Hi-MD read/write speeds vs. data transfer speeds

[dex Otaku]

People have been repeatedly emphasising how slow MO media are since I started reading here.

Sony's choice of using USB 1.1 is a mystery to me, but I don't think it has anything to do with how quickly the discs can read or write.

See http://minidisc.org/hi-md_faq.html#r_q104

Perhaps the real issue is Sony's DRM? Encrypting/decrypting and transcoding? I don't know. I have no experience with Sonicstage yet.

All I know is that the stated specs don't reflect the opinion that the speed of the medium is severely bottlenecking even USB 1.1. [Funny note: Sony's product literature on the web mostly say that Hi-MD uses USB 2.0]

Thinking.. Stated data rate is 9.83Mbps .. USB 1.1's is 12Mbps .. standard PCM is 1.4Mbps .. so even writing PCM back to the disc should be possible at faster than realtime speeds.

Of course, write speed and read speed need not be the same, but write speed must be at least the 1.4Mbps for PCM to work.. which would not be fast enough for claimed "100x" transfers of even 48kbps content.

Still seems like a software issue, to me.

[Ppk3000]

I think it's the physical process of writing/reading from the magnetic disc... I've read about magnetic backup as a solution for large storage servers and one of the main issues is slow transfer speed.

However, it is possible that there is an artificial limit somewhere. Maybe Sony has capped the speed at 100x so they can easily achieve and advertise greater speed for future recorders... never know... :whatever:

[Qwakrz]

DRM can be proved to not play a part in the slow transfer as it also affects data that is placed onto the new discs.

Also a little bit further down is the physical specs for the disc's including a theoretical maximum read speed of 9.83Mbps but this does include all error correction etc and refers the the bits actually being transfered from the disc. I would presume it is read speed as it falls into line with the read tests reported on minidisc.org's site. Write speed will however be lower.

[highlandsun]

What is the actual question you're asking?

It's clear that USB1.1 at 12Mbps already exceeds the 9.8Mbps that the medium is capable of, so there's nothing to be gained by using any faster interface, like USB2.0.

If you're asking where Sony gets their "100X" claims from, obviously it's pure marketing BS because actual transfer speeds in real life are always slower.

As for software-limited speeds... Let's see, doing the math at 48kbps I guess you would expect to be able to transfer at 200x, is that the point? Of course, this assumes 100% efficient use of the USB bus, which will never happen, because USB is inherently inefficient. There are turnaround delays for commands and data to go back and forth from the PC to the device. And even in "bulk streaming mode" you can't stream more than XX Kbytes without waiting for an ACK (I think the limit is 64K, it is most likely smaller on most portable devices.) At 48kbps, 100X represents 50% efficiency, which isn't great, but isn't surprising either given how lousy the USB1.1 design is.