Low-level formatting .28LLF.29 of hard disks Disk formatting

low-level format of 10-megabyte ibm pc xt hard drive

hard disk drives prior 1990s typically had separate disk controller defined how data encoded on media. media, drive and/or controller possibly procured separate vendors, users able perform low-level formatting. separate procurement had potential of incompatibility between separate components such subsystem not reliably store data.

user instigated low-level formatting (llf) of hard disk drives common minicomputer , personal computer systems until 1990s. ibm , other mainframe system vendors typically supplied hard disk drives (or media in case of removable media hdds) low-level format. typically involved subdividing each track on disk 1 or more blocks contain user data , associated control information. different computers used different block sizes , ibm notably used variable block sizes popularity of ibm pc caused industry adopt standard of 512 user data bytes per block middle 1980s.

depending upon system, low-level formatting done operating system utility. ibm compatible pcs used bios, invoked using ms-dos debug program, transfer control routine hidden @ different addresses in different bioses.

transition away llf

starting in late 1980s, driven volume of ibm compatible pcs, hdds became routinely available pre-formatted compatible low-level format. @ same time, industry moved historical (dumb) bit serial interfaces modern (intelligent) bit serial interfaces , word serial interfaces wherein low level format performed @ factory.

today, end-user, in cases, should never perform low-level formatting of ide or ata hard drive, , in fact not possible on modern hard drives because formatting done on servowriter before disk assembled drive in factory.

disk reinitialization

while impossible perform complete llf on modern hard drives (since mid-1990s) outside factory, term low-level format still used called reinitialization of hard drive factory configuration (and these terms may misunderstood).

the present ambiguity in term low-level format seems due both inconsistent documentation on web sites , belief many users process below high-level (file system) format must called low-level format. since of low level formatting process can today performed @ factory, various drive manufacturers describe reinitialization software llf utilities on web sites. since users have no way determine difference between complete llf , reinitialization (they observe running software results in hard disk must high-level formatted), both misinformed user , mixed signals various drive manufacturers have perpetuated error. note: whatever possible misuse of such terms may exist (search hard drive manufacturers web sites these terms), many sites make such reinitialization utilities available (possibly bootable floppy diskette or cd image files), both overwrite every byte , check damaged sectors on hard disk.

reinitialization should include identifying (and sparing out if possible) sectors cannot written , read drive, correctly. term has, however, been used refer portion of process, in every sector of drive written to; writing specific value every addressable location on disk.

traditionally, physical sectors initialized fill value of 0xf6 per int 1eh s disk parameter table (dpt) during format on ibm compatible machines. value used on atari portfolio. 8-inch cp/m floppies typically came pre-formatted value of 0xe5, , way of digital research value used on atari st , amstrad formatted floppies. amstrad otherwise used 0xf4 fill value. modern formatters wipe hard disks value of 0x00 instead, called zero-filling, whereas value of 0xff used on flash disks reduce wear. latter value typically default value used on rom disks (which cannot reformatted). advanced formatting tools allow configuring fill value.

one popular method performing zero-fill operation on hard disk writing zero-value bytes drive using unix dd utility /dev/zero stream input file , drive (or specific partition) output file. command may take many hours complete, , can erase files , file systems.

another method scsi disks may use sg_format command issue low-level scsi format unit command.

zero-filling drive not secure method of erasing sensitive data, or of preparing drive use encrypted filesystem.

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