Can I change the guts of a Dell D400 Laptop?

If so, how can I do so? And can you give me some ideas for what products to go for?

This is a serious question. Why am I thinking about retrofitting a Dell D400? Because I simply like the chunky design of it. And it is also very portable. There aren't many 12' laptops out there that fit my taste.
 
No.
Of the several dozen laptops that have passed though my hands....there were no two that I could take a motherboard out of and put into a different shell.
Between different brands, or the same brand in different model lines.

Screw hole locations, I/O port locations, cooling situation...all different.
Your Dell D400 is merely a plastic shell.
 


Desktops have mainly standardized parts. I run an Ivy Bridge in my main rig. I can easily swap out my motherboard CPU for a Skylake one fairly comfortably and quickly. My 7970 GHz edition card is 3 years old, but I can put in a new 980ti tomorrow in about 5 minutes if I need to. That's the nature of a desktop build and one of its strengths.

Laptops, on the other hand, are extremely proprietary due to the customized nature of the construction and the necessity for very small form factors, etc. And given the nature of a market without interchangeable parts, even if you could retrofit an old laptop completely, you'd actually not save any money compared to just buying the new laptop with the parts.

 


If you mean more than the standard 128 MB it comes with, the D400 supports up to 2 GB RAM. You can find RAM for that for like $15-$20 on the internet.

Now, will it improve your performance? Only if your current issue is only that you are in fact running out of RAM. The reality is that the laptop is now 10-12 years old (depending on which D400 you have) and realistically there's not much you can do to push that laptop's performance very far.
 
I read that there exists RAM bypasses for the 4gb limit on 32bit machines.

The D400 has a 2gb limit. I'm not planning on using Windows or MacOS on the D400 though and even that put aside, is it possible to bypass the 2gb RAM limit on the D400 while running windows?
 


Using PAE mode is kind of janky,

I highly doubt you'll be able to get that motherboard to run more than it supports and I even more greatly doubt that you would even see any real-world benefit if you did.
 
Some applications require more than 2 gb RAM or can take up more than 2 gb ram.

So what is the PAE mode? Does it apply to linux-type OS? I'm not well versed in technology so forgive me for the ignorance I show.
 


https://msdn.microsoft.com/en-us/library/windows/desktop/aa366796(v=vs.85).aspx

What application that requires more than 2 GB of RAM are you trying to run? I can't imagine an application that actually utilizes a minimum of 2 GB of RAM running well on a decade-old laptop CPU that was designed to run programs that ran on a laptop with 1/16th the memory.

You can reinforce a horse-drawn carriage to make it strong enough to hold two tons, but it won't make your horse be able to pull it.