In recent two years, there has been a wide variety of various vehicular hard drive video recorders (Mobile DVR) 
on the market.
As the segment market of traditional embedded hard disk DVR, vehicular hard drive vidoe recorder (defined as Mobile DVR) has won the adoration from lots of security enterprises. 

Four questions need to be asked when you purchase the mobile dvr:

Mobile DVR in the security industry can not really be said as a new product of the times, but when mentioning the technical content, I am afraid that only the people who have actually done mobile dvr can realize that. 

First question, what's the difference between mobile dvr and ordinary hard disk video recorder?

Ordinary hard disk video recorder (Ordinary DVR) uses 220V A/C current and stability of voltage and current  are relatively good.
Furthermore, due to the fixed position and environment for ordinary DVR, there is relatively little chance of vibration.
Therefore, anti-vibration function of the ordinary hard disk video recorder can be negligible.
However mobile dvr is different. Firstly, the voltage and current on the vehicle can not be understood according to conventional thinking.
The voltage of the vehicle is 12 / 24V, but in fact, 12V on the vehicle is impossible to supply stabilized 12V 
and 24V on the vehicle is also the same.
So it is important for the power board's design and many aspects should be taken into account when the 
power board is designed. 

Second question, how to design a power supply of the mobile dvr? 
To ensure that mobile dvr is working properly, firstly, we must ensure that output power of power supply board should be stable.

Under the environment of a fixed narrow voltage, due to that the input voltage and current are basically stable and moreover in terms of the electrical, output power determines the input power,
the ordinary DVR only requires an adapter in terms of power supply. An adapter is nothing less than a transformer 
plus a filter circuit, if with a little bit of conscience, plus a protection circuit, if heartless, protection circuit is not loaded. That is for cheap purpose.
Therefore, the costs and maintenance costs of ordinary DVR are relatively low.

But for mobile dvr, the first thing to do is narrowing down and doing refinement of dynamic voltage and current. How 
to ensure vehicle mobile DVR works normally? Stable voltage and current are very important.
But on the other hand, the input power of the device is fixed.
According to W = U * I, it shows that when the voltage is changing, the current is also changing and change direction the voltage and that of the current are always opposite.
So if starting voltage is designed to be low, the starting current will be relatively increased. It is so simple in macro aspect, but to realize this function in stability and ensure the device's normal working, it may require a trip from 
the city.
The first is the protection circuit's design. As is known, the power board of mobile dvr will be subjected to hundreds of times the impact within one hour.
If protection circuits is not designed well, ranging from the damage of power board, even the direct breakdown of the power supply board and burnout of motherboard. 

Third question, how is the anti-vibration function of mobile dvr designed?

Mobile DVR's anti-vibration design is very important. Frankly speaking, that is how to protect the hard disk. Because current hard disk is mechanical shaft drives.
Only a few micrometers there is between the head and the disk, if seen by naked eyes, the head is attached to the disk.
But even if you do not understand the hard disk, you should understand that 5400 rPM hard drive will be rotated 
at least 90 times per second and if the head is attached to the surface, and before long, the head gets grinding 
and will be gone.
In so close distance, if the effect of anti-vibration is not done well, as long as there is a little wobbling for the head, ranging from damage of hard disk to the crash of the head (hard disk terminology).
So anti-vibration of hardware is very important. 

Fourth question, how are the fault-tolerance and error correction functions of hard disk designed?

Answer: Since hard disk emerges, there has been a difficult problem that needs to be solved both in IT hardware industry and software industry in terms of hard disk's fault-tolerance and error correction capability. 

For an embedded system, if you want to do perfect design in terms of fault-tolerance and error correction, it is very difficult! But for the design intent of an embedded system, embedded system is originally designed and also has always been pursuing better stability and speed of execution.

But a problem that can not be ignored is that portability of embedded system is poor, resulting in that once designed, 
it is impossible to have too big changes. So it is very important for the ideas of first design. Regarding embedded system, in terms of hard disk's fault-tolerance and error correction, currently, the effective way is its reading and 
writing control ability.