Copyright © Daniel Rutter 1996. All rights reserved.
650 megabytes of storage for under $20. Sure, you can only write to it once, but for the money, who cares? But theres a lot more to CD writers than meets the eye.
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Burning CD-ROMs isnt just for rich folk any more. With double speed writers available for street prices around $1500, CD-R is becoming a permanent storage solution for the masses. The quality of the support software has also improved, with the cheap writers coming with friendly software that lets you make plain audio or data CDs, and plenty of other mastering packages that support several popular drives and will satisfy the vast bulk of users.
There are still shortcomings. No matter what the salesman tells you, writing CDs is not nearly as straightforward as writing to ordinary rewritable media. While you no longer need a degree from the Propellorhead Institute to work the software, its still a long way from being perfectly intuitive.
CD writer software, especially bundled packages, can also be well short of a comprehensive feature set. If you want to make Video CDs, CD-I discs or multiplatform discs (data discs compatible with two or more operating systems), most CD mastering software will be no use to you. The ability to write simultaneously to multiple CD burners is also rare. Fortunately, relatively few users need these features.
A perfectly good CD writer can be made to look lousy by bad software. If the softwares design makes corralling the files you want awkward, it can take longer to make a CD with a quad speed writer than a double speed writer with better software. Likewise, if the softwares not optimally compatible with the particular CD writer its paired with and so doesnt use the writers full speed, or its transfer rate calculations are inefficient or (worse) overly optimistic, your CD writing experience will not be a happy one.
We checked out three competitors in the cutting-edge quad speed CD writer department, from Yamaha, Sony and Pioneer. Two are very good. One is not. Read on.
Yamahas CDR 100II mechanism can be found in more than a few bundles, and is supported by a wide range of mastering packages. Its a quad speed reader and writer, which can also read and write at single or double speed.
Yamahas own external version of the CDR 100II is the CDE 100II. Theres also a CDR 102 mechanism out there, which is a double speed only version. Do not think the higher serial number indicates a better drive.
The Yamahas chief competition is the Sony Spressa 940. The Sony has speed specs better than the Yamaha and comes bundled with Corel CD Creator II, the only CD mastering package that manages to be simple for beginners to use and, simultaneously, capable of efficiently handling all popular formats. The Sony is also capable of incremental packet writing, still a rarity in drives at any price. The Sony software lets you easily copy files to CD-R as if it were an ordinary random-access device, without huge areas being taken up before and after each write operation. Discs so made can only be read if youre running the right drivers - you cant just hand them out hither and yon - but CD Creator lets you write old-style discs as well.
Up against these two is the Pioneer DW-S114X, but its not much of a competition.
The Pioneer looks, at first glance, like a 6 disc stacker. Its a monster. The external Yamaha CDE 100II is 170 by 65 by 320 and weighs 3.1kg; the internal Sony we checked out is normal half height 5.25" device sized, but the Pioneer external is 210 by 115 by 399mm and tips the sales at 5.3kg. Mind you, youd want some size and mass for your money; the Pioneer drive is more than twice the Yamahas price.
The Pioneer behemoth has few advantages over the much cheaper Yamaha and Sony. It has a 1Mb data buffer, like the Sony; the Yamaha has only 512k but does OK with it. The Pioneer has a simple tray load system; both the Yamaha and the Sony use irritating caddies. And the Pioneers bundled software, Incats Easy-CD Pro for Windows 95/NT and Mac, is OK but not up to CD Creator standards. The Yamaha has no bundled software by default, but is available in various packages.
And thats as good as the news gets for the Pioneer. With a 630 millisecond 1/3rd stroke access time, the Pioneers performance as a reader is sluggish. The Yamahas no speed demon (500ms), but it is faster, and the Sonys quite useable as a reader with 250ms average seek. You also cant actually use the Pioneer as a reader under Windows 95 or NT unless you use old 16 bit drivers. It shows up as a CD-ROM drive, but its permanently "not ready" without the antique drivers; not so with the Yamaha or Sony.
The Pioneer has no analogue audio outputs - no RCA jacks, no headphone socket. The Yamaha has RCA sockets only, the Sony internal has the standard audio jack that plugs into a sound card. The Pioneer can of course send audio data over the SCSI interface, but youll need a separate player to check your written audio tracks.
This audio incapability is no doubt connected to the Pioneers inability to operate at single speed (150k/s). It can write at double speed, which should take care of any slow-computer problems, but the Yamaha and Sony can happily do everything at single, double and quad speeds. The Pioneer is also incapable of Disc-at-Once recording, making it a lot less useful for production of discs for replication; the other two have no problem with it.
If a dimensional rift swallowed the Yamaha and Sony drives, the Pioneer might enjoy considerable popularity. But when a drive that wins on all important features is available for half the price, the Pioneer giant starts to look disturbingly dinosaur-ish. Of the remaining two, the Yamahas the universally accepted bargain buy, and the Sonys got more features and good standard software.
HP SureStore 4020i
Hewlett-Packards 4020i is aimed at the low end CD writer market, giving you an internal double speed writer, controller card, software and eight blank CDs (a 10 disc offer is current at the time of writing) for under $1700 list price. Installations simple enough provided you remember to install the card before trying to set up the software; the card isnt Plug And Play, but proper Windows 95 drivers are included so setup is no big deal.
Physically, the SureStores a decent gadget. Based on the Philips CDD2000 mechanism, it has a tray for CDs (not a caddy system), a hefty 1Mb of buffer RAM, double speed writing and quad speed reading,
The 4020i originally got bad press, because it was pushed to market and came out in the States more than a year ago with buggy firmware and beta software. Those problems are now behind it. Do not believe old reviews of the drive. Now it works.
The SureStore comes with a cutdown version of Easy CD Pro called Easy CD for HP. Its divided into separate modules for the different functions and does basic tasks simply enough. You also get Alchemy Personal and Magic Lantern for Photo CD
If youre after multi-format support, the SureStores included software is not much good. You can write ordinary data, audio and XA discs, but you cant mix audio and data on one disc, you cant write Photo CDs (Magic Lantern is a viewer package), and you cant make Mac format discs. If you use other software - anything that supports the SureStore, or even the Philips drive its based on - the writer has no trouble with all the other common formats.
Alchemy Personal is a cutdown version of the full Alchemy 2.0, but its still a handy system for creating databases of documents and spreadsheets on CD, with comprehensive searchable indexing.
Blaster CD-R 4210
Creatives Blaster CD-R 4210 is obviously and unashamedly aimed at the home market. In the box you get a SCSI card, a double speed writer/quad speed reader based on the Panasonic CW-750C mechanism, and friendly software and documentation.
Installation is a doddle, with the standard mechanism showing up as a perfectly functional CD reader under Windows 95 without any driver twiddling, and the software installation just as simple. The software, the full version of Easy-CD Pro, has that distinctive gussied-up look that packages built for the masses tend to exhibit. But it works OK; theres a simple drag and drop interface for building data discs, and the audio CD compilation program lets you print jewel case liners, with lots of attractive templates included. If youre looking for unusual formats and speedy operation this software wont fit the bill, but it does the job for the home user.
In performance, theres nothing very special about the CD-R 4210. Reading from audio discs is slow and painful, as the drive is incapable of reading audio faster than single speed, but thats the only significant bad point. The Panasonic mechanism has a 1Mb data buffer, which coupled with its 2X top speed makes it quite tricky to make a coaster. This is a cheap package, its easy to use and it carries a big brand name, which doesnt hurt.
The Philips CDD2000 is one of the cheapest double speed CD writers you can get; it lists at just over $1000 for the bare drive, putting it well under the price of other double speed bundles even after you add decent mastering software and a SCSI card (if necessary). For your money you get a mechanism with the usual double speed write/quad speed read specs, but also compatibility with all CD types, Disc-at-Once, and even incremental packet writing. And its a tray-load drive - no caddies.
The CDD2000 is a thoroughly adequate drive with all the features, and its available in a number of packages under different branding - the HP SureStore 4020i uses it, for instance. These one box solutions are unlikely to offer much of a price advantage over more recent offerings like Creatives Blaster CD-R; if you roll your own package with a CDD2000, card and software, youre likely to be able to get into CD mastering with enough spare cash for 10 or 20 more discs.
The Optima Diskovery 650 CD-R brings easy, non-technical CD mastering to Macintosh users. Any CD burner can be used on the Macintosh with appropriate software, but this is a one-stop solution that doesnt break the bank.
For your $2245 you get a double speed caddy load writer (quad speed read), two blank discs and the Toast Pro 3.0 CD-R Access and Quicktopix software packages.
Macintoshes, generally speaking, are easy to use. Persons used to recent PCs, however, may be somewhat startled at what you have to do to get CD mastering working on a Mac. You need at least 5Mb, possibly up to 8Mb, of contiguous free space on your startup drive. If yours is a well-worked Mac youll have to optimise the drive, and because of the Macintoshs fascistic insistence that Files In Use Must Not Be Moved, youll have to boot from another hard drive or removable cartridge in order to run an optimiser such as Speed Disk from Norton Utilities.
To install new extensions you have to boot your Mac without its current extensions running, so start up on your freshly optimised drive with the shift key held down.
If youre using the Apple Audio CD Driver, Vulcan Soft Partition or a couple of other extensions, theyll clash with the WarpVelo and CD-R extensions installed by the package. Youll have to turn them off in the extensions manager, or your system will hang on startup. Moreover, unfortunately, the latest release of CD-ROM Toolkit does not recognise this new product.
The Optima software lets you mount the CD-R on your desktop and drag and drop files to it. The software transparently patches the discs table of contents so it only has to be updated when you eject the disc. This may be convenient, but since only slightly modified CD mastering goes on whenever you write to the disc, 22Mb of lead-in and lead-out space is wasted the first time you write to the disc and 13.5Mb every other time you do a write. It is thus possible to fill an entire 650Mb disc with fewer than 50 1k text files. Its also possible to delete files, but you dont back the space they took up. If you avoid using CDs as if they were ordinary media, though, the software is very good. You can write all popular formats (not just HFS) with the exception of Photo CD, and the 1Mb buffer means buffer underruns are rare. Theres a specific Track Recovery feature for dealing with aborted tracks.
The CD-R Access Control Panel allows the user to view SCSI devices attached to the Mac, view the status of a connected drive, view disk information and work on disk directories. Theres configuration options for finalising, error reporting and directory size. Discs or disc directories can also be repaired directly from the control panel window. It is also possible to write protect a CD-R until youre ready to add more data to it. Fully integrated balloon help is another helpful feature of the software, allowing experts and novices alike to optimise performance.
The Optima Discovery is a well worked out bundle thats no more annoying to set up than any other Mac CD writer. The drive is good, the softwares fine, and the price is not overly inflated.
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Burning by Amiga
The Amiga has one, and exactly one, CD mastering package. Its MasterISO, its current version is 1.23, and it used to cost a fortune but is now down to $US199. MasterISO supports the Yamaha CDR-100 and CDR-102, the Sony CDU-920, Pinnacle Micros RCD-1000, RCD-202 and RCD-5040, Philips CDD-522, CDD-521 and CDD2000, the Pioneer DW-S114X and the HP 4020. It can only create standard audio and data CDs.
MasterISO comes from AsimWare, the makers of the excellent AsimCDFS. This CD filesystem turns any CD-ROM equipped Amiga into a remarkably compatible data extraction machine - very easy access to Photo CD and read compatibility with all ISO-9660 formats and HFS too. It doesnt make the Amiga capable of doing anything with the PC and Mac executables and data it can read, but its a good stepping stone.
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CD Writing Decoded
There are two basic ways to write a CD - directly, and via an image file.
Direct writing, also called a virtual image file, is the more advanced way. Its more stressful to the computer but less stressful to you, because it lets you just assemble the directory structure you want to write to the CD and then send it off. From your point of view, it looks as if the softwares just copying all of the files onto a not very fast 650Mb-odd hard drive, but the CD mastering softwares actually doing some rather clever gymnastics to make sure the right piece of data is fed to the drive at the right time. This is because CD writers are not random access when theyre writing a CD - they have to write from the beginning to the end with no breaks, and cant be interrupted. If you interrupt the write, you have, in technical parlance, made a coaster. That $20 blank CD is now suitable only for putting under a drink.
It is eminently possible, especially with faster CD writers, for direct writing to go awry. Buffer memory on the computer and in the writer holds data destined for the disc, and prevents brief interruptions and hard drive seeking from interrupting the write operation. But if your computer fails to keep up with the write rate for long enough for the buffer to empty, you get the dreaded "buffer underrun", and youve made a coaster. Youll probably be able to close that aborted session and still use the remaining space on the disc minus the 13.5Mb session overhead, but thats little consolation.
Buffer underruns are surprisingly common until a CD writers correctly set up; the faster the CD writer and the slower the computer, the more of a problem they are. The worst case scenario is if youre writing lots of small files from a fragmented hard drive, but even systems that would seem to have tons of spare speed can fail to perform a write correctly if a background OS function flogs the drive half way through the lengthy write operation, or the hard drive does a thermal recalibration. These sorts of semi-random hiccups can mean that a borderline machine writing the exact same data can do a perfect job two times out of three but create a coaster the other time.
The simplest way to overcome buffer underruns is to set the CD writer to a lower speed - many writers can be set back to the languorous single speed 150k per second rate, and while this means writing a disc can take more than an hour, its unlikely youll have an error. If youve got more hard disk space, though, an image file, preferably on a different physical drive (not partition) from the main system drive, could be the way to go.
Image files used to be the only way to write a CD. The technical name for the data format on all standard CD-ROMs is ISO-9660, and a CD image file is just the byte-for-byte identical data for a CD, stored as one humungous ISO-9660 file on a hard drive instead. The mastering software constructs the image file on the hard drive, doing as much seeking and thrashing as it needs to; you can then write the file to the CD, without having to seek to all of the individual files. If you do a quick free-space optimisation of your hard drive before you build the file and dont do any multitasking during the write, its considerably harder to make a dud disc this way. Some mastering software also lets you use the ISO 9660 file as a pseudo-CD, so you can see if everythings working and find any filename conversion problems. But you will need up to 650Mb of free hard disk space. Some software may let you browse through a virtual image file in the same way, but its all just smoke and mirrors - the final disc may still have problems, and no matter how realistic the software makes it look, a virtual file does not have the write-time advantages of a good old fashioned physical image file.
If youre using Corel CD Creator 2, you can create partial image files. Partial image files image on your hard drive only those files stored on slower devices, like other CDs or unreliable network drives. Partial images can be a handy compromise.
If youve got a spare hour, set your writer to single speed and you shouldnt have a problem. Recent Macs and PCs should also have little trouble with double speed writers, especially those with 1Mb of buffer RAM against the older 512k models. Quad speed writers, however, can present a challenge. Remember, your computers almost definitely able to deliver an average of 600 kilobytes per second. But the surges and droughts in this data stream have to be small enough for the buffer to handle. If theyre not - coaster.
There are platform-specific issues to consider when writing CDs. Macintoshes have slow I/O, so even fast PowerMac systems may have to use a physical image file to write to faster CD burners. IBM compatibles with namby-pamby tree-hugging power saving features should have them disabled from the BIOS setup screen so you KNOW theyre off. Likewise, suspend your screen savers and scheduled programs. If a machines been chugging away on a CD write for 20 minutes and the screen saver cuts in, or an untouched hard drive spins down, or a scheduled disk defrag operation commences you get the picture. Windows 95 users should also disable Auto Insert Notification, as it coexists poorly with blank CDs.
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CD-R Question and Answer
Whats the difference between CD-Rs and regular CDs?
Regular CDs are stamped out in a factory with an aluminium or gold reflective layer; CD-Rs have an organic dye on the reflective layer which can be written to once by a CD writer. After writing, CD-Rs behave very much the same as ordinary CDs; theyre not as tolerant of high temperatures, direct sunlight or humidity, but generally speaking need little more care than regular CDs. A few CD-ROM drives may have trouble reading CD-Rs, and cheap CD-Rs can exacerbate the problem, but compatibility problems are very much the exception rather than the rule.
Why are CD-Rs different colours?
Standard CDs are either silver or gold, indicating a reflective layer made of aluminium or gold. Recordable CDs are come in green, gold or the uncommon blue, indicating the colour of the dye layer that the writing laser burns holes through to encode data. Green discs are the oldest technology, and deal better with read/write power variations, which makes them slightly more compatible overall. Gold came next; it lasts longer than green (100 year quoted lifespan against 75) and may be more reliable for high speed recording. Blue, which is the old green dye with a silver alloy substrate, is the coming thing and billed as giving lower errors and better UV stability. Incompatibility problems are rare but can be bizarre. Some audio and data drives, especially older models, dont work with one or more types of disc. Some are even finicky about the brand, the speed at which the disc was recorded, or the writer that recorded it.
What capacities are available?
CD-Rs come in 80mm and 120mm sizes, though the 80mm size is as unpopular as 80mm CD singles. There are two capacities available in 120mm - 553Mb (63 minutes of audio) and 650Mb (74 minutes). 80mm CD-Rs are 184Mb (21 minute). A full 74 minute audio disc actually contains 740Mb of audio data; the data capacity is only 650Mb because only 2048 bytes in each 2352 byte sector is used for data, the rest being error correction and other information.
How long does burning a CD-R take?
All CD writers are not alike, even if they claim to be the same basic speed (single, double or quad). The variations in writing speed between different units of the same basic spec, however, are unlikely to make a lot of difference. If youre filling a disc (650Mb of data) it will take about 74, 37 and 19 minutes respectively at the three currently available base speeds. Half the data will take half the time. Theres also one or two minutes on the end for finalising the write operation.
Why are audio CD recorders so expensive?
Audio CD recorders use low speed CD-R mechanisms in a hi-fi component cabinet. They need special more expensive blanks that only hold 60 minutes of audio, and they may use the Serial Copy Management System (SCMS) to make it impossible to copy copies. All the crippling is thanks to the same legislation frenzy that killed DAT as a home recording medium, and the higher price is partly due to lower sales volume and partly because every blank you buy has part of its price donated as a royalty to a studio consortium, on the assumption that youre going to pirate copyright material.
A good audio digitising card (not a plain sound card) and even a cheap CD-R drive will let you do exactly the same job on your computer. If you already have a computer, buying an audio CD recorder marks you as something of a goose.
What about CD-Rewritable?
The current writable CD standard is CD-Recordable, in which you can only write once to a disc and any "deletions" just cordon off a disc section - you dont get the space back. CD-Rewritable, also known as CD-Erasable or CD-E, will be available at hefty prices towards the end of this year, and will allow true deletion with space reclamation by using a phase-change technology akin to that of Panasonics PD Drive. CD-E is compatible with standard CD readers like CD-R, but cannot be written by current CD writers.
Are internal CD recorders better than external?
Cheaper - yes. More reliable - not necessarily. CD writers dont like to get hot - they cant tolerate the same temperatures hard drives and CD readers can. You wont damage the writer if it overheats, but the rate of failed writes and useless discs may rise. If your computers case is well ventilated, an internal drive should work just fine. Modern machines with two fans should be OK. But external drives are built with sufficient ventilation to start with.
Whats a bus mastering controller?
The salesman says you need a bus mastering SCSI controller for reliable CD writing. Guess what? Hes right. A bus mastering controller can bypass the CPU when accessing memory. It doesnt have to wait in line with everything else, and is hence less prone to interruptions. There are plenty of bus mastering controllers available; if youre using a PC with an elderly SCSI controller, it probably isnt. Dont think the old controller will be up to scratch because it only needs to deliver, say, 300k per second to your double speed writer. That way lies coasters.
What the heck are all these subcode channels?
Answer 1: Something you almost definitely dont need to know about.
Answer 2: Compact discs can have extra data "hidden" on the disc in up to eight subcode channels, melodiously designated P, Q, R, S, T, U, V and W. Each channel can hold up to about 4Mb of data, and that data is distributed across the whole disc.
The Q channel is the only commonly used one. Its automatically written and contains position information (used by audio CD players). It can also be used to store the International Standard Recording Code (ISRC) designator which indicates the country of origin, owner, year of issue and serial number of each track, and the media catalog number, a similar designator for the whole disc. Usually, it just stores the position information.
Whats write testing all about?
Before burning a CD, especially if youve changed something in the system or just installed your CD writer, its a good idea to make sure your computer is capable of writing a disc at the currently selected speed. If your system cant consistently deliver data fast enough and the write buffer empties, youve wasted a CD-R.
The best way to make sure the systems fast enough is via a write emulation test, where the system goes through the motions of writing a CD, including passing data to the CD burner, but doesnt actually turn on the burners laser. If you pass this "dummy write" test and nothing changes for the real write, your disc will be correctly written.
A less useful test is the basic speed test, where your system tests how fast it can collect all of the files destined for the disc and copies them to nowhere. The dumbest version of this just divides the total data transferred by the time taken and takes that average figure as the transfer rate; this doesnt take into account inconsistencies in data delivery and can be close to useless. A better version correctly monitors transfer rate throughout the speed test; it still doesnt take into account possible system slowdown from actually moving the data to the writer.
I did a test write, and when it finished my CD writer ejected its caddy. What gives?
In between a test write and a real write, many CD recorders have to clear their memory. A simple "clear memory" command would do the trick, but frequently CD recorders have no such command. Ejecting the disc clears the memory, though, so thats what the recorder does. If your CD writer has a tray it will slide it out and back in, which may surprise you but is not especially annoying. If its a caddy drive, youll have to push the caddy back in by hand. A marvellous design feature, Im sure youll agree.
Whats Running OPC?
Running OPC (Optimum Power Calibration) is a system used by the CD writer mechanisms in HPs SureStore 4020i and the Sony Spressa, among others. It keeps an eye on the pits being cut in a CD-R blank and adjusts laser power to compensate for disc quality, dust, fingerprints and so on. This system may improve the reliability of the written data, and it also allows the writer to tell when it could be making a dud disc and alert the user to check the data at the end of the write.
Whats so bad about caddies?
There are two ways to load a single disc CD-ROM drive or CD writer - tray and caddy. Trays work just like the tray on an audio CD player. Caddies are flip-top cartridges into which you pop your disc. The caddy has a sliding metal door that only opens when its in the drive, and so the CD is kept safe from scratches and dirt.
Unfortunately, nobody ever seems to have as many caddies as discs, and youre more likely to scratch a disc when fumbling it into a caddy than when dropping it into a tray. The real differences in disc safety are small - it doesnt take much care either way to keep your CDs safe - but caddies are awkward and annoying. Tray load designs are more expensive to build and can be spectacularly broken if you lean on the open tray (so, to quote Groucho, dont do that), but theyre the better option.
Whats the difference between a buffer and a cache?
The words buffer and cache are often used interchangeably; they both describe RAM used to temporarily store data, but theyre not the same. A buffer, though, is memory used to store data being moved from one place to another, to compensate for speed differences between the read and write ends and soak up any interruptions. A cache is used for temporary storage of data which is not being moved anywhere, but to which the system needs very quick access. In the case of CD mastering systems, the drive will have its own 512k or 1Mb buffer, with another configurable buffer assigned at the computer end. A buffer can act as a cache - it holds the data last read, and if the same datas requested again it will deliver it without actually accessing the drive.
Uh, what exactly IS a thermal recalibration?
Youre burning a CD. Your hard drive hiccups for no obvious reason, and you make a coaster. It might have been thermal recalibration (tcal).
Tcal is what a hard drive does to compensate for increased platter temperature, caused by air friction inside the drive. Hotter platters expand, and the drive has to keep its heads properly lined up with its servo tracks, so it pauses for about 40 milliseconds per platter - 0.2 to 1 second, for most drives. In that time, the write buffer drains and your CD is hors de combat.
The latest hard drives using embedded servo tracks (older drives have one whole platter surface dedicated to the head-locating servo data) and magnetoresistive (MR) read heads do not need to do tcals. But everything else, be it a fancy pink-framed AV drive or one of its less pretentious (and mechanically identical) siblings, does. AV drives, and other high performance SCSI drives, do tcals when no data is being requested, and can interrupt them when a data request comes in. They take advantage of the fact that when a tcal is necessary, data can still be read - the error rate is just higher than normal. But a three millisecond re-read delay is OK. A one second tcal is not.
Many recent drives can be tweaked to change the tcal mode, and to further enhance performance by doing things like disabling data write verification. There may be a jumper to do it, or you may need a little utility, probably available from the manufacturers. For CD mastering, switching to interruptible tcal should be enough to avoid those mystifying moments when the hard drive suddenly decides not to play ball.
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Theres more than one way to write a CD, and the differences can be important. Not all mastering software and not all drives support all modes.
The differences all centre around the fact that CD writers do not operate like ordinary random access media when theyre writing. They "stream" data onto the disc, just feeding the data flow from the computer onto the disc surface. They dont have to write a whole disc in one go, but they generally have to write at least one track. There can be up to 99 tracks on a disc, of at least 300 blocks in size (about four seconds of audio or 700k of data). Ordinary data CD-ROMs only need one track (although they can have more), and thats all you could write to a CD-R before the advent of multisession.
Multisession is writing to a CD-R at different times. The time between writes can be a second or a year; the CD writer finishes up the session, writes a chunk of extra data to indicate the start point for future writes, and can then safely stop without corrupting the disc. Every CD-ROM drive and CD writer sold today supports multisession.
In the olden days, though, the only write mode on CD writers was single-session recording, also known as track-at-once. Track-at-once lets you write one and only one track, in one and only one session, to a CD. If you were only storing 200Mb of data, the rest of the space was wasted.
Single session has now been succeeded by Track Multi-session, with which you can write in multiple sessions. If the drive allows it, each session can comprise one or more tracks, up to the disc maximum of 99 tracks. This is useful for compiling audio discs; tracks are automatically separated with 2 seconds of pre-gap.
Track Multi-session, though, is far from optimal - it wastes about 13.5Mb of disk space every session for "lead-in" and "lead-out" areas. It can also produce discs which are unsuitable for commercial duplication. This is because the lead-in and lead-out areas arent physically located perfectly before and after the data track/s written - the lead-in area cant be written first, because the drive doesnt know how much data its going to be sent, and the lead-out area is written after the drives received the end-of-data message from the computer and turned its laser off. This means each session comprises three separate write operations, with the laser turned off in between and "link blocks" written to indicate where the lead-in and lead-out information actually is.
Most disc mastering systems, however, dont recognise link blocks and wont duplicate these discs. To eliminate this possible incompatibility and the wasted space, you have to use Disc-at-Once mode.
Disc-at-Once writes an entire disc from beginning to end in one go, and doesnt allow multiple sessions. The mastering software has to tell the CD writer what its going to send so it can get the (smaller) lead-in and Table Of Contents (TOC) area right. Disc-at-Once is not supported by all CD writers, but most presently available mechanisms can do it.
The next stage in writing to CDs is incremental or packet writing, a further loosening of the rules. Incremental writing uses an extension of the current ISO9660 file system called ECMA 168, and it makes it possible for data to be written to discs in small increments without huge lead-in and lead-out areas and without having to rebuild the whole file system every time. Incremental packet writing makes CD writers behave a lot more like conventional hard drives, albeit without he ability to delete data and get the space back. Packet written discs are not legible by other drives unless youre running a special driver to deal with the new file system, and ECMA 168 hasnt been finalised yet so incompatibility problems are likely. Some drive mechanisms support packet writing already - current Sony mechanisms and the Philips CDD2000, for example - but this fact is of only academic interest if your operating system doesnt have CD-R packet writing drivers. An imminent Windows 95 upgrade will provide said drivers to all Win 95 users, and Sony package drivers with their compatible drives.
Different writing modes can be particularly important when youre creating audio discs. When recording audio CDs, you may get clicks in between tracks. There are two possible causes of inter-track clicks - lousy software, which is writing computer file headers or footers along with the audio data, and track-at-once recording, which writes run-in and run-out sectors on either side of each track. Disc-at-once recording avoids this problem. You should be writing audio CDs in only one session anyway, as few audio CD players can play anything beyond the first session.
If you still get clicks, or you get clicks at places other than the beginnings and ends of tracks, then the culprit is the read process, the write process, or both. Different CD reading mechanisms extract slightly different bit streams from audio CDs (which, by the way, is the source of the scads of audiophile CD transport/DA converter tweaks out there), and if your CD mechanism can read audio data at faster than the standard single speed rate, itll probably get more errors then. The same applies to the write process; if the copy of the audio data on your hard drive sounds fine but the final disc doesnt, the write process is at fault and you should drop to a lower write speed and/or try higher quality media. Audio data errors have to be pretty drastic before theyre audible, though (golden eared hi-fi purists may direct comments on this statement to this magazine).
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There are a plethora of formats for compact discs, many of which are named for the colour of the book defining them. Heres the quick rundown.
Red Book - Audio CD, also known as Compact Disc Digital Audio or CD-DA. Launched in October 1982.
Yellow Book - The original Data CD format. Yellow Book does not allow mixed data and audio tracks.
Green Book - Philips unpopular CD-I format. Proprietary; not ISO-9660 compatible.
Orange Book - The physical format for recordable CDs. Has the subsections Part I, for CD-MO (Magneto-Optical), and Part II, for CD-WO (Write-Once), which is CD-R as we know it. Orange Book is most significant because it introduced the multisession concept, in which data can be added in separate sessions and the discs TOC (Table Of Contents) maintained appropriately.
White Book - Format for Video CD.
Blue Book - CD Extra, Enhanced CD or CD Plus, a format for discs which play as normal audio CDs but also contain CD-ROM data, with the Red Book and Yellow Book sections recorded as separate sessions. Blue Book is also occasionally, and incorrectly, used to mean analogue laserdisc format; Pioneer apparently has a pre-mastering guide that might have had a blue cover in some edition, but its not the LaserDisc standard reference and, in case you missed it, 12" laserdiscs are not 120mm CDs.
CD-ROM XA - eXtended Architecture, the current standard for multimedia discs which allows data and audio to be interleaved. CD-ROM XA stores data differently from plain old Yellow Book data discs; XA data should not be mixed with ordinary Yellow Book data on the one disc, or coasters will result.
ISO-9660 - Standard file layout for CD-ROMs. Originally called High Sierra. ISO-9660 only supports MS-DOS style eight character filenames with three character extensions, with many non-alphabetic characters forbidden. Theres a further file version number, separated from the name with a semicolon, but many systems ignore it - Macintoshes with a version of the ISO 9660 File Access extension below 5.0 may have problems with version numbers. Plain ISO-9660 directories can only be nested eight levels deep.
Level 2 ISO-9660 is an unpopular format which allows longer filenames and 32 levels of directory nesting, but doesnt work with MS-DOS systems.
Rock Ridge - ISO-9660 extension, which permits long file names and other enhancements. Systems which dont support long names see them as truncated, but can still access the files. Well, thats the theory; Rock Ridge is not supported by DOS or Windows.
HFS - The Hierarchical File System is the Macintosh disk format, also used for Mac CD-ROMs. It is legible only on Macintoshes, Amigas and the antique Apple IIgs. "Hybrid" discs, legible on all platforms, have an HFS section and an ISO-9660 section; Macintoshes can also read standard ISO-9660.
Joliet - Microsofts own standard that does much the same thing as Rock Ridge, but works with Windows 95 and maintains ISO-9660 compatibility, with truncated names.
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