2. COST ACCOUNTING CONCEPTS FOR IS ORGANIZATIONS › 2.3 Resource Accounting

2.3 Resource Accounting

In the early days of computing, when only one task at a time
could run on a machine and any task used virtually all of the
machine's associated resources, the elapsed time to run the
job was an adequate measure of utilization.  This method
charged a job according to the amount of time the job resided
in the system.  Today, with advances in technology, the
elapsed time is a function of the multiprogramming mix and
cannot be controlled by the user.  The elapsed time method of
charging provides inconsistent as well as inequitable results
for everyone concerned.  Almost every advance in technology
has made it more difficult to determine who used what and
when.

Numerous methods for determining resource utilization have
been developed.  The common factor among all of them is the
attempt to approximate a measure equivalent to the classical
elapsed time.

Resource accounting is the technical method of accounting for
resource utilization.  Usage is measured in terms of
definable computer resources such as CPU time, I/O, and
memory, as opposed to accounting based on work performed (for
example, checks produced).  For accounting purposes, the
resources available to a unit of work fall into three
categories:  dynamic resources, dedicated resources, and
miscellaneous resources.


DYNAMIC RESOURCES

CPU time and channel time are dynamic resources.  CPU time is
the amount of time the task is in control of the CPU.
Channel time is, at best, a measure of the time taken to
transfer data from main storage to devices and back.  These
resources are charged out according to actual utilization.
In other words, the system might charge out CPU time at
$260 per hour of utilization and channel time at $32 per
hour.

DEDICATED RESOURCES

Dedicated resources consist of main storage and all I/O
devices.  These are charged not according to utilization, but
according to the time the user has been responsible for their
allocation.  For example, the true costs of a tape drive,
once data transfer time to the device has been considered, is
not the utilization time, but the time that it has been
allocated and therefore unavailable for use by any other job.


MISCELLANEOUS RESOURCES

Miscellaneous resources are comprised of spooling costs and
operator costs.  These resources should be charged according
to the number of times they occur.  Spooling costs include
print lines,as well as the use of special forms.  Operation
costs are items such as volume mounts and operator message
replies.  A typical charge for a job includes the charge for
the number of print lines used to print the output and a
charge for each volume mount required by the job.

The following sections outline different types of resource
accounting methods:

    1 - CPU Time
    2 - CPU Time/Memory Utilization Accounting
    3 - CPU Occupancy Time
    4 - Transaction Residency Time
    5 - Resource Occupancy Time