Non removable disk geometry

under geometry of a non removable disk one understands the allocation of the non removable disk in cylinders, heads and sectors.

The data on non removable disks (and also disks) are divided into small „Häppchen “- so-called data blocks -, which have a constant size of (usually 512 bytes). In addition the sides of all disks of a non removable disk are durchnummeriert. (A disk has naturally maximum two sides - front and back). Each side has its own write/read head, therefore one speaks of the number of heads. The circular surfaces again are divided into sectors and concentric traces. The respective traces of all disk surfaces of the disk pack are summarized as so-called cylinders.

If one wants so, from it a kind coordinate system, with its assistance one to each data block by its head, results cylinder and sector number to identify can. The head number corresponds thereby the height, the cylinder number the radius and the sector number the angle of an object in a cylindrical coordinate system.

Since the traces with rising radius become also accordingly longer, they become if necessary. accordingly into more blocks divides. (Thus the recording density of the traces becomes angegelichen - and thus „more wasted “place on the outside traces avoided.) with disks this procedure is nowadays rather uncommon.

In order to let the administration of the data blocks become too complex, become usually several neighbouring traces into zones combined. Each zone is partitioned into a certain number of sectors, which falls from zone to zone. (Normally one begins the counting of the cylinders and/or. Zones at the outside edge.)

the concrete distribution of the blocks on the surfaces, zones, cylinders and sectors becomes as geometry of the non removable disk (and/or. Disk) marks.

In order to address now a physical data block, one needs three values (also CHS - values called; of C more ylinder, H ead (head) and S ector).

Over restrictions by BIOS and/or. Operating systems (missing or insufficient support of zones as well as the administration of defective blocks, restrictions of the maximum number of cylinders, heads or traces) to go around to be able, with practically all non removable disks (logical) geometry visible of the operating system is converted by its CONTROLLER into internal (physical) geometry.

In logical consequence nowadays CHS addresses become i. A. no more does not use, but the data blocks are sequentially durchnummeriert and addressed over their block number (LBA - procedures). Thus the operating system no more does not have to worry about the physical organization of the blocks on the data medium. Since many non removable disks support both addressing procedures, the illustration of the CHS address is standardized on the appropriate LBAdresse, so that a change of the addressing procedure does not force to the new formatting.

 

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