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Block Availability Map
In computer file systems, a block availability map (BAM) is a data structure used to track block size (data storage and transmission), disk blocks that are considered free (available for new data). It is used along with a directory (file systems), directory to manage files on a disk (originally only a floppy disk, and later also a hard_disk_drive, hard disk). In terms of Commodore DOS (Commodore International, CBM disk operating system, DOS) compatible disk storage, disk drives, the BAM was a data structure stored in a reserved area of the disk (its size and location varied based on the physical characteristics of the disk). For each track, the BAM consisted of a bitmap of available block (data storage), blocks and (usually) a summation, count of the available blocks. The count was held in a single byte, as all formats had 256 or fewer blocks per track (disk drive), track. The count byte was simply the sum of all 1-bits in the bitmap of bytes for the current track. The following ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disk Sector
In computer disk storage, a sector is a subdivision of a track on a magnetic disk or optical disc. For most disks, each sector stores a fixed amount of user-accessible data, traditionally 512 bytes for hard disk drives (HDDs), and 2048 bytes for CD-ROMs, DVD-ROMs and BD-ROMs. Newer HDDs and SSDs use 4096 byte (4 KiB) sectors, which are known as the Advanced Format (AF). The sector is the minimum storage unit of a hard drive. Most disk partitioning schemes are designed to have files occupy an integral number of sectors regardless of the file's actual size. Files that do not fill a whole sector will have the remainder of their last sector filled with zeroes. In practice, operating systems typically operate on blocks of data, which may span multiple sectors. Geometrically, the word sector means a portion of a disk between a center, two radii and a corresponding arc (see Figure 1, item B), which is shaped like a slice of a pie. Thus, the ''disk sector'' (Figure 1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Free Space Bitmap
Free-space bitmaps are one method used to track allocated sectors by some file systems. While the most simplistic design is highly inefficient, advanced or hybrid implementations of free-space bitmaps are used by some modern file systems. Example The simplest form of free-space bitmap is a bit array, i.e. a block of bits. In this example, a zero would indicate a free sector, while a one indicates a sector in use. Each sector would be of fixed size. For explanatory purposes, we will use a 4 GiB hard drive with 4096-byte sectors and assume that the bitmap itself is stored elsewhere. The example disk would require 1,048,576 bits, one for each sector, or 128 KiB. Increasing the size of the drive will proportionately increase the size of the bitmap, while multiplying the sector size will produce a proportionate reduction. When the operating system (OS) needs to write a file, it will scan the bitmap until it finds enough free locations to fit the file. If a 12 K ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Design Of The FAT File System
The FAT file system is a file system used on MS-DOS and Windows 9x family of operating systems. It continues to be used on mobile devices and embedded systems, and thus is a well-suited file system for data exchange between computers and devices of almost any type and age from 1981 through to the present. Structure A FAT file system is composed of four regions: FAT uses little-endian format for all entries in the header (except for, where explicitly mentioned, some entries on Atari ST boot sectors) and the FAT(s). It is possible to allocate more FAT sectors than necessary for the number of clusters. The end of the last sector of each FAT copy can be unused if there are no corresponding clusters. The total number of sectors (as noted in the boot record) can be larger than the number of sectors used by data (clusters × sectors per cluster), FATs (number of FATs × sectors per FAT), the root directory (n/a for FAT32), and hidden sectors including the boot sector: this would ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File Allocation Table
File Allocation Table (FAT) is a file system developed for personal computers and was the default file system for the MS-DOS and Windows 9x operating systems. Originally developed in 1977 for use on floppy disks, it was adapted for use on Hard disk drive, hard disks and other devices. The increase in disk drive capacity over time drove modifications to the design that resulted in versions: #FAT12, FAT12, #FAT16, FAT16, #FAT32, FAT32, and exFAT. FAT was replaced with NTFS as the default file system on Microsoft operating systems starting with Windows XP. Nevertheless, FAT continues to be commonly used on relatively small capacity solid-state storage technologies such as SD card, MultiMediaCard (MMC) and eMMC because of its compatibility and ease of implementation. Uses Historical FAT was used on hard disk drive, hard disks throughout the DOS and Windows 9x eras. Microsoft introduced NTFS with the Windows NT platform in 1993, but FAT remained the standard for the home use ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CMD HD Series
CMD may refer to: Entities * Cable Mágico Deportes, a Peruvian TV network * Center for Media and Democracy, advocacy organization in the US * Center for Molecular Design, Janssen Pharmaceutica * Coleg Meirion-Dwyfor, a college in Gwynedd, Wales * Creative Micro Designs, a defunct American computer peripheral company * CMD Technology, a defunct American computer storage controller company * Lakas–CMD, Lakas–Christian Muslim Democrats, a political party in the Philippines Medical * Congenital muscular dystrophy * Craniomandibular dysfunction * Custom-made device, a medical device designed and manufactured for the specific use of a particular patient. Technology * cmd.exe, command prompt on the OS/2 and Windows NT families of operating systems * CMD file (CP/M), the filename extension used by executable programs * Command key, usually abbreviated "cmd" * Concerted metalation deprotonation, a kind of chemical reaction Travel * Camden Road railway station, L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CMD FD Series
The CMD FD series was Creative Micro Designs (CMD)'s range of third-party floppy disk drives for the Commodore International, Commodore 8-bit line of home computers. Using 3½" floppy disks, they provided a significantly larger storage capacity than Commodore-produced drives; the FD-2000 offered 1600 Kilobyte, kB of storage using standard double-sided, high-density floppies, while the FD-4000 also allowed the use of 3200 kB extra-high density (ED) floppies. In contrast, the Commodore 1581 3½" drive only supported 800 kB double-sided, double-density disks. Features In addition to the higher storage capacity, the FD series also provided additional features not found on the Commodore 1581. A "SWAP" button on the front panel allowed the drive number to be easily switched with that of another Commodore drive on the serial bus, without the need to enter any commands into the computer. It also provided a "1541 emulation mode", allowing partitions on a 3½" disk to simulate the behavior o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Creative Micro Designs
Creative Micro Designs, Inc. (CMD) was founded in 1987 by Doug Cotton and Mark Fellows. It is a computer technology company which originally developed and sold products for the Commodore 64 and C128 8-bit personal computers. After 2001 it sold PCs and related equipment. History CMD's first product, JiffyDOS, was developed from 1985 onwards by Mark Fellows. An updated disk operating system, it maintained broad compatibility with Commodore floppy drives' DOS while offering much increased read-write access. CMD stopped selling Commodore products in 2001. In July of that year, programmer Maurice Randal was sold an exclusive license to produce and sell the Commodore-related products. His company Click Here Software Co supplied the products until around 2009. In 2010, Jim Brain acquired the license to supply JiffyDOS. Since January of that year, he has sold the product via his webshop Retro Innovations. Products * SuperCPU - A 65816 CPU 8/16-bit upgrade for the C64 and C128 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Most Significant Bit
In computing, bit numbering is the convention used to identify the bit positions in a binary numeral system, binary number. Bit significance and indexing In computing, the least significant bit (LSb) is the bit position in a Binary numeral system, binary Integer (computer science), integer representing the lowest-order place of the integer. Similarly, the most significant bit (MSb) represents the highest-order place of the binary integer. The LSb is sometimes referred to as the ''low-order bit''. Due to the convention in positional notation of writing less significant digits further to the right, the LSb also might be referred to as the ''right-most bit''. The MSb is similarly referred to as the ''high-order bit'' or ''left-most bit''. In both cases, the LSb and MSb correlate directly to the least significant Numerical digit, digit and most significant digit of a decimal integer. Bit indexing correlates to the positional notation of the value in base 2. For this reason, bit in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Least Significant Bit
In computing, bit numbering is the convention used to identify the bit positions in a binary number. Bit significance and indexing In computing, the least significant bit (LSb) is the bit position in a binary integer representing the lowest-order place of the integer. Similarly, the most significant bit (MSb) represents the highest-order place of the binary integer. The LSb is sometimes referred to as the ''low-order bit''. Due to the convention in positional notation of writing less significant digits further to the right, the LSb also might be referred to as the ''right-most bit''. The MSb is similarly referred to as the ''high-order bit'' or ''left-most bit''. In both cases, the LSb and MSb correlate directly to the least significant digit and most significant digit of a decimal integer. Bit indexing correlates to the positional notation of the value in base 2. For this reason, bit index is not affected by how the value is stored on the device, such as the value's byte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit of memory in many computer architectures. To disambiguate arbitrarily sized bytes from the common 8-bit definition, network protocol documents such as the Internet Protocol () refer to an 8-bit byte as an octet. Those bits in an octet are usually counted with numbering from 0 to 7 or 7 to 0 depending on the bit endianness. The size of the byte has historically been hardware-dependent and no definitive standards existed that mandated the size. Sizes from 1 to 48 bits have been used. The six-bit character code was an often-used implementation in early encoding systems, and computers using six-bit and nine-bit bytes were common in the 1960s. These systems often had memory words of 12, 18, 24, 30, 36, 48, or 60 bits, corresponding t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Little Endian
'' Jonathan_Swift.html" ;"title="Gulliver's Travels'' by Jonathan Swift">Gulliver's Travels'' by Jonathan Swift, the novel from which the term was coined In computing, endianness is the order in which bytes within a word (data type), word of digital data are transmitted over a data communication medium or Memory_address, addressed (by rising addresses) in computer memory, counting only byte significance compared to earliness. Endianness is primarily expressed as big-endian (BE) or little-endian (LE), terms introduced by Danny Cohen into computer science for data ordering in an Internet Experiment Note published in 1980. Also published at The adjective ''endian'' has its origin in the writings of 18th century Anglo-Irish writer Jonathan Swift. In the 1726 novel ''Gulliver's Travels'', he portrays the conflict between sects of Lilliputians divided into those breaking the shell of a boiled egg from the big end or from the little end. By analogy, a CPU may read a digital word bi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
