Storage

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In this Learning Center chapter on Storage, we’ll take a look at how programs and data are stored on handheld computers. We’ll cover the two main types of storage: internal storage, commonly referred to as main memory, and external storage, typically found in removable storage cards.

Introduction to storage

Does a computer really need a way to store data? No, not really. After all, the three basics of computing are inputting data, processing it, and eventually outputting the results. There’s nothing in there about storage. But from a purely practical viewpoint, a method for storing information can be crucial. Otherwise, each time you decide to do something you’d have to enter the data you wish to process and the program code that processes it. Imagine having to enter the hundreds of lines of code for Microsoft Excel every time you wanted to create a spreadsheet. Not very efficient, is it?

Charles Babbage faced that problem in the 1830′s while working on an invention he called the Analytical Engine. He turned to a method invented by Frenchman Joseph-Marie Jacquard for his automated weaving loom (see photo at right, courtesy Smithsonian Institute). Jacquard used perforated cards to convey the weaving pattern to the loom. Babbage figured that the same punched card method could be used in his early computer, which MIT’s Herman Hollerith went on to perfect for storing census data for the U.S. Census department in 1890.

Since then we’ve moved from purely mechanical forms of storage, such as the punched card and its cousin punched tape, to electromagnetic and other forms of storage. Today we have magnetic disk, magnetic tape, solid state disks, optical disks, and holographic storage. Plus, we’ve now got Storage on computer chips built into our computers — commonly called internal storage, or main memory — as well as on separate storage devices and media, such as disk drives and Compact Disks, or CDs.

Internal Storage, or Main Memory

Built-in storage, or main memory, as it commonly referred to, comes in two flavors: ROM and RAM.

ROM. ROM is short for read-only memory. It refers to a memory chip that permanently stores instructions and data, without requiring power. Its contents are written, or “burned,” onto the chip at the time of manufacture, but cannot be changed thereafter, hence the name read-only. (We’ll soon find out that there is an exception to this rule.)

This is an important concept in handheld computing because for most handhelds the operating system is stored, and sometimes even executed, in ROM — quite different from your typical desktop computer which stores the OS on its hard drive and loads it into main memory each time you boot up. So, in order to upgrade your handheld’s operating system, you must replace the contents of its ROM — not an easy proposition.

For some of the early PDAs, including the original Palm Pilots, the early Handspring Visors, and Compaq’s Aero Palm-size PC, this means replacing the ROM chip. That is, if the manufacturer offers an upgraded ROM — many simply do not.

A more recent alternative for PDA Manufacturers (remember earlier when we mentioned the exception to the rule) is to use "flash memory" ROM chips, which can be upgraded programmatically rather than requiring replacement. In fact, its name was coined by its inventor, Toshiba, because it could be erased "in a flash." Still, like standard ROM, flash ROM is non-volatile, meaning it does not lose its contents when power is removed.

Palm was the first handheld company to use flash ROM, starting with its Palm III, while Compaq was the first Pocket PC vendor to offer it in its iPAQ handheld three years later. While most of the newer handhelds use flash ROM, some still do not. That’s often because standard ROM is less expensive than flash ROM.

Recently, a new type of Flash ROM called NAND Flash ROM (as opposed to the more common NOR Flash ROM) has begun to appear in handheld computers. NAND Flash ROM was developed to serve as a disk-like storage medium for digital cameras and PDAs. Its advantages are that it’s cheaper, higher capacity, and lasts ten times longer than NOR Flash ROM. Its disadvantage is that instructions cannot be directly executed in ROM, something called execute in place, or XIP. Instead, the operating system’s instructions must be read from NAND Flash ROM into main memory and executed there, similar to your desktop computer’s hard disk and main memory. Therefore, a chunk of main memory is reserved for this purpose, meaning you get less memory for your programs and data.

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So, how much ROM do you need? Well, you obviously need enough ROM to hold the operating system, as well as any other programs that the manufacturer wants to include in it. Also, some PDA manufacturers have starting using portions of ROM for non-volatile storage of user data, so that if you lose power or need to hard reset your device, you won’t lose your data.

Finally, is flash ROM a requirement when deciding on a new handheld computer? Not exactly. Keep in mind that flash ROM is important only if you are fairly certain that you’ll be upgrading the operating system on your device at some time, otherwise it doesn’t really matter. Also, just because a device has flash ROM doesn’t necessarily mean that its manufacturer will provide a ROM upgrade when a new version of the operating system is released.

RAM. RAM, meanwhile, is short for random access memory. It is a group of memory chips which function as the computer’s primary workspace. It is used to hold programs and data files. In many operating systems, RAM is also called "main memory."

RAM is different from ROM in that it is volatile. In other words, it requires power to maintain its contents. Just pull the batteries out of your device for a while and you’ll see the practical implications of this. Still, RAM has something over ROM: its contents are easily modifiable.

In general, the more RAM the less you’ll have to rely on storage cards, and often times the better and faster your device will perform. Still, storage is storage, and a storage card is just as good as RAM for storing data.

Storage Cards

There are several different types of storage cards: CompactFlash (CF), PC Cards, MultiMediaCard (MMC), Secure Digital (SD), Microdrive, SmartMedia, and Memory Stick (MS).

PC Cards. PC Cards, commonly referred to as PCMCIA cards, came about in the late 1980′s as laptop computers and mobile computing became popular. PC Cards are credit card-sized integrated circuit devices that are rugged and relatively low power (as compared to typical PC storage and I/O peripherals). This makes them perfect for, among other things, storing data that you’d like to take with you.

PC Cards are manufactured by hundreds of manufacturers around standards developed by the Personal Computer Memory Card International Association (PCMCIA) and they come in three official (Type I, II, and III) and one unofficial (Toshiba’s Type IV card) types.

PC Cards are 16-bit plug-and-play devices measuring 3.37" long by 2.126" wide. They use a 68-pin connector, with cards being the female end of this pin-and-plug interface.

Several models of Pocket PCs can use PC Cards, although only the @migo, from the defunct UR There International, can do it without the use of a separately purchased add-on accessory, such as an expansion pack or sleeve. However, PC Cards are not recommended for handheld computers since they draw too much power.

Largest capacity: 15 gigabytes
Cost per megabyte: $0.09 – $0.15
Pros: Highest capacity; Lowest cost per megabyte
Cons: Relatively large; Relatively power hungry

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CompactFlash. CompactFlash (CF) storage cards, first introduced in 1994 by SanDisk, are the most widespread removable storage devices found in PDAs, although SecureDigital is now a close second. They are fast, lightweight, matchbook-sized removable mass storage devices that use flash technology, a non-volatile storage solution that can retain data indefinitely, even without power. They can be used in a variety of consumer devices, including digital cameras and handheld computers. In fact, CompactFlash is supported in most platforms and operation systems that support the PCMCIA ATA standard.

CompactFlash storage cards for handheld computers are available from more than 40 companies, in capacities up to three gigabytes, and costing on average between US$0.20-US$0.60 per megabyte.

While CompactFlash storage cards are more expensive than conventional disk drives, they do have several advantages. For one thing, they are solid-state devices, meaning they contain no moving parts. This provides greater data protection and less chance of mechanical problems. Also, CF cards use minimal power and are rugged. They run at 3.3V or 5V with a single power supply and consume less than five percent of the power required to operate a conventional disk drive. And CF cards can typically withstand a 10-foot drop. With typical usage, a CF card can last more than 100 years with no loss or deterioration of data.

However, programs cannot be run directly from CompactFlash storage cards. Instead, they are loaded into RAM for execution. This results in a minimal delay over programs that reside in RAM. The connector used with CompactFlash is similar to the PC Card connector, but with only 50 rather than 68 pins. Still, it conforms to ATA specs and can be easily slipped into a passive 68-pin Type II adapter card that fully meets PCMCIA electrical and mechanical interface specifications.

CompactFlash is a registered trademark licensed through the CompactFlash Association.

Largest capacity: 3 gigabytes
Cost per megabyte: $0.20 – $0.60
Pros: Best combination of form, function and price
Cons: Not as small as MMC and SD, although new Ultra Compact Flash cards come close

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MultiMediaCard. MultiMediaCard cards are lightweight, postage stamp-sized storage cards that use flash memory. They are currently available in capacities up to 128 megabyes. They can be used in most of the latest Palm Powered devices and Pocket PCs. MultiMediaCard cards use 7 metal connector contacts rather than pins-and-plugs so they are less likely to be damaged in transport or insertion and removal.

Largest capacity: 128 megabytes
Cost per megabyte: $0.30 – $1.25
Pros: Smallest and lightest of all removable media
Cons: Smaller maximum capacity than CompactFlash

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Reduced Size MultiMediaCard. The MultiMediaCard Association (MMCA) has approved a standard for a smaller version of the MultiMedia card. The new Reduced Size MultiMediaCard (RS-MMC) is approximately one-half the size of the standard MultiMediaCard. These were designed for mobile phones where space is at a premium but could potentially be used in handhelds, too.

The new cards will be manufactured and marketed by various members of the MMCA. RS-MMC cards are available in 16 to 64 MB capacities, and 128 MB and 256 MB ones will be available sometime in 2003.

A standard MMC card is 24mm by 32mm by 1.4mm, while a RS-MMC card is 24mm by 18mm by 1.4mm. A reduced size card can be used in a standard MMC slot with a mechanical expander, and a standard MMC card can be used in a slot intended for a RS-MMC card, however it will protrude.

Largest capacity: 64 megabytes
Cost per megabyte: $0.50 – $1.50
Pros: Small and lightweight
Cons: Small capacity

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Secure Digital. Secure Digital cards are lightweight, postage stamp-sized storage cards that use flash memory. They are currently available in capacities up to 512 megabyes, but are expected to grow to 1 gigabyte before the end of the year. They can be used in most of the latest Palm Powered devices and Pocket PCs. Secure Digital cards (which differ from MultiMediaCard cards in that they provide for secure distribution of content, such as digital music and electronic books) use 9 metal connector contacts rather than pins-and-plugs so they are less likely to be damaged in transport or insertion and removal.

Smaller and lighter miniSD cards (see photo at right) are being developed for use in smart cellular telephones and MP3 players. Half the size and weight, they will have a maximum capacity of 256MB.

Largest capacity: 512 megabytes
Cost per megabyte: $0.25 – $0.70
Pros: Small and lightweight; erasure prevention switch
Cons: Smaller maximum capacity than CompactFlash

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MemoryStick. Smaller than a stick of gum, Sony’s Memory Stick is currently used in several consumer products, including digital cameras, audio devices and more recently its Palm OS-based Sony Clie handheld computers. But some industry folks wonder whether other PDA Manufacturers would ever go with Sony’s Memory Stick. After all, would it really want to have a critical component of its device produced by a direct competitor?

Memory Sticks are currently available in four formats — Standard, Pro, Select, and MagicGate — and in two sizes — Standard and Duo — and in capacities up to 1 gigabyte, and cost between US$0.40 and US$0.70 per megabyte. It uses a 10-contact connector and can read data at speeds up to 2.45 MB per second.

Largest capacity: 1 gigabyte
Cost per megabyte: $0.40 – $0.70
Pros: Small; erasure prevention switch; no connector pins
Cons: Non-standard

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Microdrive. IBM, inventor of the Winchester magnetic disk technology, has taken disk storage miniaturization to new levels with its microdrives. These matchbook-sized CompactFlash devices contain an actual mechanical disk drive rather than flash memory chips. The upside is that they cost less than typical chip-based storage cards, generally between US$0.15 and US$0.20 per megabyte. However, the downside is that they draw more power and generate more heat. Also, since they have moving parts, they’re likely to experience more mechanical problems than CompactFlash storage cards.

Recently, other companies in addition to IBM, including Magicstor, have released microdrives.

Largest capacity: 2.4 gigabytes
Cost per megabyte: $0.15 – $0.20
Pros: Low cost per megabyte
Cons: Power hungry; more susceptible to damage because it contains moving parts

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SpringBoard. HandSpring introduced an expansion method with its Visor line of Palm OS-based PDAs called Springboard. Springboard resembles the cartridge and modular connector system used in the Nintendo’s GameBoy systems. One of the first Springboard modules to be released was the 8 megabyte Flash Module (US$79.95). It uses non-volatile flash ROM, so it can be removed without losing its data. On the technical side, Springboards use a 16-bit interface (SmartMedia and Compact Flash have 8-bit interfaces), so they have a higher bus speed.

HandSpring has discontinued using the SpringBoard technology in its products.

Largest capacity: 16 megabytes
Cost per megabyte: $3.75 – $10.00
Pros: True plug-and-play (i.e. no drivers need to be installed)
Cons: Expensive; No longer supported

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SmartMedia. Used primarily in digital cameras, SmartMedia cards are thinner and lighter than most other storage cards. In fact, at 0.76 millimeters, they are approximately 1/4 the thickness of a CompactFlash card, and weigh just 2 grams.

Like CompactFlash cards, SmartMedia cards use NAND-type flash memory — 16MB, 32MB, and 64MB chips — for storage. But unlike CompactFlash they do not have a controller on board; rather, the controller is part of the slot built into the device that uses it. SmartMedia cards are also very power efficient drawing just 3.3V of power, and use a flat electrode terminal with 22 contact points rather than protruding pins.

Currently, none of the Pocket PCs or Palm OS devices on the market have slots to accomodate SmartMedia cards. However, there is a SmartMedia SpringBoard adapter for the Handspring Visor available from MemPlug and a snap-in module, called the axxPac, that fits into the expansion slot on the Palm IIIx and enables it to use SmartMedia cards.

SmartMedia is a trademark of the Toshiba Corporation.

Largest capacity: 128 megabytes
Cost per megabyte: $0.25 – $0.50
Pros: Thin; no connector pins to break; low power draw
Cons: Low capacity; does not contain controller

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xD-Picture Card. Developed jointly by Olympus and Fuji for use in digital cameras, xD-Picture Cards are extremely small and lightweight, and very power efficient. Unlike most storage cards used in handheld computers, xD-Picture Cards do not have a controller on board; rather, the controller is part of the slot built into the device that uses it.

Currently, none of the Pocket PCs or Palm OS devices on the market have slots to accomodate xD Picture Cards, and since the cards do not contain a built-in controller it is highly unlikely they ever will.

Largest capacity: 512 megabytes
Cost per megabyte: $0.50 – $0.80
Pros: Thin; fast write times; low power draw
Cons: Does not contain controller

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The Future of Storage

Secure Digital will continue to make tremendous inroads over the next two years and bypass CompactFlash as the leader in Storage cards by 2005. MemoryStick usage will also grow as Sony promotes its use across its entire consumer products line.

And in the distant future there’s optical and holographic storage, which we’ll cover when the time arrives.

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