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What's New in QBench 1.3?
--------------------------

     Before describing what is different in version 1.3 of QBench, first 
note that the basic structure of QBench measurements and calculations has 
not changed.  All results obtained using version 1.3 are directly 
comparable with results obtained using previous versions.  Two new 
command line options have been added, and the drive's data transfer rate 
is calculated and presented in more detail than in previous versions.  
The test methods, calculations, and even the help files and documentation 
have not changed from the originally released version 1.21.  Only this 
file, QB130NEW.TXT, documents the changes in version 1.3.

     This file only includes a description of the enhancements found in 
QBench 1.3.  No attempt is made to provide an introductory explanation of 
the workings of QBench.  Please refer to the original program help files 
and the QBINSTR user's manual file for more information.

     The enhancements for version 1.3 of QBench are:

     (1) Additional data transfer rate calculations have been added, 
reducing the reliance on data access time as the single measure of disk 
performance. 

     (2) A new option which allows QBench to be run from a batch file 
without operator intervention.

     (3) An advanced option which provides more detail on the statistical 
calculations used to obtain the data access time and the data transfer 
rate.


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(1) The Increasing Importance of Data Transfer Rate
-------------------------------------------------------

     The initial release of QBench emphasized data access time as the 
primary metric of disk drive performance.  There were two main reasons 
for this choice.  First, data access time is the most accurate single 
indicator of a drive's DOS performance, since DOS transfers are typically 
very short and thus access time is the primary component of these 
transfers.  Additionally, a drive's data access time is generally 
independent of the speed of the machine on which the test is run, and 
thus it is a good indicator of drive performance, even when the drive is 
moved from one system to another.

     Data transfer rate, as used here, is defined as the rate at which 
data is transferred, once it has been accessed.  Since the relationship 
between the size of a data transfer (in sectors) and the command service 
time required to complete that transfer (in ms) is linear and may be 
plotted as a straight line, a drive's performance characteristics may be 
completely described by the slope (in ms/sector) and intercept (in ms) of 
that line.  The data access time, as reported by QBench, is approximately 
equal to the intercept of this line.  The data transfer rate used by 
QBench is the reciprocal of the slope, with the units converted from 
sectors/ms to the more traditional KBytes/second.

     Other benchmarks which report transfer rate typically measure the 
total time required to complete a data transfer command.  This quantity 
includes not only transfer time, but also additional fixed overhead per 
command such as command overhead in the computer, drive access time, etc.  
Thus the transfer rate reported is highly dependent upon the length of 
the data transfer used in the test (how much data gets transferred for 
each command processed), and a different transfer rate is reported for 
each transfer size.  QBench's data transfer rate measure has the 
advantage of being completely independent of the transfer size.

     Note that any transfer rate measure, including QBench's data 
transfer rate, is highly system dependent, and will vary greatly due to 
differences in CPU speed and I/O bus implementation.  However, if 
different drives are measured on the same computer system, the drive-
dependent aspects of data transfer rate can be properly observed.

     Why does the new version of QBench increase the emphasis on data 
transfer rate as a measure of performance in addition to data access 
time?  There are several reasons.  Although this measure is system 
dependent, it is an important component of the overall performance of a 
computer's I/O subsystem.  Also, for operating systems other than DOS 
which transfer data in units longer than a sector or two, the data 
transfer rate accounts for an increasing proportion of the overall 
command service time.  The final reason has to do with the method QBench 
uses to calculate data access time.  Since data access time cannot be 
measured directly, it is calculated in QBench by subtracting the data 
transfer time from the command service time for a single sector transfer.  
For a given single sector command service time, a drive with a poor data 
transfer rate may appear to have a better data access time than it 
should.

     In summary, data access time and data transfer rate are intimately 
connected, and both measures should be reported to properly describe the 
performance of a hard disk.  Just remember that the data transfer rate is 
system dependent, and can only be understood in the context of the 
machine on which the benchmark is run.

     An example of the differences in QBench output between the old and 
new versions is presented below.  The lines below are found at the end of 
the "Detailed Results" section. 


QBench 1.21 output:

                             RESULTS
                    Sequential              Random          Weighted
                  Read      Write       Read      Write     Average
  Access Time:   0.47 ms    0.32 ms   16.94 ms   22.62 ms    6.99 ms*
 
  Transfer Rate KByte/Second:  956
 
______________________________________________________________________

                   * Data Access Time is 7.0 ms
______________________________________________________________________



QBench 1.3 output:

                               RESULTS
                     Sequential              Random          Weighted
                   Read      Write       Read      Write     Average
  Access Time     0.47 ms    0.32 ms   16.94 ms   22.62 ms    6.99 ms*
  Transfer Rate    859        989        949       1304        956 **
     (KB/Sec)
______________________________________________________________________

                   * Data Access Time is  7.0 ms
______________________________________________________________________

                ** Data Transfer Rate is   960 KB/sec
______________________________________________________________________
 

     The weighted average value (which is also the data transfer rate) in 
version 1.3 is the same as the value reported as Transfer Rate in version 
1.21.  In addition, version 1.3 provides detail on the contribution to 
the data transfer rate for each type of disk access.  Finally, the data 
transfer rate (rounded to the nearest 10 KB/sec to better represent the 
accuracy of the measurement) is displayed at the bottom along with the 
data access time.

     One final note: the data access time is equal to the weighted 
average (using the standard arithmetic mean) of the individual access 
times for each type of disk access, using the workload percentages 
specified in the program as weights.  For data transfer rate, the 
weighted harmonic mean of the individual transfer rates is used.


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(2) Running QBench From a Batch File
-------------------------------------

     The /O or Output option (when used in conjunction with the 
previously available /D option) allows QBench to be run from a batch file 
with the Detailed Results for the test run automatically stored in a file 
for later analysis and comparison.  This relatively minor enhancement can 
be a major improvement when a number of drives are being tested or a 
number of runs are desired for a particular drive, since all of the 
testing can be done in an automated manner without operator intervention.

     An example batch file might include the following lines:

               QBENCH /D:1 /O:RUN1.DAT
               QBENCH /D:1 /O:RUN2.DAT
               QBENCH /D:1 /O:RUN3.DAT

These three lines would cause QBench to be run three times for the first 
drive in the system, with the results of the three runs stored in the 
files RUN1.DAT, RUN2.DAT and RUN3.DAT.  Note that the /D option must be 
used in conjunction with /O for batch file operation to indicate which of 
the system drives QBench should test.


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(3) Additional Detail on Statistical Calculations
--------------------------------------------------

     Please note before reading this section that the average user will 
NOT want the additional detail provided by this option.  The /S option 
allows a user with a background in statistics to understand in detail the 
least squares curve fitting calculations used internally by QBench.  If 
QBench is invoked with the /S command line option, three lines of 
additional output will be included at the end of the Detailed Results as 
shown in the example below. 

QBench 1.3 output (with /S option):

                               RESULTS
                     Sequential              Random          Weighted
                   Read      Write       Read      Write     Average
  Access Time     0.47 ms    0.32 ms   16.94 ms   22.62 ms    6.99 ms*
  Transfer Rate    859        989        949       1304        956 **
     (KB/Sec)
______________________________________________________________________

                   * Data Access Time is  7.0 ms
______________________________________________________________________

                ** Data Transfer Rate is   960 KB/sec
______________________________________________________________________
 
  Intercept      1.145 ms   0.368 ms  17.085 ms  20.871 ms   7.052 ms
    Slope        0.582 ms   0.506 ms   0.527 ms   0.384 ms   0.523 ms
     R^2         0.998      1.000      0.999      0.979      0.999


The additional three lines show the slope and intercept of the least-
squares regression line, while R^2 ("R squared") is the square of the 
sample correlation coefficient (sometimes called the coefficient of 
determination) and shows the degree of linear fit of the data (1.000 
indicates a perfect linear fit).  Please consult a statistics textbook 
for further information on these quantities.


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