Thank you very much guys for your kind input and patience.  
 
Right now the final sticking point to this "new" XP DAW is figuring out the video situation.  I really do not want/like the idea of a dedicated graphics card with massive heat sinks and/or fans just for an audio DAW.   Looking around eBay I'm confused as to what specs to target for PCIe video.....  64MB, 128MB? Brand?  OEM cards ok or not?  Ugh.... 
 
Sonic

THambrecht
To my knowledge SONAR makes NO use off the cache.
In older versions caching was disabled (recommended)
In the current aud.ini:  ReadCache=0   WriteCache=0
 

That refers to the Windows file caching system, which normally stores stuff in RAM until Windows decides it sees a gap where it has time to write to the permanent storage (HDD or SSD). Sonar, like nost DAWs, by default bypasses that and sends the data straight to disk. The original idea being that if Windows or the application crashed any just recorded stuff would be safely on the disk, not still sitting around in RAM. Many years ago one of the big plusses for Pro Tools HD hardware systems built around digital recorders storing data not the computer was that kind of protection against data loss. Also that the external box doing some of the work could take some of the strain off the computers of that era.

How relevant that actually is on a modern system is debatable, and if Windows crashes even if the data is on the drive it often hasn't got the necessary file system headers and catalogue entries to tell Windows it's there so Windows can't see it and data recovery techniques are needed to "find" it. And with caching enabled a project that fits entirely in RAM runs incredibly fast and smooth, though SSDs have caught up quite a lot even with that.

The other disk cacje, which is the one being discussed I think, is the RAM chips that are part of a disk's controller board and cache the stuff that's frequently being read or has just been written to the disk to give the disk some time to catch up and write data to the platter. It basically speeds up saving data that's smaller in total than the disk cache. Modern HDDs have pretty big caches.

SonicExplorer
Thank you very much guys for your kind input and patience.  
 
Right now the final sticking point to this "new" XP DAW is figuring out the video situation.  I really do not want/like the idea of a dedicated graphics card with massive heat sinks and/or fans just for an audio DAW.   Looking around eBay I'm confused as to what specs to target for PCIe video.....  64MB, 128MB? Brand?  OEM cards ok or not?  Ugh.... 

There are quite a few inexpensive fanless boards around, usually based on ATI chipsets. They need some air movement within the case, but the PC in my sig (now sadly deceased) ran fine with just a big Nokia cpu cooler and a couple of big 140mm Nokia set at reduced voltage for slow running one on the cpu and one as a case fan to flow air through the case - and you need a case fan anyway. That PC was almost inaudible from 8 feet, measured 26dBA usually, around 45dBA under pretty heavy loading. The gpu was OK for a lot of games and ran Photoshop pretty quickly as well :-)

Big gpu heatsinks aren't a problem other than if they block a slot you need for something else. In fact they're good because they mean no fan is needed on the gpu.

I've used OEM-style cards since the 90s and have had no more problems with them than any other.

DAWs don't really need massively powerful graphics setups. Most people in the Mac world using Retina MacBooks just have the Intel cpu on-board graphics, fairly recent MacBook Pros being HD4000 series or better. That handles anything a DAW requires perfectly well, can cope with a couple of 1080p (or better) displays, and all the optional upgrade to a seperate gpu does is make a few games run better and add heat and noise. And you might have trouble finding drivers for XP-era gpus - or XP drivers for modern Intel integrated graphics.

XP is ancient in OS terms, it was replaced a decade ago. To be honest I wouldn't go there, it's like building a 1970s car in 2017 from what spares and old stock parts you can find. I'd bite the bullet and go to at least Windows 7. Vista onwards introduced a lot of tweaking to the OS which has benefited DAWs quite a bit.

One more question....  does it matter that I'd be using SATA drives in IDE mode (in other words the MoBo is set to IDE/Legacy)?  Does that make the drives perform any worse than a native IDE drive would have?    Just wanting to make sure I'm not missing anything since I've never tried SATA drives before....
 
Thanks,
 
Sonic

In my experience SATA drives always work fine. The only time the drive is a problem for me is when I record every time I practice a tune for weeks on end. Then I hit the limit of what the thing can read. I usually go delete a few hundred useless takes and I'm rolling again.
 
I have wanted a setting where when you're tracking like this it doesn't bother reading from disk things takes you aren't listening to.
 
Someday.