Data Storage for Mobile Devices
The increasing sophistication of mobile electronic devices and the size of rich media files is leading to ever greater demands on mobile data storage. We will continue to see a variety of data storage products filling the needs of this industry. We are also likely to see 1 a continuation of embedded and removable data storage solutions offering advantages.
One of the most critical design factors affecting the shows expected average data storage capacity performance of mobile devices is their data storage requirements for various mobile device applications. capability. The mobile environment has many demanding There are several types of non-volatile data-storage requirements, including control of power consumption to products that have been developed for mobile electronic meet the needs of battery-powered devices; physical size to devices. These include several types of magnetic storage fit into small electronic devices and possible removability; devices such as small hard-disk drives, tapes, floppy disks, resistance to severe environmental factors such as shock, and magnetic cards, as well as small optical devices and, of vibration, and temperature; and, of course, growing course, many varieties of flash semiconductor memory. data-storage capacity requirements to meet the needs of An additional factor driving the growth of data storage rich multimedia content. In addition, for many consumer on mobile devices is the growing trend toward additional White devices the price of the data storage is an important factor features incorporated into individual electronic devices. in the total cost of the product, making this market very Devices such as radios and GPS are becoming intellectual Paper sensitive to the price of data storage products. property that can be incorporated into an electronic chip as needed (with antennas or other required peripheral devices Thomas M. Coughlin Drivers for Mobile Device Data Storage also incorporated into the overall product design) or to add Coughlin Associates Electronic devices are shrinking in size to meet the needs greater attractiveness to customers due to greater overall of a more mobile population. Fewer people are necessary product functionality. Future incorporation of voice recog- to perform what once were multiple jobs. This is enabled nition into mobile devices (needed to create real hands-off by increasing connectivity to colleagues and greater usage) will require very large amounts of local data storage. access to corporate (intranet) and cultural (Internet) information sources. This more-connected population Choosing Mobile Data Storage Devices has also become a more-mobile population. Workers and Similar to other computer systems, we can organize the population in general are becoming dependent upon mobile data storage requirements in a performance and the electronic devices that they carry with them for work, price hierarchy. Figure 2 shows a mobile data storage personal communication, and entertainment purposes. product hierarchy. Information needed to boot up the People are becoming mobile nodes in a worldwide, mobile device and for immediate fast processing are connected information and entertainment network. With stored in ROM and RAM semiconductor memory. This is the development of flexible display technologies and the fastest and most expensive memory used in these ever-smaller computer-based devices, we are only a few devices. In addition, RAM is volatile memory, meaning years away from incorporating those computer-based the data is not stored after the power is turned off. devices, including data storage, into the clothing that we wear or even in our bodies. Thomas M. Coughlin is president of Coughlin Associates Data storage plays a large role in creating this (www.tomcoughlin.com), a data storage consulting firm mobile electronic infrastructure. The growth in mobile specializing in data storage components, systems, and software information traffic, combined with limited wireless data used in consumer electronic, enterprise, and entertainment rates, often interrupted wireless service, and the large file applications. He has more than 20 years of industrial experience in data storage, product development, program management, sizes of MP3, MPEG-4, and other multimedia content, and market and technology assessment. Mr. Coughlin is a senior makes local data-storage cache an important factor in the member of the IEEE, a founding member of the Server Blade delivery of high-quality multimedia experiences. Figure 1 Trade Association, and a member of IDEMA, ACM, and APS.
www.MobileImperative.com Technologies (formerly IBM) MicroDrive (27mm) 600 PDAs and and the Toshiba 1.8-inch (48mm) embedded or Handhelds removable hard-disk drives. These have even lower 500 Digital Still cost per megabyte, but because of the fixed costs Cameras of making the hard-disk drive, they start out at a higher part price than lower-capacity flash memory 400 Digital Video or even the optical disks, magnetic strip, or tape technologies (described next). Thus hard-disk drives 300 Digital Audio are more likely to find their greatest use where the
MegaBytes size or number of the data files being handled 200 Flash Drives requires it (such as video files or an MP3 jukebox). Finally we must consider tape-, floppy-, and 100 GPS magnetic-strip card-based data storage products. Most digital video cameras still use tape, and some 0 of these tapes are quite small, such as the MiniDV Mobile Phones 2001 2002 2003 2004 2005 tape cassette (2.6 x 1.9 x 0.5 inches). The cost of tape is quite low, and the capacity can be large, but Figure 1: Average Megabyte Requirements the access time to data can be several minutes. Floppy capacities are rather low, although higher- Cost/Speed capacity floppies are possible. An IEEE 802.11b or WiFi wireless network Volatile Storage has a rated data rate of about 11 million bits per $0.25/MB second (Mbps) depending upon the proximity of 20 ns RAM/ROM the wireless network member to the WiFi hub. This channel bandwidth is available to be shared by $0.25/MB all the members of the local wireless network. 60 ms Flash Memory Non- (removable/non-removable) Volatile However, an MPEG-4 video stream may require $0.04/MB Tiny Optical ROM/WORM Storage 1.45 million bytes per second (MBps) or 11.6 10 ms (removable) Mbps. Thus a live MPEG-4 stream will more than $0.02/MB Micro or Pico HDD consume the bandwidth of a single WiFi channel. 12 ms Mass Storage (removable or embedded) For this reason large digital content such $0.01/MB as video will need to stream from a large local Small Tape or Floppy 120 sec Mass Storage (removable) memory cache such as a small hard-disk drive, optical disk, or even a small magnetic tape. This need for large local memory cache is even greater Capacity because of the frequent interruptions in a wireless Figure 2: Mobile Data Storage Hierarchy network and the disastrous effect such interruptions have on a live video stream. To use such a large The lower part of the hierarchy pyramid shows A small optical device such as the DataPlay memory cache requires ways to decrease potential non-volatile memory; the data in these devices is WORM (write once, read many times) drive uses a issues such as power usage. Figure 3 shows a retained even after the power is turned off. Flash 34mm diameter optical disk that can be written on schematic for a portable wireless multimedia device memory can be embedded in the device or can both sides (for a total of 500MB of data storage). using a small disk drive that would download be removable, and the removable varieties have a Because of the small size of the optical components content over the Web or at high-speed multimedia great many form factors, from PCMCIA devices developed for this drive, the average time to access kiosks. The drawing also shows download times to ones about the size of a nickel. Flash memory data is much less than on the type of CD or DVD for a two-hour movie at various transfer data rates. is very popular in mobile devices due to its drives used in desktop or laptop computers. The price Mass and volume are other important ruggedness and small size. Although the price per of storage on this disk is much less than that of a flash characteristics for a storage device in a mobile megabyte is not as low as alternative devices the memory, but the price of the optical drive (currently electronic product. Figure 4 shows the various most popular capacities sell for $50 or less and about $50) must also be taken into consideration. removable mobile memory form factors are large enough (128MB or less, currently) to Next in the data storage hierarchy are small produced by flash memory card and hard-disk be of use for many applications. hard-disk drives such as the Hitachi Global Storage drive vendors. There are additional, even
42 www.MobileImperative.com Portable Wireless Multimedia Device
Antenna
High-speed Processor, MPEG4 Head mounted Direct-view LCD wireless modem decoder, media display screen and radio content protection
Y Cr Cb RGB A/V Docking Bulk storage Docking S-Video Battery >10GB interface station NTSC/PAL Line-level audio SPDIF
Desired read and write speeds Download time Download time differ by a factor of 200 to 500 Mbps (seconds) (minutes) 1000 16 0.3 500 32 0.5 60 MBs/sec 200 80 1.3 39 MBs/sec 100 160 2.7 50 320 5.3 20 800 13.3 10 1600 26.7 IBM 1GB Microdrive 5 3200 53.3
Figure 3: Wireless Personal Multimedia Device Using a Small Hard-Disk Drive smaller, form factor products due out soon. may require a larger volume in the host device into the host device, since any shock will Besides these products, USB-interface flash to support them. be distributed and absorbed by the product memory products offering current capacities of Nevertheless, these products may be advanta- enclosure. An important consideration in easily tens or hundreds of megabytes of data storage geous for an application requiring frequent media using an embedded data storage device is for have become quite popular and may eventually change, such as content distribution. It might even the manufacturer to include standard mounting replace floppy drives as their price declines. be that a higher-capacity non-removable storage hardware capability such as standard threaded Little hard-disk drives, like flash memory, are device may be combined with a lower-capacity screw holes in the device casing. Some of the self contained and require only electrical removable device in some mobile application, similar initial efforts to use small hard-disk drives in connections to read them. Thus the size of the to desktop and laptop computers that have hard-disk audio jukebox products with 1.8-inch disk drives storage device is roughly the size required inside drives as well as CD/DVD or floppy drives. had to use tape to secure the drive. of the host device to support it. Tape, floppies, The first commercial examples of an and magnetic strip cards require a drive, like the Embedded vs. Removable Storage embedded hard drive inside of consumer optical media, which adds extra cost and bulk to An embedded data storage device is one that is electronic products are various audio jukebox the mobile product. permanently a part of the electronics in the host products using 1.8-inch or 2.5-inch disk drives. On the other hand, optical, floppy, tape, or device. Embedding a data storage device into the On an even smaller scale, a new company called magnetic strip media can be much cheaper for a host product results in a more compact and Cornice will be selling embedded sub-1.8-inch given capacity (less than $15 each for the least mechanically simpler device and better protection disk drives in 2003. Cornice is offering a small, capacity) than a flash card or magnetic hard disk. from the outside environment. In addition, the magnetic-disk-drive-based product with a current Thus, drive-dependent products offer lower ruggedness of many data storage products, such as a formatted capacity of 1.5 GB that is intended to media costs but have a disadvantage in that they small hard-disk drive, is enhanced when it is built be embedded in host mobile products and that
www.MobileImperative.com 43 information on a medium by either melting a pit Storage Device Size into a plastic layer or by magnetically recording information on a suitable surface. There are also PC Card (PCMCIA) a number of new semiconductor non-volatile memory products in development. • Type I 85.6 x 54.0 x 3.3 mm Magnetic random-access memory (MRAM) is being pursued by several companies (notably 85.6 x 54.0 x 5.0 mm • Type II IBM, Cypress, and Motorola). These products store • Type III 85.6 x 54.0 x 10.5 mm information in a magnetic tunnel junction at the interface of write and read wires on a chip surface. On the other hand, the current data-storage technologies haven’t run out of gas. Flash, Microdrive 42.8 x 36.4 x 5.0 mm magnetic, and optical data-storage technologies have their own technology roadmaps and can be extended considerably beyond their current data CompactFlash Cards densities to allow a lot of information to be stored • Type I 42.8 x 36.4 x 3.3 mm on much smaller devices. Recently, Mark Kryder of Seagate Research said that with a combination of advanced head, medium, and channel tech- • Type II 42.8 x 36.4 x 5.0 mm nology, magnetic recording could probably be extended to areal densities of 50 terabits per SmartMedia Card 45 x 37 x 0.76 mm square inch. For comparison, common disk-drive product areal densities in 2002 were less than 50 gigabits per square inch, 1,000 times less. Multimedia Card 32 x 24 x 1.4 mm Within a few years we may see data-storage devices so small that they can be incorporated as part of a personal electronic network built SD Card 32 x 24 x 2.1 mm into the fabric of a person’s clothing and perhaps powered by the heat generated by their host. This would be nearly the ultimate in portable electronics. Memory Stick 21 x 50 x 2.8 mm Summary Different data storage devices offer various combinations of features that can be important Miniature Card 38 x 33 x 3.5 mm to the designer of a portable electronic device. For this reason it is likely that we will continue Figure 4: Mobile Memory Form Factors to see a variety of data storage products filling the needs of this industry. We are also likely to can be produced at much lower cost than the an embedded data storage product may allow see a continuation of embedded and removable current Hitachi Global Storage Technologies for memory expansion or file portability by data storage solutions offering advantages for MicroDrive. Embedded hard-disk products using providing removable data storage as well. various sorts of uses. One thing appears to be 1.8-inch or smaller disk drives will be included clear. The more connected people become with in some of the new mobile personal-video-player Future Mobile Storage Devices wireless and wired networks, the more digital products that will be introduced in 2003. Many types of robust mobile data storage data they and their machines will generate, Flash memory is often embedded inside devices are in development in R&D laboratories requiring ever more data storage. This need for mobile electronic products requiring lower throughout the world. These include new optical greater data storage will be driven by the desire capacities than an embedded hard drive. These storage technologies such as holographic data of consumers for rich multimedia files and by may be found in many types of portable MP3 storage or probe-based data storage technologies the decreasing price of data storage and portable players, smart phones, and PDAs. A device with that use a gang of several tiny probes to record electronic products. ■
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