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Busmastering: Intel vs Microsoft

  March 11, 1998 Author: Eugene Ra  

When StorageReview.com initially began tests on our first roundup of ATA drives, the 6.4GB UDMAs, we installed Intel's PIIX v3.01 drivers to control the PIIX4 chip found on the Abit LX6 motherboard. Intel's drivers were notorious for inflating results in benchmarks with no corresponding real-world performance gain, including ZDBOp's WinBench 97. However, ZD took steps to correct the problems; WinBench 98 is no longer susceptible to the same limitations. After the benchmarks were complete, reports started to surface (starting at Dan Chadwick's tweakit.com) that the PIIX drivers did nothing to help performance while in fact grossly raising CPU utilization during disk reads over the stock bus master drivers found in Windows 95 OSR2. Though it was overshadowed by the introduction of FAT32, IDE Bus Mastering was a substantial storage-related upgrade included the new revision of Win95. Many were already in the habit of using the PIIX drivers, though, and did not bother to compare what OSR 2 offered vs Intel's drivers.

Bus Master Drivers: Intel PIIX v3.01 vs OSR 2*
Ziff Davis WinBench 98  (Average of 5 trials) Intel PIIX v3.01 OSR 2.1
Model IBM DHEA 36480 IBM DHEA 36480
Business Disk WinMark 98 1346 KB/sec 1362 KB/sec
SS/Database 1192 KB/sec 1202 KB/sec
WP 1618 KB/sec 1668 KB/sec
Publishing 1260 KB/sec 1270 KB/sec
Browsers 1546 KB/sec 1554 KB/sec
Task Switching 1748 KB/sec 1726 KB/sec
High-End Disk WinMark 98 4022 KB/sec 3910 KB/sec
AVS/Express 3.1 2614 KB/sec 2382 KB/sec
Frontpage 97 3008 KB/sec 3092 KB/sec
Microstation 95 8798 KB/sec 7586 KB/sec
Photoshop 4.0 3132 KB/sec 3200 KB/sec
Premiere 4.2 7494 KB/sec 7440 KB/sec
PV-Wave 6.1 2870 KB/sec 2828 KB/sec
Visual C++ 5.0 8486 KB/sec 8722 KB/sec
Disk/Read Random Access 14.9 ms 15.0 ms
Disk/Read Transfer Rate
Beginning 10300 KB/sec 10300 KB/sec
End 6460 KB/sec 6460 KB/sec
Disk/Read CPU Utilization 35.2% 5.2%
Transfer Rate 10331 KB/sec 10334 KB/sec
Test Bed
Abit LX6 Motherboard v1.1  Intel Pentium II 266MHz, 512k cache   64MB SDRAM   IBM DHEA 36480   Matrox Millennium II PCI 4 MB
Windows 95 OSR 2.1   Intel 82371xB INF Update   Microsoft Removable IDE Patch   MGA Powerdesk v3.80   1024x768 x 24-bit color @ 85Hz

To obtain the benchmark results tabulated on the left, Storage Review used a plain installation of Windows 95 OSR 2.1. We then patched the default installation with Intel's 82371xB INF Update (also known as setupex.exe, needed to recognize the newer 430TX and 440LX chipsets) and Microsoft's Removable IDE Device Patch. Finally, under the test drive's entry in System Properties' Device Manager we checked the "DMA" box, enabling the OSR2 Bus Mastering drivers. The PIIX results were obtained by taking this configuration and also installing Intel's PIIX v3.01 drivers. IBM's Deskstar 5 6.4GB drive, posting the highest scores of all the ATA drives tested, was selected as the test drive for Bus Mastering effects.

The benchmark figures indicate that installing the PIIX drivers results in a slight but negligible hit (1.2% decrease) in WinBench's Business Disk WinMark 98 score. The reverse is true when looking at the High-End WinMark 98, there is a slight increase (2.8%). Disk/Read Random Access and Transfer Rates remained the same. However, Disk/Read CPU Utilization jumps an astounding 677%, up to 35.2% from 5.2%.

It is often said by SCSI proponents that ATA drives cannot touch the miniscule CPU utilization posted by SCSI drives. This is simply untrue. The perception is likely perpetuated simply because most run tests using PIIX vs SCSI instead of OSR2 vs SCSI. While SCSI still holds benefits over ATA devices in many areas, CPU utilization is not one of them. Its important to note that to achieve the low CPU utilization scores (along with an increase in the sequential data transfer rates) that the drive's individual DMA box must be enabled. Leaving the box unchecked will result in CPU Utilization scores in the 80-90% range.

Users still running the original release of Windows 95 still benefit from installing Intel's PIIX drivers. However, those running OSR2 should simply stick with the built-in Bus Mastering drivers. OSR2 not only offers more efficient space utilization with FAT32, it brings SCSI-like CPU utilization levels to the table.

* Note: All reported test results are the average of five trials.


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