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windowsoperating-systemramhard-drive
Dave F.
Dave F.

Reputation: 155

How does windows distinguishes between discs?

I wonder how windows distinguishes between diferrent drives and memory modules, I mean how can windows writte somethig specificaly to disc C or disc D. In every programming language when you declare variable it gets saved into to the memory, and when you need to store something to hdd, you have to use some library. So, how does windows handle it? Does it treat all discs and memory modules as a single line of data, and does it only save each mediums beginning adress? - like 0x00000 is where the disc C begins, 0x15616 is where the disc D begins.

Upvotes: 0

Views: 182

Answers (2)

user123
user123

Reputation: 2884

Like @MSalters said,

C: is a symlink to something like Device\HarddiskVolume1.

What it means is that disk drivers on Windows are implemented as virtual filesystems a bit like on Linux. I'll explain for Linux since there's much more documentation but the answer is quite similar for Windows even though both OSes do things differently.

Basically, on Linux everything is a file. Linux ships with disk drivers as these are at the basis of every computer. Linux exposes a driver model like every OS. The Linux driver model for files (including hard disks) exposes functions that will be called by the kernel to read/write to disk. There are open, read and write functions that the kernel expects to be present for a file driver.

If you wanted, you could write a disk driver and replace the existing one. You write drivers as modules that you can then load in the kernel using certain utilities that ship with Linux. I won't share more details as I'm not that much aware. Once your code is loaded in the kernel, it has access to all kernel code and all hardware since it runs in kernel mode.

Today, disk drivers probably use PCI DMA which is a controller connected to the PCI bus which allows to do disk operations which ignore the CPU and load disk data to RAM directly. The PCI convention says that all compatible devices (like PCI DMA controllers) must expose a certain interface to the computer. This interface is mostly some memory mapped registers that can be used to send commands to the controller. The OS will write data in these registers to tell the DMA controller to do disk operations. Then the DMA controller will trigger an interrupt once it is done. The OS will then know that the data is readily loaded into RAM and ready for use. The same applies for writing

The OS knows the location of these registers by looking in the ACPI tables at boot.

Upvotes: 1

MSalters
MSalters

Reputation: 179809

In modern Windows (2000 or later) C: is a symlink to something like Device\HarddiskVolume1. The number there can vary. Typically, \Device\Bootpartition is also a symlink to the same HarddiskVolume.

Windows doesn't use libraries to write to disk. Instead, it uses drivers. The chief difference is that drivers run as part of the OS kernel, while libraries run as part of applications.

Upvotes: 0

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