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    Length: 2758 (0xac6)
    Types: TextFile
    Notes: UNIX file
    Names: »dc.4«

└─⟦26887b7e0⟧ Bits:30009717 Comet 32 harddisk image
    └─⟦28c352965⟧ »/a« UNIX Filesystem
        └─⟦this⟧ »usr/man/man4/dc.4« 

TextFile

.ig
	@(#)dc.4	2.1	7/1/84
	@(#)Copyright (C) 1983 by National Semiconductor Corp.
..
.TH DC 4
.SH NAME
dc \- SYS32 disk driver for ANSI interface disks
.SH DESCRIPTION
Files with minor device numbers 0 through 7 refer to various portions
of drive 0;
minor devices 8 through 15 refer to drive 1, etc.
The standard device names begin with \*(lqdc\*(rq followed by
the drive number and then a letter a-h for partitions 0-7 respectively.
The character `?' stands here for a drive number in the range 0-7.
.PP
It is unwise for all of these files to be present in one installation,
because there is overlap in addresses and protection becomes
a sticky matter.
The dc?a partition is normally used for the root file system,
the dc?b partition as a paging area, 
the dc?c partition for pack-pack copying (it maps the entire disk).
On large disks, the dc?h partition is inserted prior to the dc?d or
dc?g partition; the dc?g partition then maps the remainder of the pack.
.PP
The block files access the disk via the system's normal
buffering mechanism and may be read and written without regard to
physical disk records.
A `raw' interface,
which provides for direct transmission between the disk
and the user's read or write buffer, is also available.
A single read or write call results in exactly one I/O operation
and therefore raw I/O is considerably more efficient when
many words are transmitted.
The names of the raw files
conventionally begin with an extra `r.'
.PP
In raw I/O counts must be a multiple of 512 bytes (one page), and the
buffer address must be a multiple on 512 (i.e., be page-aligned).
This is a restriction imposed by the disk controller.
Attempts to perform I/O
without following these restrictions results in an EIO error.
Likewise
.IR lseek (2)
calls should specify a multiple of 512 bytes.
.SH "DISK SUPPORT"
This driver supports any ANSI interface drive that contains a valid header
(as described by
.IR disk (5))
on physical sector 0.
The drive header is read off each pack and used to
initialize the driver with the disk configuration information,
and the origin and size (in sectors) of the psuedo-disks.
The origin and size of the psuedo-disks may be changed with
.IR mkpt (8).
.SH FILES
.nf
.ta \w'/usr/include/sys/disk.h'u+(4n)
/dev/dc[0-7][a-h]	block files
/dev/rdc[0-7][a-h]	raw files
/usr/include/sys/disk.h	disk header layout
.fi
.SH DIAGNOSTICS
.BR "%s disk %s error: unit %d sector %d status %x retries %d" .
This message appears on the console when a disk error occurs.
The status indicates the reason for the error.
The
.IR dcerr (8)
program can be used to decode the status.
.SH "SEE ALSO"
disk(5),
mkpt(8)
.SH BUGS
The page-alignment restriction for raw I/O should not exist.
.PP
Bad block forwarding is not yet supported.