What is the difference between Windows and System folders?

(Windows was released on November 20, 1985. Today it turns 25. Happy birthday!)

In the Windows API from the very beginning there are two separate functions GetWindowsDirectory and GetSystemDirectory . Why was not enough alone? Both of these system folders are write-protected, both are included in the PATH and DLL search list. Why was they separated?

Aksakals will remember that in those old times the purpose of these folders was different. The Windows folder was writable, and it was in it that all user settings were stored. For example, the GetProfileInt function reads from the WIN.INI file in the Windows folder, and the GetPrivateProfileInt function if the full path of the INI file is not specified, by default it works with the Windows folder.
In those old days there were no separate folders with user profiles; in the Windows folder, in fact, the profile of a single user was stored in the system.
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On the other hand, most of the Windows system files were stored in the System folder, and this folder was read-only. Even if there was no mechanism that actually forbade writing to this folder, Windows itself never wrote to it (except for installing and uninstalling applications, and other system setup operations).

Splitting system files into two folders allowed Windows to work in several different configurations.

Traditional

On the local disk of each computer (on a diskette, and for the rich, on the hard disk) there is a Windows folder, and in it is the System folder. Most Windows users worked this way. Although in this case nothing prevents the user from writing to the System folder, Windows does not write to it during normal operation.

Stitched in ROM

On the local disk of each computer is a folder of Windows, and in the ROM-disk - the folder System. ROM-disk - this is a virtual disk, the contents of which is not stored in RAM, and stitched in ROM. Users of smartphones and communicators hardly need to explain in more detail what it is; and the rest can imagine a flash drive, forever write-protected.
Since the contents of the System folder never changed anyway, its firmware in ROM allowed saving valuable disk space or (especially!) On a hard disk.

Network

The local disk of each computer contains the Windows folder, but it has network drivers (stupid, wonders what!), And AUTOEXEC.BAT connects the network drives from the central server, which is supported by the IT department of the company. This network drive might look like this:

M: \ SYSTEM	Windows system files
M: \ WINWORD	installed Word for Windows
M: \ 123	installed Lotus 1-2-3
...	etc.

Folders of this network drive are read only. All computers in the company are connected to the same drive, and therefore use the same physical files on the server - both as part of the Windows system files, and as files of installed applications. If the IT department needs to update or reinstall the application, they can simply disconnect everyone from the server (or, if they are more polite, then wait until they all come out by themselves), allow writing to the M :, disk, update or reinstall the necessary application, and reconnect M: read only. When users come back - slam! - A new application is ready to launch on their computer.

Fully networked

The computer boots from a ROM disk, from a floppy disk, from a local hard disk, or over a network. When booting, it connects network drives on which both the Windows folder (its own for each user) and the System folder (one for all) are located. From now on, Windows is fully networked: user files are saved to the Windows folder on the server, system files are read from the System folder on the server, and even calls to the paging file go to the server. This configuration is usually called a diskless workstation : after Windows is loaded, local disks are no longer used.

The observant user will notice that in Windows 1.x / 2.x there was no System folder at all : it appeared only in Windows 3.0. What does Raymond mean?

As you can see, it was not initially required that the System folder be located inside the Windows folder, or that one of these folders be located on the boot disk. I guess now Windows no longer supports most of the listed configurations. But at least you now understand why the Windows and System folders were separated.