V8/usr/man/man4/drum.4

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.TH DRUM 4
.SH NAME
drum \- paging device
.SH SYNOPSIS
This file refers to the paging device in use by the system.
This may actually be a subdevice of one of the disk drivers, but in
a system with paging spread across multiple disk drives or interleaved
will be an indirect driver.
.SH FILES
/dev/drum
.SH BUGS
Reads from the drum are not allowed across the interleaving boundaries.
Since these only occur every
.BR . 5Mbytes
or so,
and since the system never allocates blocks across the boundary,
this is usually not a problem.