Looking at new computer setup. I have always used 2 hard drives (one for the OS and programs, one for audio). Seems that nowadays everything is going to an SSD & a normal hard drive. The typical (affordable) SSD's seem to be 128 or 256 gb. My current OS/Program drive is 634 gb worth of stuff. How are people making these small SSD's work? Am I doing something wrong? 
I do store my finished mixes (WAV and MP3) on the OS/Program drive. I'm wondering if that should be on my Audio drive along with all my Cakewalk Project files? Also, my Program Data > Cakewalk > Command Center > Downloads folder is HUGE!
Any advice?
PS
I'm very tempted to just buy a computer with one HDD and then add another HDD for Audio Files just like I always have done in the past.

I have a 500GB Samsung EVO 850 SSD and a 2TB hard drive.  I have Win 10 and programs (both DAW and regular PC programs) on the SSD (339GB used) but I have my Sonar projects on the 2TB hard drive.  All my "completed" Sonar sessions (mixed down masters) are also on the 2TB hard drive.
 
Many new PC's (commercially built such as Dell, HP, etc) now come with an M.2 SSD (generally 128 or 256 GB) and a hard drive.  Most programs, data storage, etc is on the hard drive.  

I wouldn't go any smaller than 256.  That is what I have in my laptop and all of my data and most of my programs are on my 1Tb data drive.  However, it takes diligence to maintain a system like this as almost all programs want to default to the OS drive and some won't allow you to change this.
 
If you can swing it, 500 Gb is probably the way to go nowadays.  You might also consider storing your projects on an external drive.  USB3 is plenty fast enough.  Or alternatively, if you have a tower, add another standard hard drive.  1T & 2T are fairly cheap.

I think this depends a lot of what you plan to do. If you plan to buy large sample libraries then I would get the largest SSD's you can. Notice I have 3 of them in my sig and I'm going top need another one. Sample libraries being the main culprit.
At one time it was a common suggestion to buy a smaller HDD for the OS and use SSD for the samples and storage. The reason being retrieval times are not as necessary on the OS drive and more important when pulling from a sample library. While this works ok you are still buying a mechanical drive more prone to failure if you buy an HDD for the OS drive. For this reason I like to keep everything in the SSD realm.
 
If only loading  medium sized daw mix downs with few samples as whole projects, any outboard storage drive will probably be ok so long as the project can be pulled onto a faster drive later. If loading lots of synths that want to reside on C drive, then a larger C drive is a must.
 
Many MOBOs have accommodation for multiple drives. At least four or more. Since the  500g SSD drives cost less than the larger SSD drives, it makes sense to use many smaller drives as opposed to one huge drive. In this way if you experience a failure on one drive you won't loose everything. I think it also makes sense to store very important things you value on a drive that powers down and in this way reduces the time the drive is online thereby reducing failure rates and the possibility of loss. Of course you can't do that with a sample drive you regularly use. In my case it's not difficult to simply add another drive. Buy it, plug it in and away you go. I keep one drive as primarily a storage drive and the other as a sample drive....but as others have already mentioned, lots of programs default to C drive folders. You should be able to re direct the folders and point the program to them. The C drive tends to get filled up with junk over time anyway and you need to be careful when cleaning house because you could delete something important. This is why I like to err on too much space instead of too little.
 

I did this post a while ago which goes into a little detail of how to analyze your drive and make junctions. I use a 256GB for my OS, and keep it roughly 50% full. Most of the space consumed on a drive are data files (audio/video), downloads, and the old version of Win10 (if you have not scraped that off). First step is to use a utility to analyze your drive allocations so you can see what is where, then you can get into junctions or deleting/moving things that just take up space.
 

If you keep the boot drive as clean/lean as possible (which also helps for backups), you can easily get by with a 250GB SSD.  You can fit a lot of programs/plugins in 250GB space.  (Not talking about large accompanying sample-libraries - put those on a dedicated drive)
 
FWIW, I'd want a 3rd drive dedicated to mixed-down Wav and MP3 files... so they're not taking space away from your "Audio" drive.  Note that conventional HDs start to slow down as they reach the ~2/3 full point.

Thanks for all the info! 
Yes, I am talking about a desktop, not a laptop. No, I do not use a lot of samples or sample libraries. 
I am probably leaning toward 2 or 3 standard hard drives since they are quite a bit cheaper than SSD's.
 
I am experiencing something very strange when trying to check the size of files on my current drives. When I right click > Properties on a file it will sometimes show that file to be 634 gb. Then, if I close that and do it again, it will show a MUCH lower size, like 15 gb or 25 gb or whatever. Then if I move to the next file, the same thing happens. And so on. This 634 gb file size is randomly showing up, then going away on random files! Has anyone else ever seen this. What could it mean?

For displaying your current disk and folder usage, I have found the free WinDirStat indispensable.
 
https://windirstat.net/
 

WinDirStat is a free and open-source graphical disk usage analyzer for Microsoft Windows. It is notable for presenting a sub-tree view with disk use percentage alongside a usage-sorted list of file extensions that is interactively integrated with a colorful graphical display.

 
I would recommend putting Windows, all programs (except content), and plugins (except samples), on your main system drive, using an SSD at least 250GB.  I keep mine at around 50% used this way.
 
This provides for very snappy performance of boot, program launch, project opening, etc., without any lag. 
 
HDDs are fine for audio files, projects, content, samples, etc.  The use of a 2nd or 3rd drive is up to personal needs and preferences. 
 
The use of any available program and plugin installer options to locate content and sample libraries on a secondary drive at install time is the best way to keep this stuff off of your primary SSD drive.  For example, Native Access and the XLN Online Installer have options to set up the paths for you.  Cakewalk has content path options as well.
 
Then the use of directory junctions is the recommended route for installers that won't cooperate with you and insist on dumping everything on the C: drive.  Directory junctions will let your application think the data is still on the C: drive, but the directory junction tricks it with a type of shortcut that points to the actual location. 

250gb SSD-
https://www.newegg.com/Product/Product.aspx?Item=N82E16820250086
500gb SSD-
https://www.newegg.com/Product/Product.aspx?item=N82E16820250087
 
100% more storage for 1/3 more cost. The Samsungs are slightly more. WD and Samsung both get about the same ratings on Newegg.

Those are both excellent deals.  If it were me (and it would be me if my system weren't 7 years old and I wasn't planning on buying a new one next year) I'd get the 500Gb one.  I'd even consider picking up the 1TB one for $189 for samples if I used a lot of them.