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Full Discussion: dd bytesize
Top Forums UNIX for Advanced & Expert Users dd bytesize Post 302515146 by pludi on Tuesday 19th of April 2011 08:25:19 AM
Old 04-19-2011
"bs" is the block size, not the byte size (a byte is always 8 bits). Reasons you might want to use it:
  • To transfer a certain amount of fixed-size records (using bs and count options)
  • To match the block size of a device, thus reducing I/O blocking (eg. for hard disks and tapes)
  • To make use of a large buffer, thus reducing I/O requests

Simple example: you want to create a backup of the master boot record prior to changing the layout, it's as simple as dd if=/dev/sda of=part_table.backup bs=512 count=1, since the MBR is exactly the 512 bytes at the beginning of the disk (including boot loader, partition table, ...)
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FDISK(8)						    BSD System Manager's Manual 						  FDISK(8)

NAME
acorn-fdisk -- partition editor for Acorn/RISC OS machines SYNOPSIS
acorn-fdisk -h | --help | -v | --version acorn-fdisk [-t scheme | --type scheme] -l | --list [device ...] acorn-fdisk [-t scheme | --type scheme] -s | --size partition acorn-fdisk [-t scheme | --type scheme] [device] DESCRIPTION
The acorn-fdisk utility allows one to display or interactively edit partition tables for Acorn/RISC OS machines in various formats. Using the PC/BIOS format, standard IBM PC (i386) partition tables can also be accessed. When no optional device is given, it defaults to /dev/hda or /dev/sda. The options are as follows: -h | --help Display a short usage and exit immediately. -l | --list Display the partition table(s) of all devices. -s | --size Display the size of partition. -t | --type Select the partitioning scheme to use. Valid schemes are: EESOX Eesox SCSI on the Acorn machines. ICSIDEFS ICS IDE. Filecore/Linux Linux on Filecore. This uses the non-ADFS descriptor to point to the start of the disc to be partitioned. The first two sectors contain a partition table to identify the Linux partitions contained within. PC/BIOS PC/BIOS partitioning scheme. This consists of a partition table in the first sector of the disk which contains both CHS and LBA values for the partitions. There can be up to four entries in the primary partition table. One of these can be an extended partition containing up to four extra partitions. PowerTec PowerTec SCSI on the Acorn machines. Filecore/RISCiX RiscIX on Filecore. -v | --version Display the version of acorn-fdisk and exit immediately. If neither -l | --list or -s | --size are given, the partition table of the given device will be edited interactively. EXAMPLES
Display the default device's partition table on a PC: acorn-fdisk --type PC/BIOS -l Display the PC partition table of /dev/sda: acorn-fdisk --type PC/BIOS --list /dev/sda Display the size in blocks of the partition /dev/sda1: acorn-fdisk --type PC/BIOS --size /dev/sda1 Edit the MBR partition table interactively: acorn-fdisk --type PC/BIOS Display the partition table of an MBR backed up to a file: acorn-fdisk -t PC/BIOS -l mbrdump.bin Display the size of the first partition on a device where the MBR would be restored from the backup file mbrdump.bin: acorn-fdisk -t PC/BIOS -s mbrdump.bin1 AUTHORS
arm-fdisk was written by Russell King <rmk@arm.uk.linux.org> based on util-linux fdisk, which was written at least partially by A. V. Le Blanc <LeBlanc@mcc.ac.uk>. This manual page was written for the Debian system by Thorsten Glaser <tg@debian.org> but may be used by others. BSD
October 2, 2010 BSD
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