ID Number: Q65469
2.00
OS/2
Summary:
The file BASEDDnn.SYS, where "nn" is 01 for ISA and EISA (non-ABIOS)
machines, and 02 for PS/2 MCA (ABIOS) machines, is located in the root
directory of the primary partition. This file is the default driver
file for the clock, screen, disk driver, etc., and is limited to a 64K
file size. Adding specific device drivers such as DISKnn.SYS,
KBDnn.SYS, etc., allows you to work around the 64K file size limit,
and also adds functionality that is missing in BASEDDnn.SYS. These
files are also placed in the root directory.
OS/2 LAN Manager version 2.00 offers to install a DISKnn.SYS file to
add functions that are not supported in BASEDDnn.SYS. The DISKnn.SYS
file is part of OS/2 and is not on the OS/2 LAN Manager disks. Compaq
OS/2 version 1.21 automatically installs this file during its
installation and then OS/2 LAN Manager does not also need to install
this file. The OS/2 LAN Manager setup program will, however, still
offer to install this file.
Two important functions in DISKnn.SYS used by OS/2 LAN Manager are
fault tolerance and a disk read/write technique called "scatter
gather." DISKnn.SYS supports fault tolerance when it is enabled with
some ring 3 utilities and interfaces to the DISKFT.SYS driver.
HPFS386, the file system packaged with OS/2 LAN Manager, uses the
enhanced device driver interface called "scatter gather." This
interface allows multiple requests to be chained together and passed
to the driver all at once, which saves the overhead of calling the
driver multiple times.
In addition, within each request, there is the capability to specify a
list of separate memory areas to be used for the target of the read or
write operation. Together, the list of memory areas and the multiple
requests allow the file system to pass a single packet to the device
driver that handles discontiguity on the disk media, and discontiguity
in memory.
HPFS386 does not require that this interface to the disk driver be
supported, rather it will use it if it is there. HPFS386 will function
without the use of DISKnn.SYS. OS/2 LAN Manager also functions without
DISKnn.SYS but will use the extra functionality if it is installed.