Non removable disk

Storage medium
geöffnete Festplatte: drei Magnetscheiben, Lesekopf, Mechanik
general
name hard disk drive
abbreviation HDD
type magnetically
origin
invention year of 1956
inventors IBM
data
size 3.5 ″
weight approx. 0.6 kg
of number of revolutions up to 15.000 min −1
storage capacity up to 750 GB (conditions: 04.2006)
Buffer size up to 16MT
fastest data transmission rate approx. For 100 MB/s (server non removable disks)
minimum operating temperature (type.) 5 °C
maximum operating temperature (type.) 60 °C
life span several years (hangs from many factors)
the range „data “applies only to 3,5 ″ - non removable disks and can dependent on the concrete model vary
write/read heada non removable disk
commercial 3.5 ″ - non removable disk (Western digitally WD400) from above (left) and from downside (right)

a non removable disk (English. hard disk (hp) or hard disk drive (HDD)) is a magnetic storage medium of the computer engineering. The magnetic stratum is on rigid, round, rotary platesapplied, this contrary to the disk, which consists of a flexible material.

The first commercially available non removable disk, IBM 350, was announced by IBM 1956. 1973 started likewise IBM „the Winchester “- project, which the first drive assembly with a sealed unitfrom plates, access mechanics and write/read heads (IBM 3340) brought out. This technology became generally accepted in the following years and into the 1990er years was therefore for non removable disks the name Winchester drive assembly common.

On a non removable disk arbitrary files can,for example the operating system, by application programs, or personal data (documents, video, music, pictures) durably to be stored.

Table of contents

general one technical data

storage capacity

the capacity of a non removable disk is usually indicated today in gigabyte (GB).

Above all non removable disk manufacturers define a gigabyte with the indication of the capacity as 1000 3   byte = 10 9   byte = 1.000.000.000   byte, while computer programs a gigabyteusually as 1024 30   byte = 1.073.741.824 byte treat 3   byte = 2. With the binary prefixes (Mebibyte, Gibibyte) one tries to avoid this ambiguity.

If one the capacity of a non removable disk, those in „gigabyte “(1000 3   byte = 109 one indicated   to byte), into Gibibyte (give, 1024 3   byte = 2 30   byte) to convert would like, then one can use the following conversion factor: <math> \ frac {1000^3} {1024^3} =0 {,} 93132 \ frac {\ mathrm {give}} {\ mathrm {to GB}}< /math>

Example: <math> 80 \ \ mathrm {GB} \ 0 {,} 93132 \ \ frac {\ mathrm {gives}} {\ mathrm {GB cdot}} = 74 {,} 51 \ \ mathrm {gives}< /math>

Many computer programs show the capacityin units with binary prefix (z. B. Gibibyte) on, often however falsely with decimal prefix (like gigabyte) marks.

Beginning of 2005 non removable disks to 400 GB (372.53 give ) were available capacity. In June 2005 it already gave a non removable disk from HitachiTo buy 500 GB capacity for final customers.

physical dimension of non removable disks traditionally in tariff

and is no accurate statement of size, but a crest factor is indicated to sizes 1 GByte IBM MicroDrive (1 ″ ). So are accurate for example 3.5 ″ - non removable disks100 mm wide, which corresponds scarcely to 4 tariff. The size of the disks in this 100 mm broad housings lies however around the 3.5 tariff, whereby server plates are frequently somewhat smaller.

The crest factors used at present are enough from 5,25 ″ to 0.85 ″,whereby the trend goes to smaller non removable disks. The 3.5 ″ - crest factor is in the Desktop range of the furthest common, in laptops finds one usually 2.5 ″ - non removable disks, in still smaller portable devices (z. B.MP3-Player) frequently 1.8 ″ - non removable disks.

  • The first non removable disks had sizes of 24 "(IBM 350, 1956). In the course of the time these sizes were reduced.
  • 5,25 ″ - sizes are the 1980 of Seagate introduced sizes of the PC non removable disks, however this kind became extinct however since 1996/97. Some SCSI server plates, as well as the LowCost IDE plate BigFoot of quantity were the latterRepresentative of this species. One differentiates between devices with full overall height (3.5 ″ and/or. approx. 88 mm), the two card locations occupy and half overall height (1.75 ″ and/or. approx. 44 mm). The width amounts to 146 mm, the depth is variable and should not not substantially upfrom 200 mm lie.
  • 3,5 ″ - sizes became over approx. 1990 imported and presently in Desktop computers and servers, most plates are used to have half overall height (1 ″ and/or. approx. 25 mm). Within the server range there is also plates to 1.8 ″ height (1.8 ″ and/or.approx. 44 mm). The width amounts to 100 mm, the depth is variable and should not substantially above 150 mm lie.
  • 2,5 ″ - sizes find use in Notebooks or special-purpose computers. The traditional overall height was 0.5 ″ (12.7 mm), meanwhile gives it with 0,375 ″(9.5 mm) and 0.25 ″ (6.35 mm) flatter non removable disks and also Notebooks, which need these flat variants. The width amounts to 68 mm, the depth amounts to 100 mm. The connection is modified in relation to the larger designs, with IDE e.g. becomes. a 44-poligerConnection uses, which at the same time supplies the operating voltage of +5 V (pin 1 is usually on the side of the Jumper). Contrary to the larger plates these plates get along also with only an operating voltage.
  • 1,8 ″ - sizes become since 2003 with Sub Notebooksas well as 1 uses various
  • industrial's applications ″ - sizes are since 2002 under name the MicroDrives in use. Most MicroDrives begun to in the middle of 2004 as „disguised CompactFlash - type ii-memory units for digital cameras. Hauptnachteil is mechanical sensitivity outside from devices and the highCurrent consumption.
  • 0,85 ″ - sizes are at present (January 2005) only in limited quantities over the company Toshiba available, who presented this size in March 2004 with a capacity of 4 gigabyte (3.73 give) for the first time. Whether these small designs ever existencewill have, is questionable.Flash memory is already available in this range and on growth course. Presently Flash memory is still more expensive, but substantially more durable and more economically in the energy consumption.


overview of the storage capacities of the different sizes

Year 5.25 ″ 3.5 ″ 2,5 ″ 1,8 ″ 1.0 ″ 0.85 ″ type. Model (e) with high capacity source
1983 20 MByte - - - - - 20 MT non removable disk in IBM the PC XT
1989 80 MByte 40 MT - - - - Seagate ST4096, NEC D3142
1995 4096 MByte 850 MByte - - - - Western digital with 850 MT
1997 12 GByte 9 GByte 2 GByte - - - quantity Bigfoot (12 GB, 5.25 ″), Nov. 1997 [1]
2000 # >75 GByte? ? GByte - - - ?
2005 # 500 GByte 120 GByte 60 GByte 8 GByte 6 GByte Hitachi Deskstar 7K500 (500 GB, 3.5 ″), July 2005 [2]
2006 # 750 GByte * 160 GByte * 60 GByte 8 GByte 6 GByte Western digitally WD5000KS, Seagate Barracuda7200,9 500GB, among other things [3]

Notes:

  • Data refer always to to the respective year the largest available available non removable disk, independently of its number of revolutions or interface.
  • Capacities are manufacturer data, D. h. a gigabyte is defined as <math> 1000^3 byte = 10^9 byte =1.000.000.000 byte< /math>, a megabyte as <math> 1000^2 byte = 10^6 byte< /math>
  • With question marks marked entries please verify/supplement
  • - not yet available
  • * using perpendicular recording
  • # size becomes outdated; no more in use

structure and function

Skizze einer Festplatte
sketcha non removable disk
of individual parts of a non removable disk

physical structure

consists a non removable disk of the following elements:

non removable disks, which in personal computers or in PCs forthe private use to be used - momentarily mostly plates with ATA or SATA interface - rotate with speeds of 5.400 to 10,000 revolutions per minute. Before the time of the ATA non removable disks and within the range of the high-performance computers and servers becameand/or. mostly become non removable disks with the technically superior SCSI - interface uses, which reach in the meantime usually 10,000 or 15,000 revolutions per minute. With the 2,5-Zoll-Festplatten, which are used mainly into Notebooks, the speeds are within the range of 4.200to 7,200 revolutions per minute.

In the non removable disk housing are one or more rotary disks lying one above the other. Blocked is so far 1 to 12 disks, usually is 1 to 4. However a higher number of disks usually goes with onehigher energy consumption and a larger noise. Sometimes from space reasons not all disk surfaces are used, so that non removable disks with odd number of write/read heads develop. In order to satisfy the demand for non removable disk models with smaller capacity, the manufacturers know likewise in this way the capacitylimit artificially.

If the disks of earlier non removable disks (until 2000) were running in ball bearings, then today (2005) predominant liquid camps (English become. „fluid dynamic bearing “- FDB) uses. These are characterised by a higher life span and a smaller noise.

The disks exist mostly out Aluminum or alloys. They must be form stable, a small electrical conductivity reduce eddy currents.

Into older Desktopfestplatten of IBM (Deskstar 75GXP/40GV DTLA-30xxxx, Deskstar 60GXP/120GXP IC35Lxxxx) from the years 2000 to 2002 glass was used. Newer modelsthe non removable disk section of IBM (2003 taken over by Hitachi) use however again aluminum, with exception of the non removable disks for the server range.

Since these materials themselves possess however no magnetic characteristics, an ferric oxide or a cobalt layer is laid on by approximately a micrometer strength.This is encased additionally by a sleeve from graphite, in order to avoid mechanical damages.

The write/read heads float by by the rotation of the plates a produced air cushion over the disk surface. The flight altitude lies however nowadays (2005) only within the range of nanometers, so that air may not contain any impurities within the non removable disk housing. The production of non removable disks takes place therefore as from semiconductors in pure areas. If a non removable disk in more normal, is opened for contaminated air then already smallest dust/smoke particles, finger marks, etc. provide forprobably irreparable damages of the disk surface and the write/read heads.

For the protection of the surfaces used for data from putting the write/read heads on these, before when switching the non removable disks off the rotational speed was noticeably reduced, drive into the so-called „landing zone “(„landing zone “), in which they are fixed. This park position can be outside of the disks or in the internal area of the plates. The adjustment e.g. happens. over a small magnet, which holds the read head. Traditionally non removable disks had explicitly before switching off byInstruction by the operating system to be parked.

Ventilation hole

parking increases also the impact resistance of the non removable disks for a transport or a change. With modern laptops an acceleration sensor ensures for parking the non removable disk still during a possible free case, all the the damageto limit with the fall of a computer.

The housing of the non removable disk is dust proof, but not hermetically finally: by a small opening with a filter air can penetrate or withdraw. This opening may not be locked usually. There the air pressurein the housing with increasing height over the sea level, for the enterprise however a minimum pressure decreases is, may non removable disks necessary only up to a certain, maximum height be operated. This is usually noted in the associated data sheet.

memoryand vintages from data

storing the data on a non removable disk takes place via the purposeful magnetization of smallest surfaces of a layer of ferrousmagnetic material, which take the value 0 or 1 according to their polarity. The write/read head (solenoid actuator), in principletiny electromagnet, polarizes the individual sectors differently and stores so the data permanently.

Before the letter of the data these become in special procedures like in former times usual procedures GCR, MFM, RLL and today usually with PRML or EPRML codes. A logical bit does not stand therefore any longer physically than magnetized or did not magnetize unit on the disk surface. Also a compression is reached by the recording modes, so that the data density rises.

Both during the writing and during the readingread head of the plate must to be moved and afterwards been waiting before the access to a certain block writes/, until by the rotation of the plate the block under the head is led past. These mechanically caused delays are nowadays with approx. 5-10 ms,which after yardsticks of other computer hardware a small eternity is. From it results the extremely high latency of non removable disks in the comparison with RAM, which must be considered still on the level of the software development and the Algorithmik. Around a high Performanzto reach, a non removable disk must always large quantities of data as far as possible in sequential blocks read or write, because thereby write/read head again to be positioned does not have. One reaches this, by accomplishing as much as possible operations in the RAMand on the plate the positioning of the data on the access samples co-ordinates.

The selection of the data became to approx. 1994 by induction of the magnetic field of the magnetized surface in the coil of the write/read head reach. Over the years however the surfaces became,on those individual bits to be stored, ever smaller - the data density was increased.

In order to pick these data out, smaller and more sensitive read heads are needed. These were developed after 1994: MR - Read heads as well as some years of late GMR - read heads (Riesenmagnetowiderstand). ThatGMR read head is an application of the Spintronik.

Additionally the increase of the data density was reached by better substrate as well as by the optimization of the recording modes.

A newer development (since 2004) is the Perpendicular Recording, that at present and. A. of Toshiba and Hitachi is developed, in order to increase the data density further.

In order to reduce the volume of the drive assemblies with the access to data, the most IDE and SATA non removable disks, which are meant for the the acct agony set, support „AUTOMATIC Acoustics management “(AAM). Becomesthe non removable disk in a quiet mode claimant, the writing and read heads are less strongly accelerated, so that the accesses are quieter. The Laufgeräusch of the disk pack is not changed of it, equally the continuous transfer rate remains unaffected by AAM; however the access time extends.

Read head of a non removable disk in the close-up

logical structure

the magnetic layer of the disks is the actual carrier of the information. It is magnetically impressed on cylindrical traces, while the disk rotates. A disk contains typically some thousand of suchTraces, usually also on both sides. One calls the whole of all identical traces of the individual plates (surfaces) cylinders. Each trace is divided into small logical units, which one calls blocks. A typical block contains 512 byte at information. Each block ordersover control information (check totals), by which it is guaranteed that the information was also correctly written or read. One calls the whole of all blocks, which have the same angle coordinates on the plates, sector. Unfortunately the term becomes sector frequentlyfalsely also synonymously for block uses.

With modern non removable disks is it normally like that that true geometry, thus the number of sectors, heads and cylinders, which are administered by the CONTROLLER integrated in the non removable disk housing (in the following „non removable disk intelligence “mentioned), outwardis no longer visible. The computer, which uses the non removable disk, works then with a virtual non removable disk, which exhibits completely different geometry data. This explains, why e.g. a non removable disk, which exhibits material only four heads, is seen by the computer with 255 heads.A reason for such a virtual concept is that one wanted to overcome delimitations of PC-compatible hardware. Further non removable disk intelligence can fade out defective blocks by this virtual concept, in order to then fade in a block from a reserve trace. For the computer it seesalways so out, as if all blocks would be defective-free and usable. It is assumed that meant reserve traces approx. 10-20% of the storage location indicated on the non removable disk constitute. This storage location can be used by special firmware - versions, which logical-proves then however the life spanthe non removable disk (and/or. data security) to reduce can. Today usual non removable disks divide further the plates in zones, whereby a zone contains several traces with same in each case number of blocks. Further zones can possess another number of blocks per trace.

From view of the operating system non removable disks can be divided by partitions into several ranges. One can understand oneself these as logical non removable disks, those by the non removable disk driver the operating system (and thus possibly. the user) opposite as separate devices to be represented. It is in the behavior (refrained from temporal effects) not recognizably whether it concerns a physically separated non removable disk actually in each case or only around a logical drive assembly on a common non removable disk.

Each partition is usually formatted by the operating system with a file system.Perhaps, depending upon file system used, several blocks are combined into Clustern, which are then the smallest logical unit for data, which are written on the plate. The file system ensures for the fact that data in the form of files on the plateto be put down can. A table of contents in the file system ensures for the fact that files are again found and hierarchically organized to be put down to be able. With MS-DOS and Windows 9x the file Allocation Table was the usual file system.

interfaces

as interface thatNon removable disk to other computer components lately mainly the parallel become interfaces ATA (IDE, OATHS) (predominantly with personnel computers) or SCSI (with servers, workstations and personnel with high order computers) used.

With increasing transmission rate arise heretechnical difficulties, which set an upper border for the data transmission rate (max. 320 MByte/s with SCSI) and the expenditure with the realization increase. Therefore for some years a transition is aimed at to serial interfaces.

First spread serial interfaces forNon removable disks were SSA (Serial STORAGE Architecture, developed by IBM) and have a temperature Channel in the variant FC-AL (have a temperature to Channel Arbitrated loop). SSA non removable disks will today practically no more not manufactured, but have a temperature to Channel non removable disks to become further built for the employment in large memory systems. Have despite their nameit no optical, but an electrical interface.

Since 2002 the new procedure Serial ATA (S-ATA or SATA) at meaning wins. The advantages over ATA (to the demarcation now P-ATA or PATA increases mentioned) are the higher possible information flow-rate and the simplerWiring.2005 was introduced first non removable disks with Serial Attached SCSI (SAS) as potential successors of SCSI for the server and STORAGE range, over two connections can take place data exchange here theoretically with up to 600 MByte/s.

Particularly with SCSI plates andeven with newer S-ATA non removable disks so-called queues (queues) are used. These line the inquiries up to the data medium into a list and sort them according to the physical position on the disk, all as much as possible data with as few a revolutions as possible tooread. The non removable disk-own Cache plays here a large role, since the queues are put down in this (see also: Tagged COMMAND Queuing, native COMMANDs Queuing).

Also universal interfaces become such as FireWire or USB for the connection of external non removable disksused, here however the inserted non removable disks themselves are equipped, the signals by their own electronics for the interface led outward are converted with conventional (usually ATA or S-SATA) interfaces.

Communication via have a temperature Channel - interface, is still more efficient and inthe glass fiber-based form particularly for the use in memory networks (STORAGE AREA network, SAN) conceives. Since the non removable disks are not addressed directly here likewise, but over a CONTROLLER, all kinds can be used by non removable disk interfaces, by FC-AL over SCSI up to Serial ATA. A competitive beginning pursues iSCSI, however using IP - nets.

data security

loss risks and life span

to the typical loss risks belong:

  • Susceptibility from non removable disks particularly is with the new predominantly to attribute very fast turning systems to thermal problems.
  • When mechanical putting the read-write head (Head Crash on) the non removable disk can be damaged. The head floats in the enterprise over the plate and becomes by an air cushion, throughfrom the turning disk drug along air develops, prevented from putting on. With current enterprise the computer should not be moved therefore if possible or been suspended vibrations.
  • Outside magnetic fields can destroy the sectoring of the non removable disk irreversibly. A deletion with a magnetic alternating fieldmakes useless newer non removable disks. This effect goes also from static magnetic fields (e.g. of permanent magnets) out, if they affect the rotary non removable disk.
  • Errors in control electronics or general wear lead to losses.

The average number of operation hours, before oneNon removable disk precipitates, with irreparable plates as MTTF (Mean Time ton of failures) is designated. For non removable disks, which can be repaired, a MTBF is indicated - value (Mean Time Between failure).

The life span of a non removable disk cannot be predicted concretely, because this hangsfrom many factors:

  • a good cooling increases the statistic life span, since mechanics and electronics age less fast and are stressed.
  • Number of accesses (read head movements): By frequent accesses the mechanics wear faster, as if the plate is not used andonly the disk pack turns.
  • Vibrations and impacts: Strong vibrations can to a premature (camp) wear lead and should therefore be avoided.
  • Differences between different model rows of a manufacturer: On the respective model certain series can dependent be constituted, as particularlyapply reliably or error-prone. In order to be able to give statistically exactly data the reliability, are however a large number of identically constructed plates necessary, which are operated under similar conditions. System administrators, which care for many systems, can so in the course of the yearsquite some experiences collect, which non removable disks are inclined rather to remarkable behavior and thus premature loss.

Generally fast-turning server non removable disks are appropriate for a higher MTTF than typical Desktop non removable disks, so that they suggest a higher life span theoretically. Continuous operation and frequent accesses can however to the fact it leads that this relate itself and the non removable disks must be exchanged after few years.

Notebook non removable disks are stressed by the frequent transportation particularly and are accordingly specified despite robusterer design with a smaller MTTF than Desktop non removable disks.

Preventing measures

as preventing measures against overrun are seized therefore the frequently following measures:

  • From important data a backup copy ( Backup ) on another data medium should always exist.
  • Systems, those to be compellingly high available do not have and with those a non removable disk errorOperating interrupt to cause may, mostly has a RAID. A configuration e.g. is. the Mirrorset (RAID 1), with that the data on two non removable disks to be reflected and thus the reliability increases. More efficient configurations are [[RAID#RAID 5: Performance+ parity|RAID 5]] and more highly. A Stripeset (RAID 0) from two non removable disks increased the speed, doubles however the loss risk. RAID 0 is therefore no meaningful measure, in order to prevent overrun.
  • ATA non removable disks order since introduction of ATA-3 in the year 1996 over S.M.A.R.T., an internal monitoring of the non removable disk on reliability. The status can be queried from the outside. A disadvantage is that S.M.A.R.T. no standard is. Each manufacturer defines its error tolerance, i.e. S.M.A.R.T. is only as generalTo regard arranging means. In addition there are non removable disks, whose S.M.A.R.T. Functionality yet before problems does not warn if these became apparent by no longer readable blocks already in the enterprise. One should not itself thus on S.M.A.R.T. left.
  • Over throughOverheating of the non removable disk of conditioned losses to prevent, must be cooled these according to its maximally permitted operating temperature. In servers to it provided quick change picture frames are used and baking plan with exhausts.

data security

target a file to be deleted, becomes usually onlyin the file system it notes that the appropriate data area is free now. The data remain however physically on the non removable disk, until the appropriate range with new data is overwritten. With data rescue programs deleted data can be often at least partially restored therefore.

Also when the Partitionieren or usual formatting the data area, but only the partition table or the description structure of the file system is not overwritten. In the case of a Low level formatting against it the entire addressable range of a non removable disk is overwritten.

Around a safe deletion from sensitive data toguarantee, offer different manufacturers software, which overwrites the data area with the deletion. Mostly can be fallen back however to (nearly) arbitrary and free Unix - distribution, as for example Knoppix or FreeSBIE, which practical-proves directly by CD be started can.The moreover there is different open SOURCE - programs, which likewise settle this (see Web on the left of). If the file was already deleted, without overwriting the data, also the complete free memory of the non removable disk can be overwritten.

Different non removable disks offer the possibility, thatto protect complete non removable disk contents by password directly on hardware level. Since this characteristic useful in the reason however hardly admits is and most BIOSe does not switch the function off for setting the password automatically, purely theoretically those exists for harming programs such as virusesChance to harm the user by setting this password to an unknown value substantial insists thereafter nevertheless no more possibility of accessing still on contents of the non removable disk. For further information concerning. To ATA non removable disks see password protection under ATA.

history

Old IBM 62PC-Festplatte, approx. 1979, 6 x 8 ″ disks with altogether approx. 65 MT memory

forerunner of the non removable disk was the magnetic drum starting from 1958 (Zuse Z22). The development was determined at first by IBM (see English. Article Early IBM disk STORAGE). These systems consisted of up to 50 disks with up to 14 tariff size with memory capacities within the megabyte range.

chronological overview

  • 1956: IBM presents the first magnetic non removable disk drive assembly. On 50 recording disks of 61 cm diametersa capacity was reached by 5 megabyte (MT).
  • 1973: IBM starts „the Winchester “- project, which was concerned with it, a rotary memory with a firmly installed medium to develop (IBM 3340, 30 MT storage capacity, 30 ms access time). When startingand stopping the medium the heads on the medium should rest upon, which made a load mechanism redundant. Name giver was the Winchester rifle 3030.
  • 1979: Conception of the first 8 ″ - Winchester drive assemblies. These were however very heavy and expensive (5 MT cost more than10,000 DM (approx. 5000 euro)); nevertheless the paragraph rose continuously.
  • 1980: Sales of the first 5-1/4 ″ - Winchester drive assemblies by the company Seagate Technology with the model designation ST506 (6 megabyte of capacity). This model designation (ST506) became also beyond many years thatName for this new applied interface, which all other companies than new standard had transferred in the PC range. At the same time the first PC of IBM came on the market beside the Apple Microcomputern already existing, thus the demand for these rose- compared with the Winchester drive assemblies compact - non removable disks rapidly on.
  • 1986: First minutes for a non removable disk interface standardized specification of SCSI, one.
  • 1997: First employment of the giant Magnetowiderstands (English Giant Magnetoresistive Effect (GMR)) with non removable disks, therebythe storage capacity could be strongly increased. One of the first non removable disks with GMR read heads was IBM Deskstar 16GP (3.5 ″, November 1997) with a capacity of 16,8 GB.
  • 2004: 18. November 400 GB-non removable disk (3.5 ″) of Hitachi. First non removable disks with native ones COMMAND Queuing of Seagate.
  • 2005: 500 GB-non removable disk (3.5 ″) of Hitachi.
  • 2006: First 2,5-Zoll Notebook non removable disk (160 GB, „Momentus 5400,3 “) of Seagate with perpendicular recording technology (Perpendicular Recording)
  • 2006: April: Announcement first 750 of the GB-non removable disk („Barracuda-7200.10 “) of Seagatewith perpendicular recording technology (Perpendicular Recording) to the sales at the end of of May 2006

see also

Web on the left of

Wikibooks: Pieces of advice to the non removable disk purchase and the problems thereafter - learning and teaching materials
Wiktionary: Non removable disk - word origin, synonyms and translations


 

  > German to English > de.wikipedia.org (Machine translated into English)