg 4: pls let me check as well. I use the driver out of vogons driver library (515n and 515x.exe). I am not aware of any other versions available even after searching through the whole internet 😀 I know it’s indeed a 1997er version.

Marco wrote on 2025-10-24, 20:16:

Reg 1: download to NUL to my understanding requires Linux. Is this right? How to do this in dos/win95 env? AFAIK NUL in dos is a hidden system reserved directory

Download to /dev/null requires Linux, or any other Unix-style system.
Download to NUL requires DOS, Windows, or OS/2.
For example:

ftp 192.168.100.200
bin
get SomeBigFile.zip nul

Reg 4: pls let me check as well. I use the driver out of vogons driver library (515n and 515x.exe). I am not aware of any other versions available even after searching through the whole internet 😀 I know it’s indeed a 1997er version.

I can only see this - https://vogonsdrivers.com/getfile.php?fileid= … &menustate=47,0 - which is the older version:

83-0809-000
3Com Fast EtherLink ISA Parallel Tasking 10/100 Base-TX
Version 1.0
Copyright 1996 3Com Corporation. All rights reserved.

I'm attaching the newer thing...

Fantastic. Let me check this over the weekend to come back here afterward. Much appreciated.

Some more ideas...

That TI "486" CPU may be pretty fast internally, but the external bus is still 16-bit = slow I/O.
Don't expect 100 Mbps to be much faster than 10 Mbps - but it shouldn't be slower, either.
Have a look at this post - Re: Expected network throughput on ISA network cards

Especially, note the "tune the DMA parameters" procedure - it may be important!

Did you try to Pump up ISA Bus Speed ? maybe to 10 or 12Mhz ?

matze79 wrote on 2025-10-25, 09:27:

Did you try to Pump up ISA Bus Speed ? maybe to 10 or 12Mhz ?

Looks like he did:

Marco wrote on 2025-10-24, 20:16:

ISA at 16MHz.

Maybe that's the problem. Remember that ISA is asynchronous and sometimes decreasing the cycle time just makes the card add more cycle waits

Could indeed be. Thanks. I will investigate

Very good link indeed. Thanks. I forgot to mention that I also tested things on a 486 DX2 80 with similar results though

Some more facts, potentially relevant:
- the 1996 driver for Windows 95 is VXD (LE)
- the 1997 driver is SYS (PE), for Windows 95 and NT 3.51/4.0

I have no idea about the possible impact on performance, but it may be worth investigating...

So. I used the weekend to test some details on the driver side:

- vogons: vxd drivers from 96
- 3c515N.exe: sys drivers from 04/97
- 3c515X.exe: sys drivers from 09/97
—- oemsetup.inf identical. File size of drivers differs. Version of driver file is both time 1.06.
- win98: does seem to use the same drivers from 4/97. same filesize etc

So far no performance differences noticed.

While testing the NDIS2 drivers under MSclient I noticed following sentence during loading: „Bus mastering disabled by EEProm on Adapter.“

First: interesting information.
Second: any idea what could be the reason for this? In the 3c515cfg you cannot configure anything like that. All tests do pass fine.

Any ideas here?

I hope it’s not the case that my board doesn’t support bus master Dma. But it would be new to me that this is mainboard dependent. According to the manual busmaster requests / commands are being accepted and handled. Or it requires a PnP board or sth. Anyway, dont want to put anyone here on a wrong track with these thoughts.

Thank you

Update: just found this release note:

IBM 486 SLC and IBM 386 SLC PCsThe 3C515-TX NIC does not run in bus master mode onthese PCs. To disable bus mastering on your PC, referto readme.txt

My cpu is similar although not exactly the same. I would assume things could be related to this fact. I will therefore test the BARB settings for this cpu as recommended by user feipoa.

The IBM SLC CPUs were very odd beasts, and different in some ways to other (Ti/Cyrix) SLC designs out there - but this could be a common factor. However even if it's not, this is a very slow system to be pushing relatively high networking speeds. I'd be curious what results you'd get with a faster system, in particular one where other I/O doesn't go over the ISA bus (i.e. a VLB or PCI 486 system) - your system 2 for example 😉

Thanks. If I willigend time will do this benchmark (but as written I think I already did it - will look for details). Furthermore the performance did not increase while going from 386sx25 to ti486sxlc2 60. thus it doesn’t seems to be cpu bottleneck issue

Marco wrote on Yesterday, 21:53:

- 3c515N.exe: sys drivers from 04/97
- 3c515X.exe: sys drivers from 09/97
—- oemsetup.inf identical. File size of drivers differs. Version of driver file is both time 1.06.

Looks like the difference is that the later file has symbol table stipped.

Anyway - I don't know what exactly is necessary for the ISA bus mastering to work.
And I don't have any of those "486 inside, 386SX outside" oddballs.

But I have a 486DX2-66 with ISA+VLB, where I can do some benchmarks.
If your problem is also visible on your 486DX2, perhaps it will be helpful if we compare our results...

Will do detailed benchmarks asap.

1st update: changing barb/flush methods for the cpu cache couldn’t solve the message

2nd update: still trying to find a usable FTP server for downloading to NUL. Ideas welcome

If you'd like to test card raw Ethernet transfer without the overhead of TCP/FTP,
SMB or other higher-level network protocols.

Check out my DDLINK it runs under DOS and needs only a "packet driver" to
communicate with your network card. DDLINK communicates with another node
using it's own very simple protocol within the lowest level network packets (to give
you an idea of how simple the DDLINK protocol is - it can also transfer file over a
serial or parallel connection)

Although DDLINK is mainly an interactive file transfer tool, it does have an
option to automate keyboard input keys - so you can make it effectively a single
non-interactive command to transfer a file (which can be easily timed)

Thanks for the hint. There are unfortunately no packet drivers available for the 515 😒

Marco wrote on Today, 14:15:

2nd update: still trying to find a usable FTP server for downloading to NUL. Ideas welcome

I use ProFTPD under modern Linux.
Though any should work - serving files via FTP isn't rocket science...

Marco wrote on Today, 18:08:

There are unfortunately no packet drivers available for the 515 😒

Well, there's this project - https://github.com/jfabienke/3com-packet-driver - but no releases yet...