Question about Playstation memory?

a). Capacity on the label is a rounded number;

b). Some space is reserved for system files.

Yes. Almost all hard drives, not just PS4 hard drives, ALL hard drives, even flash drives have slightly less memory than advertised.

Because your operating system and various programs are taking up the space...

This seems fairly typical for consoles for a couple of reasons.

1) Storage Drives are sold using "commercial units" (where 1 TB = 1,000 GB), which are done in base 10.  HOWEVER, computers & other electronic devices run on base 2, where 1 TB (or 1 TiB, to be precise... but it's rarely utilized in public) = 2^10 GB (GiB) or 2^40 bytes.

This causes roughly a 7% difference in storage, dropping you down to ~931 GB of actual storage space.

2) System OS is stored on the drive as well...  This would include all the necessary files, updates & cache (for temporary files).  This amount will vary, but can easily eat up a couple of GB's normally.  HOWEVER, PS4 reserves 93 GB's upon some quick research...  which I'm a bit skeptical as that's based on the 500 GB system, which has 407 GB's available... but the actual storage space would be ~465 GB's... Placing the OS to a more realistic 58 GB's (with the other 35 GB's lost from unit conversion).

This would account for up to 162 / 1000 GB's of space (under the most relax figures), so there may be some preinstalled stuff to make up the remaining 17 GB's... but I'm only doing some logical legwork here with known & provided info, so there's bound to be some errors (mostly the OS storage requirements), but I hope this sheds some light on the subject.

Normal for PS4 very very

It's normal.

A 1 TB hard drive has a formatted capacity of around 931 GB, mainly due to the differences between how they're sold (where 1TB is 1 trillion or 10^12 bytes) and what computers think a TB is (which is 2^40 or about 1.1 trillion bytes)

The rest is unusable because the PS4 reserves about 10-12% of an internal hard drive for its own use, which reduces it to around 820 GB.

Yes this is normal. There are a few reasons why. Reference this article: https://www.lifewire.com/drive-storage-capacities-... they can explain it better than I can.

This happens on every single device that has storage, like a laptop, desktop, phone, tablet, etc. It isn't limited to just consoles.

thats just due to the way drives are rated .. a drive of any size will always have less than its advertised capacity by a certain percentage ..so hard drive manufacturers market drives in terms of decimal (base 10) capacity in other words a gigabyte is 1000mb .. but in actuality as read by a machine a gigabyte is 1024mb ..

Yes it’s normal. 

It might say 1 gb but in reality it can be more or less. 

You might start with 1 gb but as soon as you format the hard drive, you lose some. 

The 180 gb or so is reserved for the operating system.