.net has random files?

I all!

I wonder how can I translate the following, simply, code to Vb.NET (and/or
C#), possibly using just the .NET framework functions instead of the Visual
Basic Run-Time Functions (e.g. FileOpen) implemented only for compatibility:

Type MyType2
Values(10) as byte
End Type

Type MyType
Dt As Date
Typs(10) As MyType2
End type

Dim x() As MyType
Redim x(0 to 50)

' write a whole file
Open "dummy.dat" For Binary As 1
Put 1, 1, x()
Close 1

' update the #10 item
Open "dummy.dat" For Binary As 1
Put 1, 10, x(9)
Close 1

And then read the values:

' read the whole file...
Open "dummy.dat" For Binary As 1
Put 1, 1, x()
Close 1

' ...or just one element
Open "dummy.dat" For Binary As 1
Put 1, 10, x(9)
Close 1

I would not think that .NET has no structured binary/random-file
capability!
And if it is... how can I obtain something similar (I need speed accessing
disk and I don't want DB-engines)?

Thank you!