"PCI Latency" patch for VIA Chipsets

All executable and document files of this "PCI Latency" patch are Copyright (C) 2001-2003, George E. Breese. All Rights Reserved.

Version 0.20 BETA build 21
June 12 2003

Important notes:

This BETA version of the patch has been provided for experimental testing use only. It contains a mix of known-good settings and experimental ones. Do not distribute it.

Your computer's motherboard must contain a complete VIA chipset in order for this patch to work. Check the model of chipset by downloading and running CPUZ. If the Mainboard section of CPUZ does not show a VIA chipset in the computer, then this patch will not work.

This product could, in a rare case, damage a computer. Use it carefully and at your own risk. By using it, you agree to the license as shown below.

If you have installed a previous version of this driver, uninstall it before installing this version.


All credit for the original research on this patch is given to the site au-ja! Their page review-kt133a-1.html describes the problem and solution in German. Version 0.10 of this patch was based entirely upon the recommendations of au-ja!.

I wish to thank the staff of Sudhian.com (formerly VIAHardware.com) for promoting my work. They have been supportive of my drivers since I first began creating them. I also wish to thank WiNC, Franck, and all the testers who helped refine and define the patch.

Thanks to Ryan of OCZTech.com for providing additional hardware for testing.

Thanks to Sinjin for donating a sample of the Asus A7V133 motherboard for testing. This motherboard was discontinued by Asus and was becoming hard to find when I needed it to test a compatibility issue with version 0.19 of the patch.


This software is licensed, not sold. The author of this product has granted you a license to use this product, subject to the following conditions. By possessing, using, or attempting to use this product, you assume all liability for its use. You agree never to take legal action, civil or criminal, against its author for any reason. You may redistribute this product in its original form only. You may not charge money for distribution of the product, unless all such charges are remitted to the author immediately upon payment. The author retains ownership of all intellectual properties embodied in this product.

About This Product:

This is a "patch" that can be applied to computers in order to solve problems with the computer's PCI bus. This patch is designed for computers whose chipset was made by VIA. You can discover the maker of your computer's chipset by downloading and running CPUZ from www.cpuid.com , and examining the Mainboard information.

This patch is commonly used to fix problems with sound cards, with USB connections, or with IDE hard disks and DVD-ROM or CD-RW drives. But, it can be used to help the performance of any PCI card in a VIA-based computer.

The changes made by this product are temporary. The computer's chipset erases all changes automatically when being restarted, so the "patch" program must reapply the changes each time Windows is started.

Installing the patch:

If you can read this file, the patch has been installed.

The patch is normally installed by downloading and opening VLATENCY_XXX.EXE, where XXX is the version of the patch.

Uninstalling the patch:

In the "Add / Remove Programs" section of Control Panel, find the PCI Latency Patch and press the button to remove it. If the computer is unstable, please start Windows in Safe Mode before trying to uninstall the patch.

Files included:

VLATENCY.SYS - is the program file containing the patch for Windows 98, ME, NT 4.0, 2000, and XP. It is copied to WINDOWS\SYSTEM32\DRIVERS.

VLATENCY.INF - is the configuration file describing the installation of the patch. It is copied to WINDOWS\INF.

PCI Latency Patch README.HTM - is this file. It contains warnings, quick instructions, and last-minute information. It is copied to the Windows desktop.

Release Notes:

Version 0.20 beta 21

Version 0.20 beta 20

Version 0.20 beta 19

Version 0.20 beta 18

Version 0.20 beta 17

Version 0.20 beta 16

Version 0.20 beta 15

Version 0.20 beta 14

Version 0.20 beta 12

Version 0.20 beta 11

Version 0.20 beta 10

Version 0.20 beta 9

Version 0.20 beta 8

Version 0.20 beta 7

Version 0.20 beta 6

Version 0.20 beta 5 no longer sets high latency for IDE/RAID/SCSI controllers. It also corrects the value of the round-robin policy in register Rx76 to 01 for new chipsets.

Version 0.20 beta 4 sets registers 0D, 55, 70, 75, and 76 differently for old chipsets than for new ones. It also disables PCI Master Broken Timer, sets high latency for all IDE/RAID/SCSI controllers, and some previous patch items were removed.

Version 0.20 beta 3 fixes a bug, only found in previous 0.20 betas, that would clear bits 6 and 7 of register Rx75. This version also has the PCI Master Read Caching re-enabled, but only for KT133/KM133/KLE133 chipsets.

Version 0.20 beta 2 disabled PCI Delay Transaction, which was missing from the first beta. It also forces the MWQ register to 100 to hopefully fix video corruption on KLE133 chipsets. And, it disables PCI Master Read Caching, and sets the Guaranteed CPU Time (0D) register to 02 instead of 00. But, please note that you can't read register 0D directly in PCI tools such as WPCREDIT, because the bottom bits are designed to always read 000.