SCSI and DISK386.SYS

SCSI and DISK386.SYS
IBM Announcement Letter Section on DISK386.SYS and INSTDBUF.COM


SCSI and DISK386.SYS

Source: Personal Systems/Issue 4, 1990 (G325-5009-00), Page 36 physical

This is a description of the Update Program Driver, DISK386.SYS, for IBM SCSI adapters. This program should be installed only if the user is experiencing problems, and only after considering the performance implications.

The IBM PS/2 Micro Channel SCSI adapters announced by IBM on March 20, 1990, are bus master adapters. Because bus master adapters read and write data directly to or from system memory, they do not use the Direct Memory Access (DMA) controller on the system board. This increases performance by allowing the system processor to perform other tasks while the SCSI bus master adapter transfers data.

The Update Program driver is provided in order to maintain compatibility with certain multitasking DOS applications or memory extenders that assume the fixed-disk drive will use the system DMA controller. When this driver is installed, it reserves a buffer in the first megabyte of system memory that serves as an intermediate location for data being transferred between the SCSI adapter and the requesting application’s buffer. While the driver allows you to run applications that assume the fixed-disk drive will use the system DMA controller, it may cause some performance degradation in file access time.

The Update Program driver should only be installed when applications providing DOS memory extensions fail to work properly when used with a PS/2 SCSI adapter. For example, an application may fail to load and return the user to the DOS prompt; or when attempting to access a SCSI device, the system may "hang" or the screen may go blank.

Specific examples of applications that do not need the Update Program driver are Windows 3.0, DESQview 386 with QEMM 5.0, 386 MAX 4.08, 386 Professional 4.08, and VM/386. Older versions of these applications, and or expanded memory under DOS, may need the Update Program driver installed in order to operate properly.

IBM recommends that users update their applications to maximize overall system performance rather than install the Update Program driver. However, this program is made available to provide the option of maintaining compatibility with previously purchased applications.

These instructions also apply to the generic Update Program driver, GENS386.SYS, supplied on the option disks shipped with non-fixed disk SCSI options such as the IBM PS/2 CD-ROM Drive.

The following documents, which are shipped with the products, include instructions for the installation of DISK386.SYS:

  • IBM PS/2 Micro Channel SCSI Adapter w/ Cache Installation Instructions (page 12)
  • IBM PS/2 Micro Channel SCSI Adapter Installation Instructions (page 10)
  • IBM PS/2 Model 65 SX Quick Reference (page 74)
  • IBM PS/2 Model 80 Quick Reference (page 82)


IBM Announcement Letter - DISK386.SYS and INSTDBUF.COM

DISK386.SYS maintains compatibility between SCSI devices, IBM DOS, and some of the following types of programs that assume the fixed disk drive will utilize the system Direct Memory Access (DMA) controller:

  • Multitasking DOS programs
  • Programs written for the 80386 microprocessor only
  • Programs that use the virtual 8086 mode of the 80386 microprocessor
  • Programs that emulate expanded memory specification (EMS) in extended memory

DISK386.SYS should only be installed when applications providing DOS and/or memory extensions fail to work properly. For example, an application may fail to load and return the DOS prompt or when attempting to access a SCSI device, the system may hang or the screen may go blank.

When DISK386.SYS is installed, a buffer is provided in the first megabyte of system memory that serves as an intermediate location for data transferred between the SCSI adapter and the requesting program's buffer. While this update program allows applications that utilize the system DMA controller to run, some performance degradation in file access time may be experienced. Only after problems have been experienced, and the performance implications considered, should this update program be utilized.

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