Hard Drive Glossary

Hard Drive Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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DATA An ordered collection of information. In a specific case, it is the information processed by a computer. DATA RELIABILITY Average data error rate allowed with all error recovery features activated. DATA SEPARATOR An electronic circuit which decodes playback data and produces separate clock and data bits. Sometimes incorrectly used to denote data synchronizer. DATA SYNCHRONIZER An electronic circuit producing a clock signal that is synchronous with the incoming data stream. This clock signal is then used to decode the recording code being used into user data. DATA TRANSFER RATE In a disk or tape drive, the rate at which data is transferred to or from the storage media. It is usually given in thousands of bits per second (Kbit/second) or millions of bits per second (Mbit/second). See: PIO, DMA or Ultra-DMA for more detail. DEDICATED LANDING ZONE A designated radial zone on the disk where contact starting and stopping occur by design. DEDICATED SERVO A servo scheme in which a prerecorded pattern on an otherwise unused disk surface provides position information to the servo circuitry by means of a head reading that surface. DEFECT A magnetic imperfection in a recording surface. DEFECT MANAGEMENT A general methodology of avoiding data errors on a recording surface by avoiding the use of known bad areas of media. Usually defective sectors or tracks are retired and data are written in alternate locations. Several algorithms are possible such as “sector slipping”, or “spare sector per track”. DEFECT MAP A list of defects that fall within a pass/fail criteria of a user. This list is usually used by an operating system or a disk drive controller for defect management. DEFECT SKIPPING A defect management scheme for avoiding surface defects. It has data written before and after the defect, instead of using alternate tracks or sectors to avoid use of the defective area. DENSITY Generally, recording density. See areal, bit, and storage density. DC ERASE The method of erasing a track using a DC write/erase current through either a Read/Write or Erase head. DIGITAL Any system that processes digital binary signals (having only values of a 1 or 0; usually in bits and bytes) rather than analog signals (signals that can have many values). DIGITAL MAGNETIC RECORDING See magnetic recording. DIGITAL SIGNAL PROCESSOR (DSP) DSP is a technology unique to Maxtor Hard Drives. Maxtor’s Digital Signal Processor (DSP) based electronics design was developed in cooperation with Texas Instruments. This is the industry’s first DSP based architecture to feature a uniprocessor that can interface both with the controller and the drive processor. DIRECT ACCESS Access directly to memory location. (See Random Access Memory). DIRECT MEMORY ACCESS A means of data transfer between the device and host memory without processor intervention. There are two DMA modes, Single and Multi-Word or (PIO Mode). Since single word is slower than PIO mode, it is no longer used and will be not be referred to here. Multi Word DMA is used in EISA, VLB, and PCI equipped systems, which are capable of very fast transfer rates, utilizing cycle times of 480ns or faster. The current ATA specification limit is 150ns. DMA eliminates the CPU from the transfer process. The system specifies where the data transfer is to begin, and how many sectors to transfer. The system sends a Read/Write DMA command to transfer data. The drive asserts DERQ to signify it is ready to transfer data. The DMA controller asserts DACK- to indicate the bus is free to transfer data, and enables the memory address where the data needs to either come from or go to. When IOR- or IOW- are asserted, the drive transmits or receives a word of data. If the next word of data is ready to be transmitted or received, step 5 is repeated. If the data is not ready, the following occurs: The drive negates DREQ and tells the DMA controller to temporarily halt the data transfer. The DMA controller responds by negating DACK- and freeing up the bus to the CPU. Once the drive is ready to proceed, the process returns to step 3. Once the entire data transfer is complete, the drive issues an interrupt to tell the CPU the data is where it belongs. DIRECTORY A listing of files maintained by the disk operation system (DOS) or a data base management system to enable a user to quickly access data files. DISK A flat, circular piece of metal (usually aluminum) or plastic (usually mylar) with a magnetic coating upon which information can be recorded. (As an example, a floppy disk or Winchester drive). DISK DRIVE OR DISK MEMORY DEVICE The total electromechanical storage device (hard disk drive) that contains disks, read/write heads, a head positioning mechanism, drive motor, and electronics. DISK PACK A number of metal disks packaged in a canister for removal from the disk drive (predecessor to Winchester technology). DISK OPERATING SYSTEM (DOS) The software package developed to operate the computer and schedules tasks, allocate computer system resources, controls access to mass storage devices, manage files, etcetera. Typical disk operating systems include CP/M, MS-DOS, Windows and UNIX. DISK STORAGE Auxiliary memory system containing disk drives. DISK TRANSFER RATE The rate that digital data is transferred from one point to another. Expressed in either bits per second or bytes per second. DOUBLE FREQUENCY ENCODING Double Frequency Encoding is another name for FM encoding. This is due to the fact that all possible data combinations will result in only two possible temporal displacements of adjacent data bits, specifically “1F” and “2F”.
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EARLY WINDOW A data window that has been intentionally shifted in time in an early direction. ENHANCED INTEGRATED DEVICE ELECTRONICS (EIDE) This is the popular name for the ATA-2 interface standard, which features a theoretical maximum data transfer rate of about 16MB/sec. In a real world environment, however, performance with devices on this interface are typically maximized at about 10MB/sec. See also IDE or ATA. EMBEDDED SERVO A servo technique used for track following. Position information is prerecorded between data areas in a track so that a data head, and proper additional circuitry, can determine the data head location with respect to the center position of the track (or cylinder) in question. ENERGY STAR EPA Energy Star Compliance: Maxtor Corporation supports the goals of the U.S. Environmental Protection Agency’s Energy Star program to reduce the electrical power consumption of computer equipment. ERASE A process by which a signal recorded on a medium is removed and the medium made ready for rerecording. ERROR CORRECTION CODE (ECC) A mathematical algorithm that can detect and correct errors in a data field. This is accomplished with the aid of Check Bits added to the raw data. ERROR FREE A recording surface that has no defects. ERROR RATE The number of errors, which must be specified, occur in a specified number of bits read. ERROR RECOVERY PROCEDURE The process that occurs in response to a data error. In a drive without ECC, (Error Correcting Code), this would include re-calibration and re-seeking to the specified track and rereading the specified data. Enhanced Small Device Interface (ESDI) An interface standard developed in the early 1980s by a consortium of the leading personal computer manufacturers for connecting disk drives to PCs. ESDI is two to three times faster than the older ST-506 standard. To use an ESDI drive, your computer must have an ESDI controller. ESDI is already obsolete. Instead, modern computers use a SCSI, IDE, EIDE, or Ultra DMA interface. All XT-Series ESDI drives are now owned by Reset Inc.. They are responsible for sales, repair and support of these products. EXECUTE To perform a data processing operation described by an instruction or a program. EXTRA PULSE Term used in surface certification. It is when a flux field discontinuity remains after the recording surface is erased, thereby producing an electrical output of a read head passing over the area with the discontinuity. An extra pulse occurs when the electrical output is larger than a specified threshold.
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FAT 16 One of the first versions of FAT (See File Allocation Table) Technology was FAT 16. FAT 16 features: Supports a Maximum of four volumes of 2 GB each = 8.4 GB Maximum sized Hard Drive. Uses larger clusters (32 KB clusters for drives up to 2 GB in size), which can result in inefficient use for today’s high capacity hard drives. Can be upgraded to FAT 32. FAT 32 A more recent version of FAT (See File Allocation Table) Technology is FAT 32. FAT 32 features: A 2 terabyte maximum size Hard Drive (2,000 GB). Will NOT work with Windows NT 4.0. More efficient use of disk space. FAT 32 uses smaller clusters (e.g. 4 KB clusters for drives up to 8 GB in size), resulting in 10 to 15% more efficient use of disk space relative to large FAT drives. Less susceptible to a single point of failure than existing FAT volumes. Allows for dynamic resizing of FAT 32 partitions on hard drives. More space up to 28% more according to Microsoft over FAT 16. FACTORY RESERVED These are drive jumper positions that are reserved for future options. FEEDBACK In a closed-loop system, the output signal from the servo head is used to modify the input signal to the positioner. FETCH A read operation and its related data transfer operations. FILE ALLOCATION TABLE (FAT) The file allocation table allocates space on the disk for files, one cluster at a time; locks out unusable clusters; identifies unused, or free, area; and lists each files specific location. With two FATs present, the second copy ensures consistency and protects against loss of data if one of the sectors on the first FAT is damaged. Most FATs are 16 bit, Microsoft created a new 32-bit FAT in the OSR2 of Windows 95 and it is present in all versions of Windows 98. FLAW See defect. FLAW MAP See defect map. FLUX When a magnetic field is applied to a particular material, a magnetic flux is induced. The magnitude of this inductance is proportional to the magnetic permeability of the material. FLUX CHANGES PER INCH (CPI) Synonymous with frpi (flux reversals per inch). Only in MFM recording does 1 fci equal 1 bpi (bit per inch). In run-length-limited encoding schemes, generally 1 fci equals 1.5 bpi. FORMAT The preparation of a hard drive for installation and use of an operating system after having been partitioned. In a disk drive, the arrangement of data on a storage media. A standard 5.25-inch disk format consists of 17, 26, or 36 sectors per track, and 512 bytes of data per sector, plus identification, error correction, and other bytes necessary for accessing and synchronizing data. FORMATTED CAPACITY The actual capacity available to store data in a mass storage device. The formatted capacity is the gross capacity, less the capacity taken up by the overhead data used in formatting the sectors. FREQUENCY MODULATION (FM) A recording code. A flux reversal at the beginning of a cell time represents clock bit; a “1” bit is a flux reversal at the center of the cell time, and a “0” bit is an absence of a flux reversal. FREQUENCY RESPONSE A measure of how effectively a circuit or device transmits the different frequencies applied to it. In disk and tape drives this refers to the read/write channel. In disk drives, it can also refer to the dynamic mechanical characteristics of a positioning system.
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GIGABYTE (GB) A confusing term, it can mean either 1,000,000,000 bytes decimal (109) or 1,073,741,824 bytes digital (230). Most drive manufacturers define 1GB as 1,000,000,000 bytes, or One Billion Bytes (one thousand megabytes). See: Decimal vs. Digital for further details. GUI (Graphical User Interface) A GUI interface (your interaction with the computer and its software) is graphical in nature rather than one of plain text. As an example, if you started your computer in MS-DOS, that is a textural format. If, on the other hand, you started your computer and used Microsoft’s Windows, that is a GUI interface. The term came into existence because the first interactive user interfaces to computers were not graphical; they were text-and-keyboard oriented, and usually consisted of commands you had to remember and computer responses that were largely vague to the inexperienced user. The command interface of the DOS operating system is an example of the typical computer interface before graphical user interface arrived. An intermediate step in user interfaces between the command line interface and the GUI was the non-graphical menu-based interface, which let you interact by using a mouse rather than by having to type in keyboard commands. Almost all of today’s major operating systems provide a graphical user interface. Applications typically use the elements of the GUI that come with the operating system and add their own graphical user interface elements and ideas. A GUI sometimes uses one or more metaphors for object familiarity in real life, such as the desktop, the view through a window, or the physical layout of a building. Elements of a GUI include such things as the use of windows, pull-down menus, buttons, scroll bars, icon based images, wizards, the mouse, and will no doubt include many things that haven’t been developed yet. With the increasing use of multimedia as part of this interface, sound, voice, motion video, and virtual reality seem likely to become part of the GUI in the future. The Graphical User Interface most familiar to us today is integrated into either the Mac or the Windows operating systems and their applications, which originated at the Xerox Palo Alto Research Laboratory in the late 1970s. Apple used it in their first Macintosh computers. Later, Microsoft used many of the same ideas in their first version of the Windows operating system for IBM-compatible PCs. When creating an application, many object-oriented tools exist that facilitate writing a graphical user interface. Each GUI element is defined as a class from which you can create object instances for your application. You can code or modify prepackaged methods that an object will use to respond to user stimuli.

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