Thanks to help by David Heffernan I have a program written in Freepascal (but a Delphi solution to my question would suffice) that reads a physical disk sector by sector. It does so using the Windows API CreateFileW function for the disk handle, then FileFile, FileSeek etc to navigate and read. If all the sectors are OK, it works fine. However, if the disk had bad sectors, I need to treat them differently.
My question is, is there and procedures or libraries that can be used, while reading these sectors, to determine if they are bad sectors? If not, how might I go about it? I gather it is the disk controller that knows what sectors are bad and which are not, so I don't think my program can actually access a bad sector, so how can I detect which are the bad ones and act accordingly? Does one need to query SMART and if so, how?
I have searched this site (only found this C post, which relates to a program, not code) and Googled it and no obvious solutions came to my attention.
Sectors and their hardware status are not things that normal user-level code needs to deal with so there is no easy copy/paste API available for this purpose.
Also in general the sector concept is abstracted away on multiple levels. For one example see the Wikipedia: logical disk address translation. Physical sector status is very low-level concept. Some hardware vendors even don't expose it through public API at all. Bad (or suspicious) sectors are often detected in the hardware itself and automatically redirected to other places. So in general the bad disk-sector concept does not exist
...Bad sectors. If a disk driver encounters a bad sector, it may be able to read from or write to the sector after retrying the operation, but the sector will go bad eventually. If the disk driver can proceed, it should log a Warning event; otherwise, it should log an Error event. If a file system driver finds a large number of bad sectors and fixes them, logging Warning events might help an administrator determine that the disk may be about to fail...
If you really need to work with this low-level concepts then first forget about Pascal or Delphi as your requirements.
Learn how to use the Windows API and once you know it bind to the API in your language of choice (you can map any Win32 user-level API function to Free Pascal easily).
For understanding how user-level code sees the disk abstraction start reading documentation at MSDN → Dev Center - Desktop → Device Management Reference → Device Management Functions → DeviceIOControl function
For understanding how the kernel-level code sees the hardware and how does it communicate with user-level code start reading documentation at MSDN → Dev Center - Hardware → Develop → Drivers → Concepts for all driver developers
For example of reading S.M.A.R.T. disk information see WinSim Inc. DISKID32 source code function ReadPhysicalDriveInNTUsingSmart() in diskid32.cpp
In my opinion you are going to swim in a dark & deep waters without flashlight and swim ring and you should think twice about what you (or your users) really need/want and perhaps improve the question to get a reasonably-sized on-topic answer