C# Unit-of-Work Design Pattern for Multiple Storage Types

I'm trying to implement the unit-of-work pattern for mutliple storage types like the windows registry, a database or the app.config but I cannot figure out how to do it. All examples I find use Entity Framework which already is a UoW so it doesn't help much. What I'd like to store is a simple Setting object.

From http://martinfowler.com/eaaCatalog/unitOfWork.html I understand that

A Unit of Work keeps track of everything you do during a business transaction that can affect the database. When you're done, it figures out everything that needs to be done to alter the database as a result of your work.

So I probably should start with a class that has two settable properties and one that tells me whether it's dirty and needs an update.

class Setting
{
    private string _value;

    public Setting(string name, string value)
    {
        Name = name;
        _value = value;
    }

    public string Name { get; set; }

    public string Value
    {
        get { return _value; }
        set
        {
            _value = value;
            IsDirty = true;
        }
    }

    public bool IsDirty { get; private set; }
}

then I guess I need a base repository:

abstract class SettingRepository
{
    private readonly List<Setting> _settings = new List<Setting>();

    public abstract IEnumerable<Setting> Get(Setting setting);

    public void Add(IEnumerable<Setting> settings)
    {
        _settings.AddRange(settings);
    }

    public abstract int SaveChanges();
}

and a unit-of-work as SettingContext:

abstract class SettingContext
{
    protected SettingContext(SettingRepository settings)
    {
        Settings = settings;
    }

    public SettingRepository Settings { get; }
}

Now I'm not sure where I should put all the Update/Insert/SaveChanges logic? A database would for example support transaction whereas the windows registry not.

Do I need different repositories for each storage type or do I need different unit-of-work aka contexts for each of them? I'm really confused.

I don't know what exactly I should do next. Maybe I think to much Entity Framework and try to implement it in a too similar way like this:

using(var context = new SettingContext(new RegistryRepository()))
{
    context.Settings.Add(new Setting("Foo", "Bar")); // this should be created
    context.Settings.Add(otherSetting); // this should be updated
    context.SaveChanges();
}