Periodic test needed for external RAM?????

while POWER ON the system i am checking External RAM memory.... but i am not checking the external RAM periodically.....whether the periodic test is needed are not????

It's usually not necessary to check the RAM. For applications that require additional safety, options like ECC RAM exist. Also, if you do check the RAM, you'll need to handle a failed test, too. What is the device supposed to do if it detects that the contents of its RAM have become corrupted?

What is more important is that on any failure (RAM isn't the only thing that can break), the device in question fails gracefully and doesn't kill people or do similarly bad things when it dies.

while POWER ON the system i am checking External RAM memory.... but i am not checking the external RAM periodically.....whether the periodic test is needed are not????

It's usually not necessary to check the RAM. For applications that require additional safety, options like ECC RAM exist. Also, if you do check the RAM, you'll need to handle a failed test, too. What is the device supposed to do if it detects that the contents of its RAM have become corrupted?

What is more important is that on any failure (RAM isn't the only thing that can break), the device in question fails gracefully and doesn't kill people or do similarly bad things when it dies.