If at least part of the purpose is to give someone experience with building a system, I'd suggest going for something that at least physically resembles the modern system as much as possible, so:
- (u)ATX form factor
- ATX PSU and connector, preferably with ATX12V as well so he learns not to forget that
- socketed CPU, not slot
- DIMMs of some description or other, preferably dual channel.
- SATA would be better than PATA.

Also, it needs to support that 500GB SSD at a hardware (BIOS) level.

Now, challenge there is that ATX12V and 500GB storage support contradicts your requirement for ISA and DOS. Tbh. I don't think that adressing and interrupts are remotely relevant even for a power user on a modern system, so unless he wants to start low-level developing, I'd drop them. To me, it sounds like an So478 P4 or So754/939 Athlon64 (which even phyisically resemble a Ryzen) would be the best option, particularly as they can be sourced dirt cheap. If you want DOS compatibility with not too many compromises, make sure the chipset can do DDMA. That means you can go up to P4 with ICH5, which means a dual-channel i865 build would fit the bill, and you have SATA. For educational purposes that would be about the sweet spot I'd say, and those things are cheap too.

Conversely, if you want to teach what each component does, even if the equivalent has long been integrated into other bits, nothing beats an old BX-era system. I used that for my eldest two children, in no small part because a 6-year old hands are less likely to mess up a slot CPU than a socket. My son in particular has picked up most of it and is getting very confident around hardware and software, correctly identifying bottlenecks and hacking away at .jar files for Minecraft mods aged 8 😀

dionb wrote on 2021-05-29, 23:58:

Now, challenge there is that ATX12V and 500GB storage support contradicts your requirement for ISA and DOS. Tbh. I don't think that adressing and interrupts are remotely relevant even for a power user on a modern system, so unless he wants to start low-level developing, I'd drop them.

In this case, it's more me just wanting to give him a basic enough familiarity with the concept of them. He's eventually gogin to be getting certs for advancement, so I thought it would be useful. I would also be more than willing to grab a PCI card to circumvent the LBA issues outside of DOS, where I would probably be using an SD-IDE converter. Thanks for catching the lack of explanation, though.

dionb wrote on 2021-05-29, 23:58:

To me, it sounds like an So478 P4 or So754/939 Athlon64 (which even phyisically resemble a Ryzen) would be the best option, particularly as they can be sourced dirt cheap. If you want DOS compatibility with not too many compromises, make sure the chipset can do DDMA. That means you can go up to P4 with ICH5, which means a dual-channel i865 build would fit the bill, and you have SATA. For educational purposes that would be about the sweet spot I'd say, and those things are cheap too.

I will definitely keep that in mind.

No, don't show him anything if he's tryna get certs, 20% of the stuff is theoretically right, but practically wrong 😁

All that is going to be TOO old for teaching modern systems builds. Modern systems have high focus on airflow, CPU cooling and proper cabling.

You will want something like an old Core 2 or Core i3 system, as a minimum, if you want to teach building modern systems.

They are cheap, have the LGA sockets many modern systems use, and use PCI-e style hardware like modern system.

canthearu wrote on 2021-05-30, 02:15:

All that is going to be TOO old for teaching modern systems builds. Modern systems have high focus on airflow, CPU cooling and proper cabling.

You will want something like an old Core 2 or Core i3 system, as a minimum, if you want to teach building modern systems.

They are cheap, have the LGA sockets many modern systems use, and use PCI-e style hardware like modern system.

It's partially to give perspective, 🤣. I have become a lot better at cable management and airflow since having to work with ribbon cables and single-header fan systems.

BetaC wrote on 2021-05-29, 23:29:

First and foremost, the purpose of this build will be to give my brother-in-law firsthand experience with putting together a system that works. He has plans for building a modern system for himself, and I feel that having experience with building something that he won't feel guilty about potentially messing up would help keep him from overthinking things when that day comes.

Agree with canthearu !!
I think you should find a cheap i3 or i5 from a thrift store made more than a few years ago (say a Dell Vostro 200, Dell Optiplex 7010 or anything similar). Make sure it works then take it apart. (last one cost me less than $50)
One thing about some Dells is they are no different than buying a case, psu, mobo, ram, etc AND a very inexpensive way to educate someone on building a decent newer ATX machine.
Have him re-assemble it like it was all new parts and hope it works. Once he grasps the aspect of a simple"made for" build you can point out the differences between it and varied parts bought online.
Did that for my brother a few years ago (ok maybe 10) and he is actually quite good at building a new system now when he wants too.
added: OK the 7010 have gone way up since I bought one, now are $100 and up. The idea is still valid though. Find a cheap one !!
added2: forget the airflow stuff and cable management as that will detract from actually learning the basics of a basic first build until he gets the whole build it thing down.
That comes later...

Horun wrote on 2021-05-30, 03:24:

(last one cost me less than $50)

This is my reason behind saying something like the Core 2. They are so silly cheap at the moment, if he breaks it, it isn't going to hurt.

Unlike actual retro hardware, that is become more expensive and difficult to find.

canthearu wrote on 2021-05-30, 03:32:

Horun wrote on 2021-05-30, 03:24:

(last one cost me less than $50)

This is my reason behind saying something like the Core 2. They are so silly cheap at the moment, if he breaks it, it isn't going to hurt.

Unlike actual retro hardware, that is become more expensive and difficult to find.

Got it ! You explained very well

I agree with others here and suggest Athlon 64 or newer (cheap, fundamentally similar to modern hardware, transfer certain components to modern build, etc).

I don't mean to offend, but just would like to pose the questions:

• If your brother-in-law is the end user of the practice computer, what does he actually want to use this system for (besides learning)?
• What aspects of this practice build experience will your brother-in-law actually appreciate when it comes time for him to build a modern system?
• If you are willing to put him in the center of this activity, do you need to be sneaky?

You suggested that your brother-in-law doesn't care to play DOS games... If you make him learn to configure interrupts for ISA cards, will he thank you for that? Maybe another way to provide 'perspective' is after you help him build his practice computer you can show him some of the highlights of your collection. IMO if he has asked for your help, he respects your expertise already and you don't need to work too hard to impress him. 😀

bZbZbZ wrote on 2021-05-30, 05:09:

I agree with others here and suggest Athlon 64 or newer (cheap, fundamentally similar to modern hardware, transfer certain compo […]
Show full quote

I agree with others here and suggest Athlon 64 or newer (cheap, fundamentally similar to modern hardware, transfer certain components to modern build, etc).

I don't mean to offend, but just would like to pose the questions:

• If your brother-in-law is the end user of the practice computer, what does he actually want to use this system for (besides learning)?
• What aspects of this practice build experience will your brother-in-law actually appreciate when it comes time for him to build a modern system?
• If you are willing to put him in the center of this activity, do you need to be sneaky?

You suggested that your brother-in-law doesn't care to play DOS games... If you make him learn to configure interrupts for ISA cards, will he thank you for that? Maybe another way to provide 'perspective' is after you help him build his practice computer you can show him some of the highlights of your collection. IMO if he has asked for your help, he respects your expertise already and you don't need to work too hard to impress him. 😀

Yeah, as I have thought about it a bit more, I will probably just show some of the weirdness of DOS at a separate point. Posting the thread was as much getting the idea out as it was asking for help. When it comes to stuff like this, I have issues with getting lost in my own head for like ten revisions of an idea. I am definitely thinking about the middle Athlon era hardware though, as it would also give him hardware that will allow for some games to be played without modern issues while still allowing for things like GoG releases to work.

As for the "sneaky" bit, I meant it in the sense that once everything is said and done, he will have a working case, power supply and storage for a modern build being given as a gift. He is also mostly unaware of this being thought about, beyond my sister knowing that there's going to be a small project.