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Making Space for Media: 
    Using DVD-RAM For External Storage  (5/2001)

    by Douglas Dixon

    Magnetic Storage: Zip and Jaz - CD-R and CD-RW
    LaCie - DVD-RAM

Are your disks filling up with video and audio files? Are you spending too much time shuffling old files between disks to try to recover some scratch space for your new work? How would you like a nice big convenient external drive with removable media that you could use to store and archive your work?

Relief is at hand: The growing popularity of hot-pluggable interfaces like USB and FireWire / 1394 has lead to the development of interesting new external storage products that can bring some sanity to dealing with large media files. No more opening up your computer to perform surgery to install a new drive, no more messing with SCSI connectors and termination, just plug and go, on PC or Macintosh. Even better, the newly expanded DVD-RAM format offers lots of storage -- up to 9.4 GB (billion bytes) per double-sided disc -- on a rugged medium that can be accessed and rewritten much like a normal hard disk.

External Interfaces

A key requirement for a storage solution is that it be available an external device. An external drive can be shared among multiple machines, easily replaced or upgraded, and avoids the pain and dangers of cracking the case to install a dedicated drive.

One easy solution for connecting an external drive is to use the parallel port. Parallel ports are used mostly for printers, but have been extended to provide two-way ("bi-directional") communication, with higher data rates. If your PC is configured properly, an enhanced (ECP/EPP) parallel port can provide a data rate of around 2 MB (million bytes) per second. But the parallel port often has to be shared, and is not a great solution for fast transfer of large video files.

A better solution for at least low-speed data transfer is to use the USB (Universal Serial Bus) ports included on newer PCs. USB was explicitly designed for sharing multiple devices such as scanners and input devices, and supports a data rate of 1.5 MB per second. USB also is a lot more convenient to use, since you can hot-swap the devices, plug in and remove them while the computer is running.

But the USB data rate is much slower than the older SCSI (Small Computer Systems Interface) interface, which was designed for high-performance disks. The SCSI interface can support multiple devices at data rates up to 20 to 40 MB per second. But while SCSI long has been the best available solution for external storage, it also can be a pain to use, with special 50-pin (or more) cables, and touchy cabling of a "chain" of devices with proper termination. While Apple has built in SCSI in the Macintosh line for years, using it on a PC typically also requires installing a SCSI adapter card.

These days a better solution is becoming available: the new FireWire, or IEEE 1394, interface, which combines the hot-plug convenience of USB with the fast data rates of SCSI. This interface is designed for high-speed data and digital video transfer, with data rates of up to 400 Mb (million bits) per second in the first versions, or 50 MB per second. Apple has popularized this interface under the FireWire name, and PC manufacturers are also starting to build it in to new systems especially for DV editing, or at least offer the option to have it pre-installed.

An even better solution for external drives is to provide multiple interfaces in a single device. Drives are available with both parallel and USB connections, and now both USB and FireWire. These drives can be used with a wider range of machines, both desktop and laptop, and provide the benefits of compatibility with older machines plus the possibility of using the newer faster, interfaces. Another alternative for laptops is to provide a PC card interface to plug in to a PCMCIA slot.

Magnetic Storage: Zip and Jaz

When thinking about adding more storage to a computer, the benchmark comparison is to just add another hard disk. These days you can pick up a 40 GB hard disk for about $150, or around $3.75 per GB. Our ideal storage solution would provide the convenient access of hard disks, but as a rugged and not too expensive removable media, and in an externally pluggable package.

One approach to providing the benefits of hard disk is to simply package magnetic media as removable storage, as Iomega has done with its Zip and Jaz drives. External Zip drives are available with a mixture of parallel, USB, FireWire, SCSI, and PCMCIA interfaces for $140 - $210. External Jaz drives are available with FireWire and SCSI interfaces for around $330. The Zip drives use 100 and 250 MB disks, with the 250 MB media priced around $12.50 each. The Jaz drives use 1 and 2 GB disks, with the 2 GB media priced around $100 each. Both end up at around $50 per GB, so they are great for sharing and transporting material and small archives, but pricey to use in larger quantities.

CD-R and CD-RW

Another obvious alternative for external storage is CD-R and CD-RW. The mass adoption and resulting manufacturing efficiencies have lowered write-once CD-R prices down to around 50 cents each, and rewritable CD-RW prices to around $1.20. Just the fact that these discs are commonly sold in large quantities (like a spindle of 100 discs) shows how popular they have become. At these prices, CD-R costs around 75 cents per GB, and CD-RW around $1.90. Now that's inexpensive media!

But, of course, our expectations have grown with the demands of digital video, so CD's now seem terribly small, since they hold only 650 MB of data. Full-resolution compressed video from a DV camcorder requires 25 Mb per second, or 3.1 MB, per second, or 187 MB per minute and almost 11 GB per hour. That's a lot of data: one CD can only store less than 3 1/2 minutes of DV video.

But the DV format is designed for editing, and uses relatively light compression of the individual frames. More aggressive compression for final production, like the MPEG-2 format used for DVD, compresses information across groups of frames, and can squeeze full-resolution video down to around 4.5 Mb per second or less, or 0.56 MB per second. This is conveniently just the right rate to fit a two-hour movie on a DVD, but also means you can save 19 1/4 minutes on a CD. And, of course, CD storage capacity is a good fit when you are working with Web video, with lower resolution and data rates and heavier compression.

CD-RW drives also have become quite portable. For example, the MicroSolutions Backpack 4x4x24 CD-RW drive is available with a parallel interface for $200, parallel and USB for $230, and parallel and PC Card for $240. (The three numbers --4x4x24 -- refer to the speed for writing CD-R, rewriting CD-RW and reading or playing, relative to the original 1X CD-ROMs at 150 KB per second.)

In January 2001, LaCie introduced the PocketDrive CD-RW, a 6" x 6" drive that fits in the palm of your hand. The LaCie drives include both USB and FireWire / IEEE 1394 connectors, which LaCie calls "U&I" dual-access (for USB and IEEE). The PocketCD-RW U&I 8x4x24 is available for $400. External SCSI CD-RW drives are also available (see


However, our storage demands for digital video continue to grow, and hundreds of megabytes on a CD is just not enough any more: We are looking for multiple gigabytes of space these days. Conveniently, the DVD format has arrived as a practical solution. Much of the industry finally has come together through the DVD Forum ( to agree on common formats and establish compatibility among them. There still are a lot of formats, but they each are targeted to different markets: DVD-Video for movies, DVD-Audio for music, DVD-ROM for prerecorded data, DVD-R for recording, DVD-RW for re-recordable / rewritable media, and DVD-RAM for rewritable data storage. These formats have also settled on a common capacity: 4.7 GB per disc, or 9.4 GB on a double-sided disc.

4.7 GB 
single sided

9.4 GB 
double sided
DVD-RAM media

LaCie DVD-RAM drive

The DVD-R and DVD-RW formats are similar to CD-R and CD-RW, in that they are designed for recording once (-R) or re-recording multiple times (-RW), on the order of a thousand read/write cycles. DVD-RAM (Random Access Memory) is another rewritable format that does not have a comparable CD format. DVD-RAM is designed for use as a reliable and high-capacity storage solution for multimedia and the enterprise. It has an estimated 30-year data life, can be written over 100,000 times, and incorporates error correction and defect management technology. To help achieve this reliability, the media is enclosed in a cartridge sleeve.

DVD-RAM offers the DVD form factor and capacity with the convenience of access of a floppy disk. It has been shipping in quantity for several years as PC data storage format, with one million units sold in 1998/99 and nearly 3.5 million projected to be sold in 2000. DVD-RAM media currently costs around $30 for a 4.7 GB disc, and $59 for a double-sided 9.6 GB disc, or around $6.25 per gigabyte. That's more than CD-RW at $1.90, but a lot less than removable magnetic media.

DVD-RAM Issues

LaCie and others offer external 4.7 / 9.4 GB DVD-RAM drives with a SCSI or FireWire / 1394 interface for around $700. Unfortunately, there are still some system compatibility issues to work out with these. The SCSI drives work with both Macintosh and PC, but the FireWire DVD-RAM drives are currently Mac only (although FireWire hard disks and CD-RW drives work fine on PC). DVD-RAM support on PCs requires additional drivers, which may be available by the time that you read this (so check the manufacturer's Web site). There are also some software compatibility issues with the new Windows Millennium release, so again check this with the drive manufacturer.

The other compatibility issue is between different DVD formats. The LaCie DVD-RAM drive can read (but not write) standard CD and DVD format media, including CD-ROM, CD Audio, CD-R, CD-RW, video CD, DVD-R, DVD-ROM and DVD video. However, the DVD-RAM discs cannot be read by most other players. For one thing, the DVD-RAM media is enclosed in a cartridge to protect it from dust, scratches, and other damage. Type I media (for double-sided discs) is permanently enclosed in a cartridge, and can only be read by a DVD-RAM drive. Type 2 media is designed so a single-sided disc can be removed from the cartridge, and can be read by some new DVD-RAM drives. To further confuse the issue, the older 2.6 and 5.2 GB DVD-RAM media is also still available.

But the great part about DVD-RAM is that you can use it just like any other disk, by just copying and removing files. You may need to install the appropriate drivers, and the discs also have to be initialized with special software to format them.

You also may be surprised at the difference between the theoretical and actual data rate with the DVD-RAM drives. The FireWire interface is designed to support up to 400 Mb or 50 MB per second, but these DVD-RAM drives are rated at 1.39 to 2.77 MB per second for DVD-RAM transfer (but up to 3.4 to 8.3 for DVD-ROM). Part of the slowdown with DVD-RAM is the extra error correction and defect management designed into the format. You can increase the data rate to around 4 MB per second by disabling write verify.

Got Storage?

DVD-RAM clearly offers almost the best of all worlds as an external removable storage media. It's pretty big (4.7 to 9.6 GB), reliable and rugged (you do not have to keep it away from magnets), reasonably priced ($700 for the drive and $30 to $59 for the media), and can be accessed much like a standard disk.

While this is not yet at the mass-market price point of CD-R, it is getting quite interesting. Another alternative for DVD storage is the new Pioneer DVD-R / CD-RW drive, which should be available as an internal IDE drive in Q2 2001 for a suggested price of $995, with the DVD-R media price below $10. DVD-R is an attractive option for burning archives, and for compatibility with a wide range of DVD-Video players, but it cannot be used as a hard disk replacement like DVD-RAM.

The new FireWire / 1394 and USB interfaces also offer a convenient approach to connecting up external drives without even the hassle of SCSI. There are even adapters available for converting older drives to the newer interfaces. For example, Iomega sells adaptors for converting SCSI drives like the Jaz to USB for $80 and to FireWire for $100.

So stop fighting for disk space and plug in to one of these external removable storage solutions. You can have free space, and archive too!

For all the gory detail about the DVD format, technical details, and products, see the DVD FAQ (Frequently Asked Questions), by Jim Taylor, author of "DVD Demystified" (McGraw-Hill, December 2000) at


LaCie CD and DVD Drives

DVD Forum

DVD FAQ - Jim Taylor, DVD Demystified