RAM can be compared to a person's short-term memory and the hard disk to the long-term memory. The short-term  memory focuses on work at hand, but can only keep so many facts in view at one time. If short-term memory fills up, your brain sometimes is able to refresh it from facts stored in long-term memory. A computer also works this way. If RAM fills up, the processor needs to continually go to the hard disk to overlay old data in RAM with new, slowing down the computer's operation. Unlike the hard disk which can become completely full of data so that it won't accept any more, RAM never runs out of memory. It keeps operating, but much more slowly than you may want it to.

How Big is RAM?

   RAM is small, both in physical size (it's stored in microchips) and in the amount of data it can hold. It's much smaller than your hard disk. A typical computer may come with 32 million bytes of RAM and a hard disk that can hold 4 billion bytes. RAM comes in the form of "discrete" (meaning separate) microchips and also in the form of modules that plug into holes in the computer's motherboard. These holes connect through a bus or set of electrical paths to the processor. The hard drive, on the other hand, stores data on a magnetized surface that looks like a phonograph record.

   Today's personal computers come with 16 or more megabytes of RAM, usually increasing in multiples of 8 megabytes. Users of graphic applications usually need 32 or 64 megabytes of memory. Most personal computers are designed to allow you to add additional RAM modules up to a certain limit (for example, up to 64 or 128 megabytes). Having more RAM in your computer reduces the number of times that the computer processor has to read data in from your hard disk, an operation that takes much longer than reading data from RAM. (RAM access time is in nanoseconds; hard disk access time is in milliseconds.)

Why Random Access?

   RAM is called "random access" because any storage location can be accessed directly. Originally, the term distinguished regular core memory from offline memory, usually on magnetic tape in which an item of data could only be accessed by starting from the beginning of the tape and finding an address sequentially. Perhaps it should have been called "nonsequential memory" because RAM access is hardly random. RAM is organized and controlled in a way that enables data to be stored and retrieved directly to specific locations. A term IBM has preferred is direct access storage or memory. Note that other forms of storage such as the hard disk and CD-ROM are also accessed directly (or "randomly") but the term random access is not applied to these forms of storage.

   In addition to disk, floppy disk, and CD-ROM storage, another important form of storage is read-only memory (ROM), a more expensive kind of memory that retains data even when the computer is turned off. Every computer comes with a small amount of ROM that holds just enough programming so that the operating system can be loaded into RAM each time the computer is turned on.

   A remote access server is the computer and associated software that is set up to handle users seeking access to network remotely. Sometimes called a communication server, a remote access server usually includes or is associated with a firewall server to ensure security and a router that can forward the remote access request to another part of the corporate network.

   A remote access server may include or work with a modem pool manager so that a small group of modems can be shared among a large number of intermittently present remote access users.

   The Rocket eBook holds up to 4,000 pages of text (roughly 10 novels), and any of these can be replaced at any time by downloading new books or other reading matter from Web sites. To recharge the battery and to connect to a PC, the Rocket eBook comes with a "cradle" that connects to a power supply and, through a serial connection, to your PC.

   NuvoMedia, makers of Rocket eBook, says that the 22-ounce device's ergonomically rounded edges are easy to hold and its controls are natural. You can turn pages, do highlighting, annotate, search, and create bookmarks. You can also adjust type size to your preference and it has been designed to accommodate those who are left-handed.

   According to an article in Wired, Martin Eberhard, a hardware engineer, and Ralf Grone, an industrial designer, started with a prototype made of weighted styrofoam and then worked the electronic components - display, circuitboard, batteries - into it using 3-D modeling. Priced at less than $500, the Rocket eBook is scheduled to be available in the U.S. in Levenger retail catalogs for the 1998 holiday shopping season.

If you ever do the hardware setup procedure with your computer, you effectively will be writing to ROM.

   Newer computers come with BIOS systems that read the two-digit year date in the real-time clock and convert it into the appropriate four-digit year date. Older PCs with a BIOS that doesn't convert it into the right four-digit year date are likely to cause problems on or, in some cases before, January 1, 2000 - which the BIOS is likely to read as "1900." Computer owners with older PCs may want to upgrade or acquire software that will test for and perhaps provide a programming fix to avoid this particular Year 2000 problem.

   In general, real-time operating systems are said to require:

• Multitasking
• Process threads that can be prioritized
• A sufficient number of interrupt levels

   Real-time operating systems are often required in small embedded operating systems that are packaged as part of microdevices. Some kernels can be considered to meet the requirements of a real-time operating system. However, since other components, such as device drivers, are also usually needed for a particular solution, a real-time operating system is usually larger than just the kernel.

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