Windows Client Architecture

Oracle creates a directory called `orant` (for Windows clients)"
This refers to very old Oracle versions, such as Oracle7/8 or early 9i, where the default installation path was `C:\orant`.
🔄 Modern Oracle Net Services File Locations (Oracle 19c and 23c on Windows)
In "modern Oracle versions (12c – 23c)", including the Oracle 23c client for Windows, the installation path and configuration locations have changed significantly.
📁 Default File Structure for Oracle Net Services (Oracle 23c)

Component	Default Location (Full Client)	Notes
Oracle Base	C:\app\<username> or as specified during install	Default location for Oracle Home and software
Oracle Home	C:\app\<username>\product\<version>\client_1	Contains network, bin, etc.
tnsnames.ora	C:\app\<username>\product\<version>\client_1\network\admin	TNS aliases defined here
sqlnet.ora	Same as above	Controls naming methods and security
listener.ora	Not needed on client unless acting as a local server	Rarely used on clients
Environment variables	ORACLE_HOME, TNS_ADMIN	Can override default config file locations

🔧 If you set the `TNS_ADMIN` environment variable (or registry entry), Oracle looks there for config files instead of the default location.
✅ How to Install a Windows Client for Oracle 23c (OCI Database)
Here is a step-by-step process tailored for Windows users connecting to an Oracle 23c Autonomous Database or standard Oracle Cloud Infrastructure DB:
🛠️ Option 1: Use the Oracle Instant Client (Recommended)
🧾 Steps:

1. Download the Instant Client:
   • Go to: Instant Client
   • Choose "Microsoft Windows x64" and download at minimum:
     • instantclient-basic-windows.x64.zip
     • (Optionally)instantclient-sqlplus-windows.x64.zip for SQL*Plus
2. Extract ZIP to a Folder:
   • Example: C:\oracle\instantclient_23_3
3. Set Environment Variables:
   • PATH: Add the extracted folder (e.g., C:\oracle\instantclient_23_3)
   • (Optional) TNS_ADMIN: If you store tnsnames.ora, set this to the folder path containing it
4. Place Network Files (if needed):
   • Create and place tnsnames.ora and sqlnet.ora in the network\admin folder (or the folder pointed to by TNS_ADMIN)
5. Connect Using Tools:
   • Use SQL*Plus, SQLcl, or Oracle Data Pump
   • Syntax: sqlplus username/password@tns_alias or sqlplus username/password@"(DESCRIPTION=...)"

1. Download Full Oracle Client for Windows:
   • From Oracle Technology Network
   • Choose "Oracle Database Client (x64) 23c"
2. Run Installer:
   • Choose installation type: Administrator, Runtime, or Custom
   • Set Oracle base (e.g., C:\app\yourname)
   • After install, default config files are placed in network\admin
3. Configure Network Files:
   • Edit tnsnames.ora, sqlnet.ora as needed
   • Use Oracle Net Configuration Assistant (NetCA)

• Download Wallet from OCI
• Extract and copy the wallet files (including tnsnames.ora, sqlnet.ora) to your TNS_ADMIN directory
• Connect using:

        sqlplus admin@yourdb_high
      

✅ Summary

Task	Oracle 11g R2 (Legacy)	Oracle 23c (Modern)
Default install directory	C:\orant	C:\app\\product\23c\client_1
Config file folder	C:\orant\network\admin	C:\...\network\admin or TNS_ADMIN
TNS Resolution	Fixed path	Environment-variable based
Client type preferred	Administrator	Instant Client (ZIP)
Cloud support	N/A	Yes (with Wallet)

The "Optimal Flexible Architecture (OFA)" principles still apply in Oracle 23c, including on Windows systems, but with a few modern refinements.
✅ Oracle 23c: ORACLE_BASE and ORACLE_HOME on Windows
Oracle 23c continues to follow the OFA standard, which separates:

• ORACLE_BASE: The top-level root directory for all Oracle software.
• ORACLE_HOME: A subdirectory under ORACLE_BASE that contains the actual Oracle binaries for a particular release.

📁 Typical File System Layout for Oracle 23c on Windows
Assuming a fresh installation with no prior Oracle software, this is the default structure:

Variable	Default Location (Windows 64-bit)	Purpose
ORACLE_BASE	C:\app\<username>	Root directory for all Oracle software for the user
ORACLE_HOME	C:\app\<username>\product\23c\client_1	Specific Oracle product home (e.g., client_1, dbhome_1)
TNS Config Files	C:\app\<username>\product\23c\client_1\network\admin	Location of tnsnames.ora, sqlnet.ora, etc.

🔹 In contrast to pre-8i systems where everything lived under `C:\orant`, Oracle now aligns with OFA for cleaner multi-version management and easier upgrades/migrations.
🛠️ When Does the Default Change?

• If other Oracle versions exist, the new install may use a different subdirectory like:
  

  C:\app\<username>\product\23c\client_2
  

  or a user-defined path.
• You can override ORACLE_BASE and ORACLE_HOME during installation if needed.

✅ Summary

Feature	Legacy (pre-8i)	Oracle 23c
Single Root Directory	C:\orant	❌ No longer used
Follows OFA	❌	✅ Yes
ORACLE_BASE	N/A or hardcoded to C:\orant	C:\app\<user> (or user-defined)
ORACLE_HOME under ORACLE_BASE	N/A	✅ Yes
Multiple versions supported cleanly	Difficult	✅ Fully supported

Oracle 23c adheres to the OFA model, and the principle that "`ORACLE_HOME` is under `ORACLE_BASE`" still holds true.

Again, take care never to touch any of the files in c:\orant except the configuration file in the \network\admin directory. You can edit these files manually in MS-Notepad, or you can use the SQL*Plus products to maintain them. The next lesson discusses how to use SQL*Net Easy to add an entry to your tnsnames.ora file.