The SCSI and CD-ROM support built into Windows 95 requires that CD-ROM drives provide SCSI parity to function properly. For many drives, this is a configurable option or is active by default. Examples of drives that do not provide or support SCSI parity are the NEC® CDR-36 and CDR-37 drives.
If you have trouble with a SCSI drive, make sure the SCSI bus is set up properly (refer to your hardware documentation for specific details).
In some cases, adding or removing a SCSI adapter might prevent your computer from starting correctly. Check the following:
If you have only internal or only external SCSI devices, the ends of the bus are probably the SCSI adapter and the last device on the cable. If you have both internal and external SCSI devices, the adapter is probably in the middle of the bus and should not have terminators installed. If you disconnect a device that has terminators installed (such as an external CD-ROM drive), be sure to install terminators on whatever device then becomes the last one on the bus. One of the devices on the SCSI bus (usually the adapter) should be configured to provide termination power to the bus.
Windows 95 supports up to seven external SCSI devices in a chain, plus internal connections. In addition to the requirement that the last external and last internal SCSI device must be terminated, some hardware has additional requirements for where it must be placed in the SCSI chain.
If you have a SCSI hard disk drive that uses removable media, such as a cartridge drive, make sure the media is mounted on the drive before running Setup. If no media is mounted on the drive, errors might occur during Setup that prevent installation of Windows 95.
For many SCSI hardware devices, you can specify command-line parameters when the driver is loaded. By default, the Windows 95 miniport driver runs without parameters (in the same way it does for real-mode drivers). If you want to use a command-line parameter, you can add it to the Settings property for the SCSI controller. For real-mode parameters that the controller supports (and if the device has a Windows 95 .MPD file), you can enter parameters in the Adapter Settings box in the controller's properties.
For information about the switches that can be used for a particular SCSI device, see the documentation from the device manufacturer. There are no additional parameters added by Microsoft.
For example, if your SCSI adapter has full functionality under MS-DOS, but not under Windows 95, you can add any device parameters previously specified in CONFIG.SYS to the Adapter Settings box. As another example, for Adaptec 7700 SCSI devices, you might specify removable=off to disable support for removable media if you want to load another ASPI removable disk.
Windows 95 needs exact SCSI ID information for Toshiba 3201, NEC 3x, and Texel 5201 CD-ROM drives. To make this information available to Windows 95, you must run the Add New Hardware wizard in Control Panel and manually choose to install specific hardware rather than running automatic detection of new hardware.
If you are running MSCDEX.EXE and it loads real-mode drivers, you cannot load protected-mode drivers from a CD-ROM. In this case, you should comment out the lines in the AUTOEXEC.BAT and CONFIG.SYS files that MSCDEX.EXE placed there. For example:
rem device=c:\sbrpo\drv\sbpcd.sys/d:mscd001 /p:220
rem c:\windows\command\mscdex.exe /s /v /d:mscd001Then you should restart the computer to allow Windows 95 to automatically detect the CD-ROM drive and its protected-mode drivers.
Notice that Windows 95 will automatically comment out these lines if the protected-mode drivers are on the CD-ROM from which you installed the drivers; that is, if you choose automatic detection, Windows 95 detects the hardware and its drivers and automatically comments out the real-mode drivers.
Windows 95 Setup does recognize multiple CD-ROM drives connected to the same SCSI host adapter. Therefore, if it doesn't recognize one of the CD-ROM drives, it is a hardware problem. For example, it could be caused by a legacy adapter with more than one device with the same SCSI ID.
Windows 95 does not assign drive letters to tape drives and scanners because they have no drive to assign a letter to, that is, they have no official class. Therefore, they appear as Unknown Devices in Device Manager. After you start Windows 95, it asks if you have a driver for these devices. If you have Windows 95 drivers, click Yes. To use existing real-mode drivers, click No, and then type the path to where the drivers are located. Windows 95 will continue to recognize and support these devices even though they are listed as Unknown Devices.
This probably indicates that there is something wrong with the SCSI drivers in CONFIG.SYS and AUTOEXEC.BAT, or that the protected-mode SCSI drivers fail to load. Look for an IOS.LOG file and check its entries, as described in "Real-Mode Drivers and the IOS.INI Safe Driver List" earlier in this chapter.
If you type dir and strange characters appear on the screen, the hard disk might be a SCSI drive that requires double buffering which is not loaded. Verify that MSDOS.SYS has DoubleBuffer=1 in the [Options] section. (However, if you start the computer using MS-DOS version 6.0 or higher, double-buffering is provided when SMARTDRV.EXE is loaded in CONFIG.SYS.)