1. I see a lot of stand-alones with removable hard drives. What is the main reason for this? Backup? or Playback?
It seems like a nice idea to be able to pull out the drive and go play it back somewhere. But thinking thru it, it also seems like a bit of a hassle to have to plug it into another pc or ide-to-usb converter. And even then, does windows play back the recordings or do you need some kind of application software?

2. Mobile DVRs. Looking for recommendations for a solid 4ch mobile dvr for school bus and police car use. I see there are a lot of mobile dvrs on the market, but none of them that I have seen offer a good and easy retrieval method. Any suggestions?

Bump - anyone have a mobile dvr they would recommend? or one to avoid?

I know of GE, March Networks, and then there are some OEM ones also ..

Only reason I see for removable HD is if you need extended archive capacity and you want to buy multiple HDs and library them for possible future use. Take a look at Dedicated Micros TransVu for mobile. It is an 8 channel unit with additional features so may be overkill for your needs.

1. In my opinion, removable HDD works like tapes in VCR. When one disk is full, just replace it with a new one. Moreover, you can plug them into another PC for playback.

2. It is strongly recommendded CO-1000M series Mobile DVR, see link below:
http://www.codeoutsourcing.com/pages/products/mdvr/1000m/index.php
The mobile DVR is proved working pretty stable, which is the most important criteria for mobiel applciations.
Ways to backup:
1) Using removbale disk, just as most of DVR do.
2) USB2.0 transmission port.
3) By network, wireless or ethernet. for example, in Wi-Fi area, you can just press one button to "bump" data to control center through wireless LAN.
sound interesting, yes!