Qué (quién) es Head Disk Assembly - definición

HISTORICAL METHOD FOR GIVING ADDRESSES TO PHYSICAL DATA BLOCKS ON HARD DISK DRIVES

Cylinder-Head-Sector; Cylinder (disk drive); Disk drive cylinder; Cylinder Head Sector; Disk Cylinder; Disk cylinder; C/H/S

Head Disk Assembly

<hardware, storage> (HDA) A sealed, high capacity mainframe hard disk with integral heads, as opposed to a {removable disk}. (1999-01-13)

disk drive

STORAGE MECHANISMS THAT RECORD DATA ON THE SURFACE OF ROTATING DISKS

Disk drive; Computer disk; Disk Drive; Disc storage; Disc drive; Disk memory; Disc Drive; Disk (storage device); Rotating-disk memory; Data storage disk; Computer disc

<hardware, storage> (Or "hard disk drive", "hard drive", "floppy disk drive", "floppy drive") A peripheral device that reads and writes hard disks or floppy disks. The drive contains a motor to rotate the disk at a constant rate and one or more read/write heads which are positioned over the desired track by a servo mechanism. It also contains the electronics to amplify the signals from the heads to normal digital logic levels and vice versa. In order for a disk drive to start to read or write a given location a read/write head must be positioned radially over the right track and rotationally over the start of the right sector. Radial motion is known as "seeking" and it is this which causes most of the intermittent noise heard during disk activity. There is usually one head for each disk surface and all heads move together. The set of locations which are accessible with the heads in a given radial position are known as a "cylinder". The "seek time" is the time taken to seek to a different cylinder. The disk is constantly rotating (except for some floppy disk drives where the motor is switched off between accesses to reduce wear and power consumption) so positioning the heads over the right sector is simply a matter of waiting until it arrives under the head. With a single set of heads this "rotational latency" will be on average half a revolution but some big drives have multiple sets of heads spaced at equal angles around the disk. If seeking and rotation are independent, access time is seek time + rotational latency. When accessing multiple tracks sequentially, data is sometimes arranged so that by the time the seek from one track to the next has finished, the disk has rotated just enough to begin accessing the next track. See also sector interleave. The disks may be removable disks; floppy disks always are, removable hard disks were common on mainframes and minicomputers but less so on microcomputers until the mid 1990s(?) with products like the Zip Drive. A CD-ROM drive is not usually referred to as a disk drive. Two common interfaces for disk drives (and other devices) are SCSI and IDE. ST-506 used to be common in microcomputers (in the 1980s?). (1997-04-15)

disk drive

STORAGE MECHANISMS THAT RECORD DATA ON THE SURFACE OF ROTATING DISKS

Disk drive; Computer disk; Disk Drive; Disc storage; Disc drive; Disk memory; Disc Drive; Disk (storage device); Rotating-disk memory; Data storage disk; Computer disc

¦ noun a device which allows a computer to read from and write on to computer disks.

Wikipedia

Cylinder-head-sector

Cylinder-head-sector (CHS) is an early method for giving addresses to each physical block of data on a hard disk drive.

It is a 3D-coordinate system made out of a vertical coordinate head, a horizontal (or radial) coordinate cylinder, and an angular coordinate sector. Head selects a circular surface: a platter in the disk (and one of its two sides). Cylinder is a cylindrical intersection through the stack of platters in a disk, centered around the disk's spindle. Combined, cylinder and head intersect to a circular line, or more precisely: a circular strip of physical data blocks called track. Sector finally selects which data block in this track is to be addressed, as the track is subdivided into several equally-sized portions, each of which is an arc of (360/n) degrees, where n is the number of sectors in the track.

CHS addresses were exposed, instead of simple linear addresses (going from 0 to the total block count on disk - 1), because early hard drives didn't come with an embedded disk controller, that would hide the physical layout. A separate generic controller card was used, so that the operating system had to know the exact physical "geometry" of the specific drive attached to the controller, to correctly address data blocks. The traditional limits were 512 bytes/sector × 63 sectors/track × 255 heads (tracks/cylinder) × 1024 cylinders, resulting in a limit of 8032.5 MiB for the total capacity of a disk.

As the geometry became more complicated (for example, with the introduction of zone bit recording) and drive sizes grew over time, the CHS addressing method became restrictive. Since the late 1980s, hard drives began shipping with an embedded disk controller that had good knowledge of the physical geometry; they would however report a false geometry to the computer, e.g., a larger number of heads than actually present, to gain more addressable space. These logical CHS values would be translated by the controller, thus CHS addressing no longer corresponded to any physical attributes of the drive.

By the mid 1990s, hard drive interfaces replaced the CHS scheme with logical block addressing (LBA), but many tools for manipulating the master boot record (MBR) partition table still aligned partitions to cylinder boundaries; thus, artifacts of CHS addressing were still seen in partitioning software by the late 2000s.

In the early 2010s, the disk size limitations imposed by MBR became problematic and the GUID Partition Table (GPT) was designed as a replacement; modern computers using UEFI firmware without MBR support no longer use any notions from CHS addressing.

https://en.wikipedia.org/wiki/Cylinder-head-sector