Wednesday, October 22, 2008

Optical Drives, explained

Here is one of those hardware posts I warned you about -- but there's method to my madness (or is it madness to my method?). I bring up this subject because most commercial software comes on CD-ROM or DVD-ROM discs -- and I often distribute free-software compilations on CDs that I write myself (I write the discs, not the software). Live-Linux CDs and DVDs are another related item.

In June of 1985 I was at the Consumer Electronics Show in Chicago. Atari introduced its new Atari ST series -- but the item that most interested me was the CD-ROM drive add-on that was being shown with it. The only demonstration CD they had at that time was the first edition of Grolier's Encyclopedia. When I discovered that a CD-ROM disc could hold 640 megabytes (MB) of data, I was amazed (then-current small business/consumer-grade hard drives at the time maxed out at about 40 MB). I knew that big changes were coming at last (I had discussed the possibilities of CD and LaserDisc data storage with an engineer about 6 years earlier).

All the drives and discs I will be talking about share the same form factors (standardized size and shape) and are backward-compatible with earlier types; this means that a Blu-Ray burner will read (and write) CDs and DVDs as well. With the right software, media discs (audio and movies) can be played on the attached PC. There are different drive form factors for desktop and laptop PCs; within each class the drives are usually interchangeable. Due to physical (size) limitations, laptop drives read and write discs at a somewhat slower rate than desktop drives. For this reason, and to reduce wear-and-tear on the internal drive, I often use an external USB-connected drive with a laptop.

Each generation of discs and drives has held more data than the previous generation. CD capacity is 640 MB to 700 MB (depending on discs). DVD capacity is 4.7 gigabytes (GB) for a single-layer disc, 8.5 GB for a dual-layer disc. Blu-ray discs hold 25 GB on a single-layer disc, 50 GB on a dual-layer disc. There are indications that a next-generation Blu-ray disc may hold as much as 200 GB on a single CD-sized platter.

Typical 50-100 quantity prices for writable media range from about 15 cents for a blank CD-R, to 25-50 cents for a single-layer blank DVD, $1.50-$2 for a dual-layer blank DVD, up to $8-$15 for a single-layer Blu-Ray BD-R disc, and $25-$30 for a dual-layer BD-R disc (1-25 quantity). I expect the BD-R media prices will come down over time when the volume ramps up -- when I first got my CD burner, 4x blanks were about $1.50 each. There may be more about the optical media itself in a future installment.

The first iteration was the CD-ROM drive. Starting out at a read-rate of 1x (the same speed as an audio CD, about 150 kilobits-per-second), speeds soon ramped up. Microsoft's MS-DOS soon had an add-on that allowed DOS to read the CD file system, as did most other computer operating systems at the time. Current desktop optical ROM drives read (transfer data from) CDs at a 48x-52x rate -- but very few (if any) CD-ROM-only drives are currently being manufactured.
: CDs (older drives -- those manufactured prior to 1998 -- will probably not be able to read CD-R or CD-RW discs).

Next was the DVD-ROM drive, introduced in 1997. Starting out at a read-rate of 1x (the same speed as a DVD movie, which is about 4x faster than a 1x audio CD) it, too, quickly ramped up in speed. Current optical ROM drives read DVDs at a 16x-20x rate.
Compatibility: CDs & DVDs (older drives manufactured prior to 1998 may not be able to read writable media: CD-R, CD-RW, DVD-R/RW, or DVD+R/RW discs). A new DVD-ROM drive will set you back about $20-25.

At about the same time as the DVD-ROM was introduced came the CD "burner" (writer) drive. As CD write speeds ramped up above about 8X, a problem became evident -- the computer could not always transfer data to the drive consistently and the data interruption (known as buffer underrun) led to write failures. Sanyo developed what is now referred to as buffer underrun protection (sometimes called BURN-proof) -- all current writable drives (and the software for them) keep track of where they are on the disc during the write process and can pick up where they left off if the buffer (internal temporary storage memory) empties during a write cycle. Current optical ROM drives write (transfer data to) CDs at up to a 48x-52x rate.
Compatibility: read/write all CDs. A new CD-writer drive will cost about $20 -- I paid nearly $300 for my first 4x CD writer in 1999. Note: all older drives will require a
firmware update to write some current discs.

It was not long before a DVD-ROM drive was combined with a CD writer to make what is now called a combo drive, with all the features of both. These have mostly been superseded by full-featured DVD writers.
: read/write all CDs and read all DVDs. Note: all older drives will require a firmware update to write some current discs.

Next came the DVD burner. First-generation drives wrote DVD+R/RW and CD-R/RW only; DVD-R/RW drives and discs soon followed from a different industry consortium and could burn CDs as well. In general, the + and - drives could read (but not write) each others' discs. Current DVD writers are +/- write-compatible, but check the front-panel markings on a particular drive to ensure it will write the discs you feed it. Current desktop DVD-writer drives write single-layer discs at 16x-20x; Current laptop DVD-writer drives write single-layer discs at 6x-8x. Dual-layer discs are written at 4-8x depending on the type of drive and the media used.
Compatibility: read/write all CDs and read all DVDs. DVD write-compatibility varies with the drive; newer drives (since about 2004) write all types. Note: all older drives will require a firmware update to write some current discs.

The newest optical-disc formats are HD-DVD and Blu-ray, though the HD-DVD format has already fallen by the wayside (much to the chagrin of Microsoft). There are Blu-ray combo drives that add Blu-ray ROM and movie-reading capabilities to a DVD-burner drive.

The pinnacle of the optical-drive heap is the Blu-ray writer drive. Current Blu-ray writers can write BD-R media at up to 8x, which is a whopping 288 megabits (Mb) per second -- a nearly 2000 times faster data-transfer rate than a 1x CD at 150 kilobits (kb) per second.Compatibility: read/write all CDs, DVDs, and Blu-ray media.


Jonbo said...

Interesting piece about the ST. That was the era that I came into my own.

Of course ST lost the battle to the far superior A500, which I was heavily involved with (demo scene)

Atari havent had much luck recently, what with the scandal surrounding its Alone in the Dark release and the fact that IMO the company has offered nothing since the release of the ST that makes them stand out. (and as I say Commodore managed to get the better of that platform anyway)

I believe Atari will be a victim of this credit crisis. I predict by this time next year.

"The Linux Blogazine"

Charles said...

Michael, some CD-R's appear to have a capacity of 800MB... I first came across this when I went to burn a particular gOS disc that was over 700MB.

Great article!