Hi. I've recommended both DOMs and CF cards so far. DOC-2000/DiskOnChip chips, too.

DOMs are ideal, because they're usually SLC and meant exactly for this purpose.
They look like a hard disk, have removable media bit as "fixed" by default.
But they're very small capacity wise.

DOCs can be installed on network cards (?) or custom built ISA cards. They're ancient SSD tech.
They have firmware, also, to map their filesystem into the host system.
That firmware takes up memory in the UMA, like an Option-ROM. XT and AT firmwares exist, a re-flashing might be necessarily.
Also, these chips are slow. int13h interface only.

CFs have a long history and a native parallel IDE interface.
The are available in the 512MB to 8GB range which is nice for DOS systems.
504 MB is the maximum via CHS, ~7GB or ~8GB via E-CHS.

About 8GB is the maximum that Windows 3.1x fast-disk drivers do physically use (no partition thing).
Any larger, and address-wraparounds issues etc may appear.

I'm no fan of SDHC/SDXC cards.
a) because I personally consider them as cheap consumer/mainstream stuff
b) because of the low-quality converters which I had bad experience with (got hot, had shorts etc).

HDDs are nice, provided that they still function. By 2024, though, it's hard to recommend a 30 to 40 years old mechanical piece.
It's like with an electrolyte capacitor or fan in an old power supply.
It may be fine, yes, but actual condition can't be known in before. 🤷‍♂️

Btw, old MFM/RLL may have a bigger chance to be repaired than more modern drives that came after them.
The external stepper motors can be retrofitted with new grease etc.
There's not much electronics on the hard disk itself, after all. It's more a mechanical piece with some electric amplifiers.

Edit: I forgot. MFM/RLL drives usually didn't have auto-parking feature. An MFM/RLL (ST-506 etc) must be parked via DOS utility.

Ideally every time then the PCs gets switched off, but mandatorily if a PCs gets physically moved. Otherwise a head-crash is likely to be happen.

Unfortunately, most users don't know that. Not these days. So any power on test by an eBay seller may impose a danger that the drive won't arrive unharmed.

Edit: SSDs in general have the advantage over HDDs that they have a very fast response time (access time).
That means that a missing hard disk cache on the software side, such as Smart Drive, isn't that of a loss. Memory can be saved by not using it.

However, cheap flash media (SD..) may not be made with random read/write access in mind.
They were designed for digital cameras, camcorders and mp3 players. Which use linear access or sequential access. Either one big file (video recording), or many little ones - but one after another (playing mp3s).

That's why they stutter under Windows 9x. Windows 9x causes a lot of hard disk activity, even during idling.

I remember that from the 90s, when my dad ha 386 running Win95 RTM. The HDD lights were always blinking..

Windows 3.x, DOS or Amiga/Arari ST are different here. They're read-only, more or less. They don't have any background activity.

I've seen a lot more of the SD to IDE boards recently. SD cards are a lot easier to find today, but I don't like the converter boards. They're a little slow and need special formatting on top of being low quality.

I still have real hard drives for the sound, but I know that I will have to switch over to modern storage as they fail (they all have bad sectors, and one feels abnormally slow).

I got into an argument with someone at school in 1991 because I said that I wouldn't use anything but DOS on my machines. I said Windows was fine for some productivity, text editing, etc...but that it was mostly bloat that I didn't need. This guy said OS/2 was superior to everything and would be the primary OS fopr home use going forward. Sounds just like all the linux people for the last 20+ years.

I do think though the longer Linux sticks around and the more evil Microsoft and Apple become that its possible it does eventually take over for home PCs.

TheMobRules wrote on 2024-01-25, 05:50:

I find that for tinkering purposes an old hard drive is no different from an old motherboard, CPU or set of RAM modules.

The one difference I can see here is repairability and replaceability. Motherboards are generally more repairable depending on point of failure. RAM modules have modern replacements being made.

Whereas hard drives can be more difficult to repair or possibly be non-repairable in the event of mechanical failure.

Shagittarius wrote on 2024-01-25, 16:27:

I got into an argument with someone at school in 1991 because I said that I wouldn't use anything but DOS on my machines. I sa […]
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I got into an argument with someone at school in 1991 because I said that I wouldn't use anything but DOS on my machines.
I said Windows was fine for some productivity, text editing, etc...but that it was mostly bloat that I didn't need.
This guy said OS/2 was superior to everything and would be the primary OS fopr home use going forward. Sounds just like all the linux people for the last 20+ years.

I do think though the longer Linux sticks around and the more evil Microsoft and Apple become that its possible it does eventually take over for home PCs.

Hm, not sure what to say. It depends who you ask. 🤷 OS/2 was technically fine if the hardware was powerful.
With v2 onwards, it did a lot of virtualization and V86 magic for DOS and Windows, for example.

OS/2 also had HPFS filesystem and a HDD cache. Such things needed plenty of memory.. We're talking about 8 to 16 MB, at least.
Even in 1987, OS/2 1.x wanted 4MB minimum for normal operation, despite being optimized in the following years.

For software developers (even at Microsoft) and other power users, OS/2 was really nice, thus.
Multitasking all sorts of tools and having all those old limitations gone (short filenames etc) was certainly a relief.

That's something that Windows had trouble with, even though it wasn't noticeable all the time.
Because, there's a difference between having multiple Windows applications loaded and them being idle and having them doing something same time.
If some user runs something akin to classic POVRay or Photoshop to render an image, the rest of Windows is basically being frozen.

But even here, OS/2 could use a trick - loading multiple copies of Windows, one for each new Windows application.
Windows NT had a similar feature later on. Downside is, that it needs a lot of memory.
And that Windows applications in separate instances can't interact which each others so well (if at all).

Games, however, were better to be run on a fast 486 with VLB/SVGA and DOS with QEMM & Cloaking software.
OS/2 Warp did better here, but it still wasn't as smooth as an optimized DOS system.

Btw, the Amiga people also acknowledged OS/2, despite being from the maker of the hated PC platform.
A bit akin to how Linux people used to like Windows 2000..

Edit: Here's a ~1992 video of S. Jobs running SoftPC emulator on a NeXT workstation.
That's the kind of environment that DOOM was being developed on.

https://m.youtube.com/watch?v=KMX_FuOLoCI

The emulator was soon available for classic Macs of the early-mid 90s (SoftWindows was based on it). SoftAT, too.

On the PC side, OS/2 was about the closest that was being available same time.
Especially version 2.x had the new ability to multitask DOS applications.
It could boot OSes located on a diskette, even. Or run ancient booter games in a window.

The one difference I can see here is reparability and replaceability. 

Yes, I think thats true. One of the questions I always ask myself is how long different components may last at most and the physical HDD is (especially if used) a real wear part.
So the majority of old PC s out there will probably have a faulty HDD and not a small percentage of people who are starting to bring these machines back to life will probably sign up here and the first question is... "how do I get my hdd replaced .."
If I would further speculate next is probably PSU, then Mobo (especially when caps are bad). On the other hand, CPU's, especially before the GHz race may last another 100 years. One more thing are cases, thats what is causing me a lot of trouble.
Newly made Retro styled AT/Baby AT Case

So I think the CF cards are an entry point into the hobby. I personally have only one single less than 500MB hdd left and I dont use it because its the last I have (of course its very usefull to chek HDD controlers etc if the cf card solution is not working - as happens quite often)