🚀 go-pugleaf

eduard@htsa.aha.nl (Eduard Beijnes) writes:

>The following programs writes 2911.1971 as a serialnumber on the 
>default drive (29 nov 1971) 

>----- uuencoded program / cut here -----
>begin 600 serial.com
>4N %ILP"Z#@'-(;1,S2$  '$9$2D 
> 
>end
>----- end of uuencoded program /cut here -----

>dump van debug.com:

>2F73:0100 B80169        MOV	AX,6901                            
>2F73:0103 B300          MOV	BL,00                              
>2F73:0105 BA0E01        MOV	DX,010E                            
>2F73:0108 CD21          INT	21                                 
>2F73:010A B44C          MOV	AH,4C                              
>2F73:010C CD21          INT	21                                 
>2F73:010E 0000          ADD	[BX+SI],AL                         
>2F73:0110 7119          JNO	q012B                               
>2F73:0112 1129          ADC	[BX+DI],BP          

>I don't have the documentation with me because I am on school while
>I am writing this.

>I am not sure but if you change MOV AX,6901 in MOV AX,6900 it reads the
>serialnumber.

>If this doesn't work email me (eduard@solist.htsa.aha.nl) and I will
>look it up

You are right: 6900 returns the serial number in the disk info buffer
pointed to by DS:DX

Now my question:  I have precise detail on how the number is initially
generated.  It is a combination of date and time.  However, on a hard disk
the top two bits of the second group are set.  In theory they are beyond the
range of any combination of date and time.  Both bits may not be set.
I have seen different combinations of these bits on different systems.
Does anyone know the real mechanism for generating these two bits?

BTW, the probability of any two diskettes having the same serial number is
about 1 in 2**28, but playing around with function 6901 could lead to
identical numbers and hence a failure by MS-DOS to identify a changed
diskette (see MS-DOS User's Guide, p134)

Howie

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Howard J. Harvey                              | Email: hjh@aeg.dsto.gov.au
SOIC - Avionics Integration                   | Phone: +61 8 259 6322
Air Operations Division                       | FAX:   +61 8 259 5507
Defence Science and Technology Organisation   | c = 1802617499785.254116 f/f
Salisbury, South Australia                    |     (furlongs/fortnight)
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