Physical Memory: What is it?

The answer is actually quite simple.  The video function reserves a portion of  memory to do its work.  The amount varies depending on what video software is being used.

If it is possible, consider upgrading your memory to 4GB.  Depending on whether you have a laptop or desktop and how many memory slots you have, unfortunately, that may mean you have to replace what you have.  The process of doing this is actually quite simple.  The most complex part is making sure you get the right memory.  If you will tell me the make and model of your computer, I may be able to advise you on what to buy.

Our opinions differ on links.  Repetition of what is said elsewhere ... don't get it.

(Who is "us"?  This is a peer-to-peer volunteer-based public international forum, so...)

I apologize for the Process Explorer link - I did not note (initially) that in the first sentence you wrote that was what you were using.  My bad.  Consider yourself un-perplexed.

What you quoted is not a query - it's a statement you made.  All you asked was what Physical Memory is.  That was your only question.  Perhaps it was not worded as you intended, but...

I suggest you utilize this:

RAMMap v1.5

https://docs.microsoft.com/en-us/sysinternals/downloads/rammap

Since you are into synopses, here's the synopsis posted on the page...

Have you ever wondered exactly how Windows is assigning physical memory, how much file data is cached in RAM, or how much RAM is used by the kernel and device drivers? RAMMap makes answering those questions easy. RAMMap is an advanced physical memory usage analysis utility for Windows Vista and higher. It presents usage information in different ways on its several different tabs:

• Use Counts: usage summary by type and paging list
• Processes: process working set sizes
• Priority Summary: prioritized standby list sizes
• Physical Pages: per-page use for all physical memory
• Physical Ranges: physical memory addresses
• File Summary: file data in RAM by file
• File Details: individual physical pages by file

Use RAMMap to gain understanding of the way Windows manages memory, to analyze application memory usage, or to answer specific questions about how RAM is being allocated. RAMMap’s refresh feature enables you to update the display and it includes support for saving and loading memory snapshots.

For definitions of the labels RAMMap uses as well as to learn about the physical-memory allocation algorithms used by the Windows memory manager, please see Windows Internals, 5^th^ Edition.

Good luck!

Is it so difficult to give a synopsis of what the links explain?

Do you know how often useless links are posted here?  (A LOT!)  They waste our time.  A summary of the link's content is therefore very useful for us. 

You send a link to Process Explorer.  Why?  That's what I use.  So you're recommending I use exactly what I'm using?  I'm perplexed.  Please clarify.

Next you send a link talking about memory.  It recommends using Resource Monitor but it won't even launch in my Win7 system.  I went to Run, Resmon.exe and though a window appeared it remained empty.  Perhaps I've disabled something in services.msc (my system runs rather on the lean side with a minimum of things starting automatically) that is preventing this program from operating normally. 

I like Process Explorer as it seems to give a good picture of what's going on but I often wonder about how comprehensive it's scope is.  When I use Win7's Task Manager it seems to be far more detailed though I'm not familiar with the terminology used to describe what its showing.  Ask 100 people out there what Page Faults, Peak Private Bytes or PF Delta mean.  You'd be lucky to find 1 that has a clue. 

Now back to my original post query:  "almost half my memory is being used in this mysterious Physical Memory area but I can't see which program is using it"

Does anyone have any idea about this?  Surely this isn't so difficult to explain.  Surely someone has used Process Explorer before and has run across this.

First - use this instead:

https://docs.microsoft.com/en-us/sysinternals/downloads/process-explorer

Second - read this (to look at your current concern and methodology more in-depth):

https://www.techrepublic.com/article/how-to-use-windows-10s-resource-monitor-to-track-memory-usage/

(Yes, it's for Windows 10, but the information is still generally good for you and is up-to-date.)

Third - the only question you asked:

"Physical Memory: What is it?" -- it is the actual amount of actual physical (you could touch it) RAM you have installed in your computer (the hardware.)