Direct access storage device (DASD)

A temporary storage area, usually in RAM. The purpose of most buffers is to act as a holding area, enabling the CPU to manipulate data before transferring it to a device. Because the processes of reading and writing data to a disk are relatively slow, many programs keep track of data changes in a buffer and then copy the buffer to a disk. For example, word processors employ a buffer to keep track of changes to files. Then when you save the file, the word processor updates the disk file with the contents of the buffer. This is much more efficient than accessing the file on the disk each time you make a change to the file. Note that because your changes are initially stored in a buffer, not on the disk, all of them will be lost if the computer fails during an editing session. For this reason, it is a good idea to save your file periodically. Most word processors automatically save files at regular intervals. Another common use of buffers is for printing documents. When you enter a PRINT command, the operating system copies your document to a print buffer (a free area in memory or on a disk) from which the printer can draw characters at its own pace. This frees the computer to perform other tasks while the printer is running in the background. Print buffering is called spooling. Most keyboard drivers also contain a buffer so that you can edit typing mistakes before sending your command to a program. Many operating systems, including DOS, also use a disk buffer to temporarily hold data that they have read from a disk. The disk buffer is really a cache.
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Punched or magnetic tape containing key. Printed key in tape form is referred to as a key list.
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An Internet protocol used to run IP over serial lines such as telephone circuits or RS232 cables interconnecting two systems. SLIP is now being replaced by PointtoPoint Protocol. See PointtoPoint Protocol. An older technology developed to support TCP/IP communications over asynchronous serial connections, such as serial cables or modem dial- up.
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Disk mirroring protects data against hardware failure. In its simplest form, a twodisk subsystem would be attached to a host controller. One disk serves as the mirror image of the other. When data is written to it, it is also written to the other disk. Both disks will contain exactly the same information. If one fails, the other can supply the user data without problem.
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A magnetic tape technology. DAT uses 4mm cassettes capable of backing up anywhere between 26 and 126 bytes of information.
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