## Unauthorized Windows 95 Update -- RANDRW

RANDRW.C and RANDRW.EXE -- A Win32 program that determines the chances that writing to a randomly-generated pointer will or won't GP fault. There appears to be a 1-2% chance that a random pointer in Windows 95 will successfully trash memory; the chances go up for each DOS box running, because Win95 maps the four-megabyte "high linear" address space of each and every virtual machine (VM) into the address space of each and every Win32 app! RANDRW has been run under a number of different environments besides Windows 95 -- such as Win32s, Windows NT, OS/2, and Phar Lap's TNT DOS extender -- so the protection provided by the different systems can be compared.

The program generates a RANDRW.LOG file which looks like this:

    Megabyte      Attempts  Hits    % Hits
    ---------     --------  ----    ------
    00000000h	258	237	91.86
    00100000h	273	138	50.55
    00200000h	265	113	42.64
    00400000h	236	23	9.75
    00500000h	242	1	0.41
    00600000h	258	11	4.26
    80000000h	218	214	98.17
    80100000h	254	254	100.00
    80200000h	239	239	100.00
    ... etc. ...
    83900000h	207	3	1.45
    BFE00000h	268	33	12.31
    BFF00000h	262	202	77.10
    C0000000h	215	58	26.98
    C0200000h	234	128	54.70
    ... etc. ...
    C2400000h	242	242	100.00
    C2500000h	236	40	16.95
    1000000 attempts
    5991 hits
    0.60% hit rate
    519 seconds
    1926 attempts/second
    11 hits/second

The O'Reilly Windows Center

Unauthorized Windows 95 Update