How does data/rate relate to multiple movie playback

[RobF]

If I have 4 movies all with a data rate of say 3MB/sec would I need a hard drive with a data rate of greater than 12MB/sec or would it need to be more as all 4 movies are playing simultaneously?

Would the 4 movie challenge be the same as playing back 1 movie with a data rate of 12MB/sec?

[samsc]

If I have 4 movies all with a data rate of say 3MB/sec would I need a hard drive with a data rate of greater than 12MB/sec or would it need to be more as all 4 movies are playing simultaneously?

Would the 4 movie challenge be the same as playing back 1 movie with a data rate of 12MB/sec?

the 'headline' data rate of the drive has very little to do with this.
the rotational speed of the drive is much more important.
as is the number of transactions per second that a drive can do.
as is the seek time of the drive.

a bog standard drive can do less than 100 things per second,
and as playing 4 movies at 25fps needs 100 completed transactions per second- ( even without any overhead )
and the seek time is around 12ms ( 12 milliseconds )
and the rotational latency of a 7200rpm drive is ( 1/ (7200/60 ) ) = 8.3ms

standard drives are shit.

standard drives dont work very well when accessing lots of small bits of data:
say you had packets of data spread around your disc and they were only 4k large, a disc could only read 100x4000 bytes per second- only 400k second.
So the effective trasfer rate when you have small records is only 400k/second.

The headline rates only work when you are reading large continuous files.

[samsc]

The headline rates only work when you are reading large continuous files.

incidentally this is a huge problem with the design of virtual memory systems.
virtual memory pages can be small only 4k in size, and these are scattered around the disc.
so the system might only be able to read in 100 pages in one second.
so the virtual memory transfer rate is only 400k/second.

[samsc]

If I have 4 movies all with a data rate of say 3MB/sec would I need a hard drive with a data rate of greater than 12MB/sec or would it need to be more as all 4 movies are playing simultaneously?

Would the 4 movie challenge be the same as playing back 1 movie with a data rate of 12MB/sec?

playing one movie at 25fps only needs 25 transactions per second

playing 4 movies at 25fps needs 100 transactions per second.

the disc is a mechanical device it takes time to move the head to get the next frame.

so no- 1 movie at 12mb/s is not at all the same as 4 movies at 25fps.

higher data rate movies - have their own set of problems.
different sub-systems in the computer get overloaded.

[samsc]

If I have 4 movies all with a data rate of say 3MB/sec would I need a hard drive with a data rate of greater than 12MB/sec or would it need to be more as all 4 movies are playing simultaneously?

Would the 4 movie challenge be the same as playing back 1 movie with a data rate of 12MB/sec?

check out the new performance tests.

[RobF]

Already have ;o)

[samsc]

Already have ;o)

Ill try to make them a little less geeky today.
This is still kindof raw data.