Q: What is the difference between SRAM and Flash RAM?
A: SRAM cards use solid-state Static RAM to store information; they are generally limited to 4MB. SRAM is capable of storing data using a very small amount of charge, but requires constant refreshing in order to retain the data. SRAM cards use a tiny coin cell battery, which typically lasts about two years, to keep the data in memory; the manufacturers recommend replacing it once every year to be safe, because if the battery goes, so does the card's contents (though you'll get a few minutes to insert a new battery). An SRAM card never wears out and theoretically could last forever, needing only a new battery every year or two. SRAM is quite expensive, so a typical SRAM card costs more per megabyte than a Flash RAM card. The advantage of SRAM is that it doesn't require as much power to write to as Flash RAM.

Flash RAM is a type of Erasable Programmable Read-Only Memory (EPROM); they can be in excess of 20MB. When writing information to a Flash RAM card, the data is "burned in" (i.e., the Flash chips are physically modified). To write to the same area again, it must be "flashed," or cleared of the previously stored data (this process is automatic). Eventually the chips get used up and you can no longer write new data to the card. The number of disk writes that can take place before this happens is in the hundreds of thousands, so under normal usage a Flash card has a life expectancy of several years. Writing to Flash RAM requires considerably more power than SRAM cards. Reading from memory, however, requires about the same amount of power as SRAM. The advantage of Flash RAM is that it is less expensive per megabyte than SRAM. In addition, Flash cards are non-volatile, meaning they do not need any source of power to retain data in memory. Thus, you do not have to worry about losing all your data because the battery ran out of juice.

The reason why Flash RAM cards are not recommended for the OmniGo 100/120 is that they demand a significant electrical charge to initialize. There's actually a driver on the OmniGo that supports many Flash cards, and if your batteries are brand new, you might be able to insert and use one for a short while. However, when the batteries are down by even one third or so, they might not have enough power to initialize the card, and that could result in data loss both on the card and on the OmniGo itself. There may be some new low-power Flash cards that work around the power issue, but as of this writing, Hewlett-Packard has not certified those cards for the OmniGo (with the exception of CompactFlash cards), so your warranty for their use resides with the cards' manufacturer.

Q: What are CompactFlash cards?
A: CompactFlash cards are similar to Flash RAM cards, but they are much more "compact"—about the size of a matchbook. SanDisk, one of the first manufacturers to endorse CompactFlash, claims that it offers other benefits over standard Flash RAM; you can read more about it at their website under Support. Only the OmniGo 120 supports CompactFlash cards out of the box (with a PCMCIA adapter), though it might be possible to use these cards in the OmniGo 100 by copying the required driver(s) from the 120.

Q: Why don't all SRAM and Flash RAM cards work on the OmniGo?
A: Like many PDA's, the OmniGo can only accept certain kinds of memory cards. This is partly because not all cards are compatible with the OmniGo software and partly because the OmniGo can't supply enough power to PCMCIA cards designed for larger machines. Your best bet for finding a compatible SRAM or Flash RAM card is to read all available online forums for posts relating to other users' experience with that particular brand and model, and ask the card supplier if it has been successfully tested on the OmniGo. Most SRAM and ATA Flash cards should work in the OmniGo without any special drivers. If you plan to purchase a Flash card, make sure that it is "ATA" or comes with an OmniGo-compatible driver. (See the notice in the answer to the first question if you're considering ATA Flash cards.)

One trick that has been reported as occasionally successful in getting non-responsive SRAM cards to work in the OmniGo is to remove their batteries for at least 24 hours, replace them with fresh ones, and then reformat the cards. Apparently the SRAM card's non-removable internal bridge battery sometimes needs to be fully discharged before reformatting can take place.

Q: Why does my OmniGo take up to 5 seconds to react after being turned on?
A: When the OmniGo is turned on, it scans your SRAM card to make sure that it is valid. With some SRAM cards this can cause up to a 5-second delay. Cards that exhibit this problem lack attribute memory. To guarantee that your SRAM card will not have this problem, make sure to specify that it must have 2KB of attribute memory when you make a purchase. (Flash RAM cards do not suffer this delay.)

Q: Where can I purchase memory cards for the OmniGo?
A: You can usually purchase memory cards for the OmniGo from any vendor that carries PDA's, or you can order directly from the card manufacturers (see the Links page). Most OmniGo users recommend ordering SRAM cards from Pretec. Other SRAM cards that have been proven to work in the OmniGo include those from ACE Technologies and MagicRAM. When making a purchase, make sure to specify that you want an SRAM card with 2KB of attribute memory in order to prevent access delays (see previous question).

If you're in the market for a Flash RAM card, you can usually find them where SRAM cards are sold. Pretec carries a selection of Flash cards that work in the OmniGo. Cards from MagicRAM require a special driver, which you can download from this site's Software page or directly from their website. SanDisk also makes Flash cards, along with the new CompactFlash cards supported by the OmniGo 120. Before you purchase a Flash card, make sure that it follows the ATA standard. (See the notice in the answer to the first question if you're considering ATA Flash cards.)

Q: Can I increase storage with a file/disk compressor?
A: Yes! The GEOS operating system used in the OmniGo relies on DOS for all file and disk functions; you can take advantage of this to increase storage capacity by using DOS file and disk compressors. Marcus Groeber has successfully installed the dLite runtime file decompressor. Stacker, a disk compressor, has also been successfully used on the OmniGo. Instructions on how to install and use dLite and Stacker can be found on the Tips page.