8mb cache disabled within windows?

[hpglow]

I heard a rumor that certin versions of windows will disable the 8mb cache on drives that contain it. Is this true or just one of thoes rumors? If so how do I enable it?

I have a couple drives with 8mb cache and I just wanted to know. I run Win2k btw...

 

[enyceexdanny]

If it's an 8MB cache drive, then it's 8MBs. The cache runs on a hardware level, so I don't think windows can disable or modify that.

 

[aug1516]

Originally posted by enyceexdanny
If it's an 8MB cache drive, then it's 8MBs. The cache runs on a hardware level, so I don't think windows can disable or modify that.

I think this is the way it is. I don't know if windows even knows, or cares about how much cache your hard drive has.

 

[Snugglebear]

Windows, or any other modern OS for that matter, can enable or disable the use of disk cache at will. If you dig around in your ATA controller and disk properties you'll see a couple checkboxes related to caching. One is to disable write caching, the other is to disable read ahead caching. Occasionally, if Windows thinks you've got a controller or drive that is known to be finnicky, it will disable these and possibly also drop into PIO mode. 99% of the time both will be enabled and working fine. There are some situations where you would deliberately want these disabled, but then as desktop users you'll probably never encounter them.

 

[Ice Czar]

you would check a drive's write cache setting via
Start > Run > (type) compmgmt.msc > Device Manager > Expand Disk Drives > (DClick) the Drive to check > Disk Properties Tab > check, "Write cache enabled"

you would verify the current transfer mode like:
Device Manager > Expand IDE ATA\ATAPI Controllers > check applicable Primary & Secondary IDE Channel (DClick) > Advanced Sttings Tab > check, Current Transfer Mode for both Device 0 & 1

Windows will default both devices on a channel to PIO if one of them is downgraded to PIO (and that is glacially slow, best possible mode being 16.7MB/s)
Independent Device Timing for the Master Slave devies, a function that allows each to run at their own individual highest speed) can not function if one device is in PIO and the other in DMA or more likely UDMA.

a few reasons why DMA might not be enabled by default

DMA Mode for ATA/ATAPI Devices in Windows XP

The Microsoft® Windows® XP operating system enables DMA by default on most of the ATA or ATAPI (IDE) devices. To ensure system stability, however, PIO mode will be selected for DMA-capable devices under some circumstances. This article explains the reasons for an ATA or ATAPI device to be in PIO mode on systems running Windows XP.

PIO mode is enabled by default in the following situations:

• For ATAPI devices, except DVD and CD-R/RWW drives. Windows XP enables PIO by default on ATAPI tape drives, CD-ROM drives, and ATAPI removable drives such as magneto-optical (MO) drives. The user can, however, enable DMA on an ATAPI device through Device Manager, as described at the end of this article.


Windows XP enables DMA by default on ATAPI DVD and CD-RW/CD-R drives.


• For ATA or ATAPI devices that do not work properly in DMA mode. Compatibility testing at Microsoft has shown that enabling DMA on certain drives could cause data corruption or reduced system stability. There is no way for the user to enable DMA on these devices.

• For certain IDE chipsets that cause data corruption. For ATA or ATAPI devices using chipsets that are known to cause problems running in the DMA mode, Windows will enable PIO by default.


System manufacturers can override this default behavior by implementing the _GTM and _STM methods in the ACPI BIOS. Also, the user can enable DMA using the Device Manager.


• For repeated DMA errors. Windows XP will turn off DMA mode for a device after encountering certain errors during data transfer operations. If more that six DMA transfer timeouts occur, Windows will turn off DMA and use only PIO mode on that device.


In this case, the user cannot turn on DMA for this device. The only option for the user who wants to enable DMA mode is to uninstall and reinstall the device.

Windows XP downgrades the Ultra DMA transfer mode after receiving more than six CRC errors. Whenever possible, the operating system will step down one UDMA mode at a time (from UDMA mode 4 to UDMA mode 3, and so on).

If the mini-IDE driver for the device does not support stepping down transfer modes, or if the device is running UDMA mode 0, Windows XP will step down to PIO mode after encountering six or more CRC errors. In this case, a system reboot should restore the original DMA mode settings.

All CRC and timeout errors are logged in the system event log. These types of errors could be caused by improper mounting or improper cabling (for example, 40-pin instead of 80-pin cable). Or such errors could indicate imminent hardware failure, for example, in a hard drive or chipset.

If your experiencing the last senerio, where DMA keeps getting downgraded, its more likely than not a poor connection, crappy cables, or interference, followed by the device itself or the controller busmaster driver.
See Corrupted Files

Independent Device Timing and Windows downgrading devices to PIO are the two reasons that the myth about how bad it is to share a channel between a HDD and Optical Drive is still perpetuated so vigourously, it was true once apon a time, but no longer, actually for a machine where you are regularly transfering data from one HDD to another and also have 2 optical, its probably better to place a HDD & Optical on each channel, the Opticals are rarely accessed, and even when burning from the HDD to the Optical on the same channel, its extremely rare there are any issues (with modern burning software) but when transfering large amounts of data at DMA mode 5 from a HDD to a HDD on the same chennel, it will slow down, as IDE is sequential.