CVRs - How do they work?

Would like an answer to the following question for both an analog and a digital Cockpit Voice Recorder (CVR)...

In a 30 minute continuous loop is there ever any point there is less than 30 minutes of recording?

More specifically - for an analog CVR does it continuously record over the last 30 minutes so that if you were retrieving an analog CVR you would have this stepwise time jump right where the recording stopped (i.e. 8:30/8:00) like that?

More specifically - on a digital CVR is it constantly appending to the end of the file and erasing the front of the file to where you have a constant 30 minute data file 8:00-8:30 with 8:30 appended as the last data point on the file?

If the above are wrong, will you please explain how they work?

This might help, Val.

travel.howstuffworks.com...
Most magnetic-tape CVRs store the last 30 minutes of sound. They use a continuous loop of tape that completes a cycle every 30 minutes. As new material is recorded, the oldest material is replaced. CVRs that used solid-state storage can record two hours of audio. Similar to the magnetic-tape recorders, solid-state recorders also record over old material.

So it would seem that regardless of whether they were of the magnetic tape or solid-state type, the oldest data is overwritten by the latest.

[edit: to add]

www.tailstrike.com...
Per Federal regulation, CVRs record a minimum of the last 30 minutes of aircraft operation; this is accomplished by recording over the oldest audio data. When the CVR is deactivated or removed from the airplane, it retains only the most recent 30 minutes of CVR operation. This model CVR, the Fairchild Model A 100S, records 30 minutes of digital audio stored in solid-state memory modules. Four channels of audio information are retained: one channel for each flight crew and one channel for the cockpit area microphone (CAM).

[edit on 10-2-2008 by 12m8keall2c]

Well, that makes sense. I wouldn't think on an analog recorder there would be the need to "erase ahead", but that you would simply be recording over. I mean, I can't see why they would operate to where there would ever be any portion of the tape that would be "cleared" of recording.

On the digital, even more so because you are simply appending data to the end of the file.

Those are my assumptions, but I wanted to make sure I was thinking correctly.