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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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