Record with variable number of columns?

This sounds like a really simply one-to-many relationship.

For SQL Server, I would write this like:

CREATE TABLE Devices
(
    DeviceID INT
    , DeviceName nvarchar(255)
);

CREATE TABLE Cards
(
    CardID INT
    , CardName nvarchar(255)
    , DeviceID INT
);

CREATE TABLE Ports
(
    PortID INT
    , PortName nvarchar(255)
    , CardID INT
);


INSERT INTO Devices VALUES (1, 'Test Device 1');
INSERT INTO Devices VALUES (2, 'Test Device 2');
INSERT INTO Cards VALUES (1, 'Card 1 in Test Device 1', 1);
INSERT INTO Cards VALUES (2, 'Card 2 in Test Device 1', 1);
INSERT INTO Cards VALUES (3, 'Card 1 in Test Device 2', 2);
INSERT INTO Cards VALUES (4, 'Card 2 in Test Device 2', 2);
INSERT INTO Ports VALUES (1, 'Port in Card 1, Device 1', 1);
INSERT INTO Ports VALUES (2, 'Port in Card 2, Device 2', 4);

SELECT *
FROM Devices;

SELECT *
FROM Cards;

SELECT *
FROM Ports;

This allows a Device to have multiple Cards, which in turn can have multiple Ports.

The results:

The 3 tables can be JOINed together like this:

SELECT DeviceName, CardName, PortName
FROM Devices 
    INNER JOIN Cards ON Devices.DeviceID = Cards.DeviceID
    INNER JOIN Ports ON Cards.CardID = Ports.CardID
ORDER BY DeviceName, CardName, PortName;

If you use LEFT JOIN like this:

SELECT DeviceName, CardName, PortName
FROM Devices 
    LEFT JOIN Cards ON Devices.DeviceID = Cards.DeviceID
    LEFT JOIN Ports ON Cards.CardID = Ports.CardID
ORDER BY DeviceName, CardName, PortName;

you get these results:

This is an image showing the table relationships: