6 Configuration

Yes. Often these drivers are essential to get any kind of performance out of your interface.

The PIO or DMA mode used when transferring data is determined by the interface card. Some cards have jumpers that determine the speed in hardware; these work in the fast mode from the microsecond you switch on the computer.

Most interfaces, however, are software configurable. At bootup, they default to the slowest possible speed. Somewhere during the boot process, a piece of software belonging to your adapter figures out what kind of transfer rates the drives support and configures the controller chip to match. There are a couple of cases to distinguish:

• Onboard I/O with full BIOS support. The controller is fully configured when your computer boots. You can usually set the desired mode for each harddisk in the CMOS setup. Many modern boards fall in this category.
• Onboard I/O with incomplete BIOS support. For some unfathomable reason, some mainboards do not support or only imperfectly set up their integrated I/O ports. In that case, you'll have to use DOS or other drivers to get full functionality.
• Interface card with BIOS. This is similar to the two categories above. The main difference is that these cards don't necessarily have setup screens; in that case, they must use other means to determine the transfer mode to be used. For example, the Promise 2300+ uses a combination of jumpers and a table in ROM containing the parameters for a number of different drives. It may or may not be necessary to use drivers for best performance.
• Interface card without BIOS. Since there is no way the mainboard BIOS can know how to set up all those different interface cards out there, you must use the supplied device drivers to profit from the fast modes. That is, unless your card is hardware configurable using jumpers, which is quite rare.

Usually, there are drivers for other operating systems as well, such as Windows, Win95, OS/2 and so forth. These serve a couple of purposes.

The difference between the three is this.

• 'Normal' causes the BIOS to behave like an old fashioned one without translation. Use this if your drive doesn't need it (ie. has fewer than 1024 cylinders) or if you want to use the drive with an operating system that doesn't understand about translation.
• 'Large' or ECHS or XCHS tells the BIOS to use CHS translation. It uses a different geometry (Cylinders/Heads/Sectors) when accessing the drive than when talking to the software through int13. This type of translation works with all drives.

  Note. Some BIOSes have a braindead Large implementation which works only for disks of up to 1GB. Fortunately, all larger disks support LBA.

• 'LBA' differs from 'Large' in that it uses LBA addressing to access the harddisk. The advantage is that it theoretically is a little faster. The disadvantages are that some older drives don't support it, and it often turns out to be slower, depending on the drive.

WARNING. Some BIOSes change the (translated) geometry if you change from Normal or Large to LBA. The same thing may happen if you transfer a disk that has been formatted on an old, non-LBA computer to a new one that uses LBA. This has destroyed data. Don't let it happen to you.

Unfortunately, no. Proceed with care.

While with many BIOSes, the sectors on the disk are addressed in the same order independent of the translation mode, a few use a different type of translation algorithm. The latter type of BIOS will shuffle your data as if it were a deck of cards if you alter the translation mode.

Moreover, BIOSes that conform to the WD Guide may use completely dissimilar drive geometries in the software (int13) interface depending on the translation mode. If this happens it will wreak havoc with your data. This represents a major flaw in the WD EBIOS specification.

In both of these cases, after changing the translation mode, you must repartition and reformat your disk.

The only reason why you would want to enable this option is that DMA modes are less likely to corrupt data than PIO modes. There will be no difference in CPU usage. (when DMA/33 arrives, the improved bandwidth will be another reason).

Unfortunately, at least one user has reported a drastic decline in drive throughput with DMA enabled. The reasons are unclear, so YMMV.

There's nothing wrong; this is a limitation of the DOS FAT and Win95 VFAT filesystems. You will have to create multiple partitions in order to use the full drive size.

This limitation has been addressed in Microsoft's new FAT32 filesystem, currently only available in the Win95 OEM 2 release. It allows giant multi-gigabyte partitions. At the time of writing this release can be sold with new hardware only and is unavailable to ordinary mortals.

Some try to work around the 504MB / 1024 cylinders issue by making a large partition using a friend's computer, Linux' fdisk, or something else. They use it for a day or two, conclude that it works, then post a triumphant article claiming that they found the Solution To Everyone's Problems[TM].

It will work... for precisely 1024 cylinders. The very moment the OS or anything else attempts to write something to cylinder 1025 through int13 calls, the write wraps around to cylinder 0. This cylinder happens to hold some of the most important data structures on the disk: the Master Boot Record, partition table, both FAT copies and the root directory of the first partition. Overwrite these and probably only a specialized data recovery company will be able to salvage your data.

Try it if you must. If you know exactly what you're doing, you can make it work using Win95. Sort of. The first error will be fatal. But please don't post any stories about it, recommending the procedure to everyone. The spectres of their valuable data will come back to haunt you.

This is a convenient option, but there are caveats.

The software, sometimes bearing an exotic name depending on the licensee, is usually a version of either MicroHouse's EZ-Drive or OnTrack's Disk Manager. Disk Manager, when used on the boot drive, has to resort to some trickery in order to be loaded very early during the boot process (which is necessary for technical reasons). This is accomplished by modifying the Master Boot Record (MBR), the first piece of code the BIOS loads and executes when the computer boots, and storing a Dynamic Drive Overlay (DDO) on the very first disk track. EZ-Drive works in a similar fashion.

An annoying side effect of using a software solution is that operating system installations, which often overwrite the MBR, will render the contents of your harddisk inaccessible. You will need to restore the MBR from the installation floppy to regain access to your partitions.

Moreover, such software tends to create partitions quite different from 'standard' translation schemes as used by most Enhanced BIOSes. Many device drivers dealing with the disk will fail even if they work fine with other schemes. Important examples are (E)IDE interface drivers; remember that without these drivers an interface will in general be much slower. You'll need drivers that are specifically aware of the translation software you use. Also, many operating systems other than DOS will not be able to access or use the drive, at least not 'out of the box'. Disk fixing utilities may fail to work if the partition table or the overlay is damaged.

If you have a Disk Manager or EZDrive partition and are upgrading to a translating BIOS, you have three options.

This software is usually installed in the boot drive's Master Boot Record (MBR). Normal repartitioning and reformatting of the drive usually does not refresh the MBR, which can make for a frustrating experience. Fortunately, it's not very hard once you know how.

The best way to deinstall is to follow the procedure outlined in the utility's documentation. If this is not available, the following procedure usually works: boot from a clean floppy with at least DOS, FORMAT.COM and FDISK.COM on it. Then type FDISK /MBR. This should refresh the code in your MBR. After that, repartition and reformat as usual.

Do not confuse this with Smartdrive (or whatever) lazy writes: what is meant here is altering the drive's buffer cache management algorithm. This is possible using newer versions of Drive Rocket, with hdparm under Linux, and probably other utilities too. Provided, of course, the drive supports this feature. Sometimes it can also be done using jumpers on the drive.

There seem to be problems with this, if a program will issue a soft-reset (which on Intel Pentium Motherboards also issues a hardware-reset) as soon as it sees the last IRQ, which overall ends up corrupting data. Use with care, and backup.

MS-DOS assigns drive letters as follows.

• Letters a: and b: are reserved for floppy drives.
• All primary partitions on all (system and adapter) BIOS supported harddisks get their drive letters starting from c:, in order. Normally, you can have just one primary DOS/Windows partition on every drive.
• Only then, all logical drives inside extended partitions get their letters. This means, for example, that if you had one drive with c: and d:, adding a second drive with one primary partition on it will bump the former d: partition up to e:. If you want to avoid this, do not define primary partitions on all drives except the first one.
• After that, MS-DOS parses the CONFIG.SYS and AUTOEXEC.BAT files. Some devices such as CD-ROMs have no BIOS support and get their drive letters only here.