There is a lot of confusion over what DASDDRVR.SYS is, what it is used for, which PS/2 models require it, and what exactly it fixes. 
The following should dispel the mystery surrounding DASDDRVR.SYS. 

What is it? 
   DASDDRVR.SYS (Direct Access Storage Device Driver) is a set of software patches that fix various BIOS bugs common to several PS/2 models.  A common misconception is that DASDDRVR.SYS is a set of DOS patches; and additionally that it is not needed with DOS 4.0x or later; only V3.3.  Both statements are incorrect. 
   IBM could have chosen to replace thousands of BIOS chips on PS/2 motherboards, yet went with the software approach.  Why? A program installs DASDDRVR.SYS on a PS/2 hard disk drive, and adds a statement to CONFIG.SYS.  Then when the system is booted, the BIOS patches overwrite the BIOS code in memory (that was copied from the BIOS ROM chips).  Not only does this give IBM and the user the flexibility of later replacing DASDDRVR.SYS with a newer version containing additional BIOS patches, if necessary; but it also eliminates the down time and inconvenience that would result from taking the system to an authorized servicer to have the BIOS ROM replaced. 

Who needs it? 
   Originally, a few BIOS bugs were found affecting several PS/2 models.  Two different versions of DASDDRVR.SYS were written, one for MCA systems, and one for non-MCA PS/2s.  As time passed, it was discovered that several more PS/2s were affected by these or newer bugs.  Eventually the two versions of DASDDRVR.SYS were merged into one, simplifying the effort of determining what to install on which systems. 
   So, to make a long story short, DOS 3.3 and later users who encounter the specific problems corrected by DASDDRVR.SYS (see below), on the particular PS/2 models listed, should install DASDDRVR.SYS.  The install program will determine which model you are installing it on, and only install those fixes that apply to that system.  (Those PS/2 models or submodels not on the list, do not need DASDDRVR.SYS, and will not benefit by installing it.) 

Why isn't DASDDRVR.SYS required on OS/2 or AIX-based PS/2s?  
   Because these operating systems routinely replace the hardware BIOS code in memory with customized software versions, anyway.  So they already contain the fixes inherent in DASDDRVR.SYS. 

What problems does it fix? 
There are currently twelve different bugs fixed.  The list below describes the fixes, and which systems are affected: 

Problems Systems Affected 
1) Failures occur when reading some 720K program floppies. 8530-E01/E21; 8550-021; 8560-041/071; 8580-041/071 
2) Intermittent "Not Ready" or "General failure" error messages when accessing diskettes. 8550-021; 8560-041/071; 8580-041/071
3) 3.5" floppy format failures when attempting to format multiple diskettes consecutively. 8550-021; 8560-041/071; 8580-041/071
4) Combined 301 and 8502 error messages at power on, or after power interruption. 8550-021; 8560-041/071
5) System clock loses time (8550), or combined 162 and 163 errors during system POST (8560). 8550-021; 8560-041/071.
6) Unable to install Power-on Password program with DASDDRVR.SYS installed.  8550-021; 8560-041/071; 8580-041/071
7) Device attached to COM2, COM3, or COM4  not detected. 8530-E01/E21
8) Devices that use interrupt request level 2 (IRQ2) fail. 8530-E01/E21
9) 3.5" floppy format failures when attempting to format >1 floppy.  8570-Axx (all); 8580-Axx (all)
10) System performance degradation from processor-intensive devices.  8550-021/031/061; 8555-031/061; 8560-041/071
11) Error in microcode routine that enhances long-term reliability of 60/120MB disk drives. 8550-061; 8555-061; 8570-061/121/A61/A21; 8573-061/121
12) Time & date errors occur when resetting time & date. Intermittent date changes can occur when system is restarted by pressing C-A-D   8530 (all)

 How do I get and install it? 
 Most versions of the various MCAl PS/2 RefDisks contain some version of DASDDRVR.SYS.  (The non-Micro Channel PS/2 Model 30 286 provides DASDDRVR.SYS on the Setup Diskette, instead.)  But because there have been several versions of DASDDRVR.SYS released along the way, with different numbers of fixes, it is important to get the latest possible version 
 of the appropriate Reference Diskette.  Depending on the version of the diskette, there may be additional fixes in a later version. 

   If you have access to the latest Reference Diskette, use it.  If not, you may call 800-IBM-7282, and request the PS/2 System Update Diskette (P/N 04G3288.  This diskette contains a version of DASDDRVR.SYS, but it is possible that by the time you read this and order it, a newer version may have been released on a new Reference Diskette.  Still, a fairly recent version is better than an older one you may have on the Reference Diskette that came with the system.  If DASDDRVR.SYS is already installed on a system, but you don't know whether it is the latest, just look at the file size.  The current version (as of July 1991) is 3,068 bytes). 
   Installation is a snap.  Simply insert the diskette in the A: drive, and type:  A:INSTALL from the C> prompt.  That's all there is to it! 
 The install program copies the DASDDRVR.SYS file to the hard disk drive, and updates CONFIG.SYS to use it.  After rebooting the system you are done. 
   One final note:  This driver may be ordered and installed by anyone.  It includes instructions, and does not require dealer  intervention. 

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