Tuesday, Nov 8, 2005
There seems to be a bit of confusion about Blu-ray's read speeds in
comparison to DVD's read speeds specially given the Xbox 360's 12x DVD
rating. I am going to attempt to clarify the differences.
The first
difference that should be noted in a DVD vs Blu-ray discussion is that
DVD's are Constant Angular Velocity (CAV) and Blu-ray is Constant
Linear Velocity (CLV).
CAV: The drives transfer rate is
variable. Information on the inside tracks of the disc is read at
approximately half the speed as the information on the outside of the
disc.
CLV: The drives transfer speed is linear or
constant regardless of whether information is on the inside tracks of
the disc or the outside.
This is important to note because each of DVD's X ratings have a minimum and a maximum read speed and the advertised read speed is taken from the maximum, consequently a DVD drives maximum read speed is almost never realized. On the other hand Blu-ray's only has one constant read speed:
Another
important note about CAV drives (e.g. DVD) is that because information
on a disc is written from the inside to the outside the X rating is
never realized unless the disc is entirely full.
Example:
The maximum read speed of a disc that is only half full on a
12x drive is only 12MBps compared to the drives maximum of 16.5MBps.
The comparison
Mb = megabits
MB =megabytes
Blu-ray 1x: 36Mbps / 4.5MBps
12x DVD: 66 - 132Mbps / 8.2 - 16.5MBps
Blu-ray 2x: 72Mbp / 8MBps
12x DVD: 66 - 132Mbps / 8.2 - 16.5MBps
Blu-ray 3x: 108Mbps / 13.5MBps
12x DVD: 66 - 132Mbps / 8.2 - 16.5MBps
Blu-ray 4x: 144MBps / 18MBps
12x DVD: 66 - 132Mbps / 8.2 - 16.5MBps
At 2x Blu-ray can read as fast as 12x DVD's minimum read speed. At just
3x Blu-ray is comparable to DVD at 12x; through the first half of the
disc 3x Blu-ray is faster, through the second half of the disc 12x DVD
is faster.
And at only 4x Blu-ray manages to best a 12x DVD's maximum read speed
by 9%.
Comments
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Posted Feb 10, 2006 11:09 pm PT
If I remember my physics correctly, you're basically saying that a DVD always spins at the same rate (RPM), where blu-ray drives will spin faster when reading from the center of the disc in order to produce the same data rate. Depending on the way the disc is organized, couldn't that eventually figure into the life of the spin motor? It must be a pretty darn good one...what are the seek times that they're projecting? Now the seek time doesn't just account for moving the laser in, it's also getting to the right speed when you're there.
Thanks for the detail in your article...I'm interested to see how all of this plays out.
Thanks for the detail in your article...I'm interested to see how all of this plays out.
Posted Feb 11, 2006 6:58 am PT
The blogger is missing two key points though.
With mastered disks (game disks) data is pushed to the outer edge, not the inner edge resulting in closer to the maximum read speed for DVDs.
Second, CAV allows a lower seek time as they do not have to change the disc's speed of rotation. This is an advantage of disks with lots of files such as game disks.
With mastered disks (game disks) data is pushed to the outer edge, not the inner edge resulting in closer to the maximum read speed for DVDs.
Second, CAV allows a lower seek time as they do not have to change the disc's speed of rotation. This is an advantage of disks with lots of files such as game disks.
Posted Feb 11, 2006 8:15 am PT
The blogger is incorrect in saying that DVDs are read from the inner ring to the outer ring. DVD's can be read any way they want to be read. The rings are concentric, not spiraling. Furthermore, as a couple of you have already pointed out, DVD's can be mastered so that data that needs to be read at a high rate of speed is stored on the area of the disc with the fastest read speed. Not all game data requires maximum read speeds.
Posted Feb 11, 2006 9:08 am PT
sir....72Mbp = 9MBps |||
Posted Feb 11, 2006 9:43 am PT
The PS3's Blu-Ray drive is supposed to read DVD and/or CD media since it has backwards PS2/PS1 compatability. This suggests a drive that supports both CLV and CAV reading modes. Not only that but it's been thrown around that early PS3 games will be on DVD, though it's probably the developer's choice. I've seen mention that Blu-Ray drives will support both modes to determine the best way to read data off a disc, e.g. singular large files or multiple small files.
Posted Feb 11, 2006 1:36 pm PT
So if the PS3 will read DVDs, and sony releases DVD games, then what was this idiot's point with his bluray comparison. Basically the PS3 will dramatically slow down when bluray games come out. You know it's going to be 1x or 2x. It's a first generation bluray device for crying out loud. They're not going to make it 4x.
Posted Feb 12, 2006 11:51 am PT
Another reason to doubt the PS3s performance. Can't wait to see it in action though. So glad I didn't wait on my 360.
Posted Feb 12, 2006 2:09 pm PT
72 megabits is actually 8.78 megabytes.
Posted Feb 12, 2006 7:58 pm PT
Wa starts up most of the confusion for me:
If the Blu-ray PS3 player is supposed to be able to play DTS/THX 1080p movies , shouldn't it at least be at least 4 times as fast as normal 1 speed DVD player (The maximum bitrate for DVD playback is 10 Mbps; for HDTV (1080i)it's 19.4 to 25Mbps...for 1080p it will probably be 38.8 to 50 Mbps) the 1 speed Blu ray (36 Mbps)can barely handle that constant stream. So if PS3 is coming out with the cheapest blu-ray player in the world it will probably be 1 or 2 speed. But I think that if the one speed comes out PS3 is going to have a big problem (loading times could be 3 times as slow as the xbox360). So I think they will go for 2 speed.
The ultimate 2 speed blu-ray downside of this all is that loading times will be as much as twice as slow compared to the xbox360 loading times (which are tuned for maximum DVD read speed). but PS3 using more massive storage for their games (tuned for 1080p...yeah wright.!!.no way sony will try that..) will eventualy lead not to 2 times longer loading times but to........4 times!!!! as long!!!!!!......no way sony will do that!!!!!!!!!...so development will stick at maximum 720p maximum ...just like xbox360....
Xbox360 wins..........just because of the xbox live issue...and because they are early.....very early..
But concerning the blu-ray speed........I very hope so that SONY will come out with a minimum 2 speed player.....lesser than that is no option!!!!...just think what would happen if DTS 10.1 or some new audio standard comes out....
you could thrash youre PS3 player at that moment..because it would not be able to support it.........because the extra feed would kill the PS3 BR player
If the Blu-ray PS3 player is supposed to be able to play DTS/THX 1080p movies , shouldn't it at least be at least 4 times as fast as normal 1 speed DVD player (The maximum bitrate for DVD playback is 10 Mbps; for HDTV (1080i)it's 19.4 to 25Mbps...for 1080p it will probably be 38.8 to 50 Mbps) the 1 speed Blu ray (36 Mbps)can barely handle that constant stream. So if PS3 is coming out with the cheapest blu-ray player in the world it will probably be 1 or 2 speed. But I think that if the one speed comes out PS3 is going to have a big problem (loading times could be 3 times as slow as the xbox360). So I think they will go for 2 speed.
The ultimate 2 speed blu-ray downside of this all is that loading times will be as much as twice as slow compared to the xbox360 loading times (which are tuned for maximum DVD read speed). but PS3 using more massive storage for their games (tuned for 1080p...yeah wright.!!.no way sony will try that..) will eventualy lead not to 2 times longer loading times but to........4 times!!!! as long!!!!!!......no way sony will do that!!!!!!!!!...so development will stick at maximum 720p maximum ...just like xbox360....
Xbox360 wins..........just because of the xbox live issue...and because they are early.....very early..
But concerning the blu-ray speed........I very hope so that SONY will come out with a minimum 2 speed player.....lesser than that is no option!!!!...just think what would happen if DTS 10.1 or some new audio standard comes out....
you could thrash youre PS3 player at that moment..because it would not be able to support it.........because the extra feed would kill the PS3 BR player
Posted Feb 13, 2006 2:23 am PT
im tired of hearing all this stuff and reading it i just want to play games i love games i still play snes and gbc. i dont care how fast it goes how updated it is if it has good games i want it. xbox 360 doesnt have the games i want not right now anyways and some of the games thats been anounced for ps3 i dont think ill like so ill probably just wait to get those systems im happy with my gamecube ps2 and xbox gba and psp snes 64 ps. i hope another star wars battlefront game comes out. and if blue ray can play ps2 ps1 dvd cd and blue ray disk i think ill like it best but not until price lowers down. i sure cant wait for any of this new stuff to come out but i want good games.
Posted Feb 13, 2006 6:21 pm PT
True. But the majority of the information is only stored on the outside of the disc if the disc is full (of course the disc can be mastered with large dummy/garbage files on the inside of the disc).
I'm not sure how spinning up/down would affect the life of the motor.
You are correct, seek times are the Achilles’ heel of CLV. But where the PS3 BD-ROM will most likely be 4x or lower it won't necessarily be a factor. The speed difference between inner and outer tracks would only be ~1000RPM.
Your points are valid but were outside of the scope of my entry. This was merely a baseline comparison of read speeds.
CDs, DVDs, BDs, HD-DVDs and even Laser Discs are read from the inside to the outside (the second layer of DVD/BD/HD-DVDs is read from the outside in however).
The data track is a continuous spiral not a series of concentric circles.
I suggest you read this article.
Pay special attention to pages 2 and 6.
Noted. Thank you
Agreed. The PS3 BD-ROM will probably support both CLV and CAV. But the fact that the drive has to support 54Mbps/6.75MBps for HD video playback across the entire disc suggests that its speeds will be based on CLV.
The answer to your question is in the first 2 sentences of my entry.
There are actually two base transfer metrics for Blu-ray:
-Data: 36Mbps/4.5MBps
-HD video playback: 54Mbps/6.75MBps
The latter can handle up to 1080p.
Posted Feb 21, 2006 8:39 pm PT
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