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A microkernel is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, thread management, and inter-process communication (IPC).
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diskpart(8) [bsd man page]

DISKPART(8)						      System Manager's Manual						       DISKPART(8)

NAME
diskpart - calculate default disk partition sizes SYNOPSIS
/usr/sbin/diskpart [ -p ] [ -d ] disk-type DESCRIPTION
Diskpart is used to calculate the disk partition sizes based on the default rules used at Berkeley. If the -p option is supplied, tables suitable for inclusion in a device driver are produced. If the -d option is supplied, an entry suitable for inclusion in the disk descrip- tion file /etc/disktab is generated; c.f. disktab(5). On disks that use bad144-style bad-sector forwarding, space is left in the last partition on the disk for a bad sector forwarding table. The space reserved is one track for the replicated copies of the table and suffi- cient tracks to hold a pool of 126 sectors to which bad sectors are mapped. For more information, see bad144(8). The disk partition sizes are based on the total amount of space on the disk as given in the table below (all values are supplied in units of 512 byte sectors). The `c' partition is, by convention, used to access the entire physical disk. The device driver tables include the space reserved for the bad sector forwarding table in the `c' partition; those used in the disktab and default formats exclude reserved tracks. In normal operation, either the `g' partition is used, or the `d', `e', and `f' partitions are used. The `g' and `f' partitions are variable-sized, occupying whatever space remains after allocation of the fixed sized partitions. If the disk is smaller than 20 Megabytes, then diskpart aborts with the message ``disk too small, calculate by hand''. Partition 20-60 MB 61-205 MB 206-355 MB 356+ MB a 15884 15884 15884 15884 b 10032 33440 33440 66880 d 15884 15884 15884 15884 e unused 55936 55936 307200 h unused unused 291346 291346 If an unknown disk type is specified, diskpart will prompt for the required disk geometry information. SEE ALSO
disktab(5), bad144(8) BUGS
Certain default partition sizes are based on historical artifacts (e.g. RP06), and may result in unsatisfactory layouts. When using the -d flag, alternate disk names are not included in the output. 4th Berkeley Distribution November 17, 1996 DISKPART(8)

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BAD144(8)						      System Manager's Manual							 BAD144(8)

NAME
bad144 - read/write DEC standard 144 bad sector information SYNOPSIS
bad144 disktype disk [ sno [ bad ... ] ] DESCRIPTION
Bad144 can be used to inspect the information stored on a disk that is used by the disk drivers to implement bad sector forwarding. The format of the information is specified by DEC standard 144, as follows. The bad sector information is located in the first 5 even numbered sectors of the last track of the disk pack. There are five identical copies of the information, described by the dkbad structure. Only the first of these copies is used. Replacement sectors are allocated starting with the first sector before the bad sector information and working backwards towards the begin- ning of the disk. A maximum of 126 bad sectors can be supported. The position of the bad sector in the bad sector table determines which replacement sector it corresponds to. The bad sector information and replacement sectors are conventionally only accessible through the ``h'' file system partition of the disk. If that partition is used for a file system, the user is responsible for making sure that it does not overlap the bad sector information or any replacement sectors. The bad sector structure is as follows: struct dkbad { long bt_csn; /* cartridge serial number */ u_short bt_mbz; /* unused; should be 0 */ u_short bt_flag; /* -1 => alignment cartridge */ struct bt_bad { u_short bt_cyl; /* cylinder number of bad sector */ u_short bt_trksec; /* track and sector number */ } bt_bad[MAXBAD]; }; Unused slots in the bt_bad array are filled with all bits set, a putatively illegal value. MAXBAD (in <sys/dkbad.h>) may be tuned locally to reduce the space required to hold the bad-sector file in memory. It may not be greater than 126, which uses the whole disk sector. Bad sectors past MAXBAD may be included by the formatter, but replacement sectors will not be used until MAXBAD is increased. Bad144 is invoked by giving a device type (e.g. rk07, rm03, rm05, etc.), and a device name (e.g. hk0, hp1, etc.). It reads the first sec- tor of the last track of the corresponding disk and prints out the bad sector information. It may also be invoked giving a serial number for the pack and a list of bad sectors, and will then write the supplied information onto the same location. Note, however, that bad144 does not arrange for the specified sectors to be marked bad in this case. This option should only be used to restore known bad sector information which was destroyed. New bad sectors can be added by running the standard DEC formatter in section ``bad.'' SEE ALSO
badsect(8) BUGS
Not all drivers support bad-sector forwarding on the PDP-11. It should be possible to both format disks on-line under UNIX and to change the bad sector information, marking new bad sectors, without running a standalone program. The bootstrap drivers used to boot the system do not understand bad sectors or handle ECC errors. This means that none of these errors can occur when reading the file /unix to boot. Sector 0 of the disk drive and the file /boot in the root file system of that drive must also not have any of these errors in it. The drivers that write a system core image on disk after a crash do not handle errors; thus the crash dump area must be free of errors and bad sectors. 3rd Berkeley Distribution BAD144(8)

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