A lot of it is down to the quality of the hard drive. Probably why your laptop is fine, but workstation isn't.
Disks have a maximum read/write rate. Cheap ones have a low rate, more expensive ones are higher. If you have a very cheap or crap drive, even background windows tasks can use up much of that rate, leaving nothing for you to actually do anything with.
My parents PC was almost unusable, due to the hard disk constantly being at 100% capacity. It wasn't that the computer (or windows 10) was actually doing much, it was just a cheap, crappy hard disk. I got them a much higher quality one of the same size, and the computer now works fine.
Unfortunately it's a consequence of pushing the price down whilst keeping the eyecatching "1 terabyte hard disk!" marketing stuff. Yup, its got a 1TB disk, just the crappiest one they could find! Dell is really bad for this at the moment, but it's the same with most other manufacturers and anything considered 'budget' (ie. below about £800...)
@Steve (sdh2903), Rhett is probably right. It might take some resoldering to replace the unit. The laptop almost certainly won't have a sata slot for a normal hard drive, as it would take up too much space. Using an SD card is probably your best bet.