If they work, they work. These are passive devices, nothing to worry much about.
For the first one you'll need a cable and a place to mount it in the case.
The second one can go directly on the IDE connector of the motherboard, but you obviously loose the option to add a slave device.

uhm, it's nice to hear this should be as simple as that.
Just in case someone else has a comment, and to save him/her from a potentially lengthy write-up, I will add that I'm aware that with larger disks old OSes and BIOS probably won't see them in full and that there is a universe of software overlays and utilities I might have to dive in.

Those devices work fine and cause no issues, however not all computers (mainly old ones, like 286 or 386) seem to like working with any CF card. I have not had any issues with Pentium machines using those adapters, though. Only annoying thing is that they use the floppy connection instead of the HDD molex for power.

Probably more of an annoyance with more modern PSU and more ancient PSU than circa 1990ish to 2003ish PSU which might have had floppy power on each "vine" of drive connectors, whereas later they only came with a single one, and prior, not at all. But they're a common/standard pin pitch, so it's not hard to splice something to fit, just label it well if it doesn't have the alignment tabs.

I would get one that doesn't require a cable.

Yeah compatibility has a lot more to do with the system and the CF card than it does with the adapter. For example, there are some CF cards for whatever reason that are locked to 'removable device' mode and most vintage systems won't boot from them. Very hard to tell which are like that without just trying for yourself though.

some of those adapters have a jumper to switch between 5v and 3v3 volt, of those that have this option, there're those that use diodes to drop the voltage, which isn't very nice, and those that use an actual LDO regulator.
the latter are hardest to find, though slightly better.

I'm still looking at my options and I realized "133x" in the not-so-expensive cards might mean only 15/20 MB/s , which I assume is low even for DOS gaming...

What would be a usable speed that I should be looking for? 50 MB/s? 60 MB/s?

Also, generally speaking, what size of card could I expect (*) to be recognized by a socket 3/5 board using overlay software?
Just 2 / 4 GBs at best or there is some chance for bigger cards?
(*) I know there will be no guarantees as it varies due to several factors.
(Sorry, for every post I find pointing in one direction I find another one suggesting the opposite...)

Edit: I've found most on my "disk & partitions size" questions answered here:
Re: cf 4gb in dos 6.22

TIA

Low for dos gaming is like 500kb/sec, which is what you'd get on an era and budget* appropriate 80MB PIO mode 1 drive on an ISA controller. Past the mid 90s you might get 2.5MB/sec on your fancy DMA mode 2 1GB drive in 96... then 5,10, 15, 20, until 30MB/sec was reasonable at around 99-00 and then 40 50 60 (introduction of SATA1 🤣 the drives can't soak ATA133 yet) 70, 80...

* what normal gamers could actually afford, not the thousands of dollars 5MB/sec caching SCSI controller with the thousands of dollar 350MB full height hard drive that was "out" in 93 so obviously everyone had one.

AngryByDefault wrote on 2021-06-10, 23:52:

I'm still looking at my options and I realized "133x" in the not-so-expensive cards might mean only 15/20 MB/s , which I assume is low even for DOS gaming...

The question is, does the socket 7 motherboard you intend to use support UDMA? It was not common, UDMA was introduced in 1998. If not, you won't even reach the limit of a 133x card with that controller.

Not sure about DOS but I know the "best" I can get out of my i430VX-based socket 7 system under Linux is MWDMA1 (using a CF->IDE adapter connected directly to the board).

BitWrangler wrote on 2021-06-11, 14:15:

Low for dos gaming is like 500kb/sec, which is what you'd get on an era and budget* appropriate 80MB PIO mode 1 drive on an ISA controller. Past the mid 90s you might get 2.5MB/sec on your fancy DMA mode 2 1GB drive in 96... .

Great references. I guess making a first attempt with a modest card will be worth the "risk".

konc wrote on 2021-06-11, 14:44:

The question is, does the socket 7 motherboard you intend to use support UDMA? It was not common, UDMA was introduced in 1998. If not, you won't even reach the limit of a 133x card with that controller.

Both boards (still undelivered actually) seem to support UDMA (UDMA33 one, UDMA66 the other), but it is obvious now (to me) that if I ever get a Socket 3 it won't have UDMA.

Based on this I've decided to try to get one of the "known-to-work" adapters and get a second hand card as a first attempt. BUT I'll get the adapter from overseas through a new "ebay-ish" site at a third of the local cost;

so I'll be also testing that sourcing with a small purchase, great deal if it works, not so painful if it doesn't....

By the time I get an Sk3 (if ever) I will have some hw to try before forking the cost of a modern SSD for a meager 4 GB card that might not even work for me.

Thanks again!

AngryByDefault wrote on 2021-06-11, 17:46:

Both boards (still undelivered actually) seem to support UDMA (UDMA33 one, UDMA66 the other), but it is obvious now (to me) that if I ever get a Socket 3 it won't have UDMA.

Socket 3 will probably tops at PIO 4 mode, so i'll be OK with that CF.

konc wrote on 2021-06-10, 14:26:

If they work, they work. These are passive devices, nothing to worry much about.

I think the same. The only thing I noticed with a few of the simpler adapters is, that they do not have the traces for DMA.
Anyway, that's no issue in MS-DOS (and Win 3.x), normally, since it is entirely PIO driven.
The only exception of DMA use I can think of is FreeDOS with one of its optional UDMA drivers.

Ok, so FWIW I got the one from the first picture but with a molex connector.

So far so good, it seems to work reliably and it even has a master/slave jumper. Doesn't have any activity lights, as some fancier ones, but it is doing its job at a third of the cost.

I still haven't run any thorough test yet but had zero issues so far. I tried both 40 and 80 wires cables and two very different mainboards.

I hope to eventually run some benchmarks and post'em if there's any point to it.

Regards.

Glad to hear that it works! ^^

If you like, you can these for benchmarking, for example:
- CheckIt! v3 or v4
- SpeedSys
- Syschk
- Sysinfo by Central Point Software or Symantec

NSSI and Dr.Hardware Sysinfo may also support benchmarking, not sure if it works for HDDs, though.