275 lines
8.5 KiB
Plaintext
275 lines
8.5 KiB
Plaintext
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****************************************
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* B U C K A R O O B A N Z A I *
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* aka the Reset Vector *
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* *
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* presents *
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* *
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* Cracking On the IBMpc *
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* Part I *
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* *
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****************************************
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Introduction
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------------
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For years, I have seen cracking
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tutorials for the APPLE computers, but
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never have I seen one for the PC. I
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have decided to try to write this series
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to help that pirate move up a level to a
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crackest.
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In this part, I will cover what
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happens with INT 13 and how most copy
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protection schemes will use it. I
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strongly suggest a knowledge of
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Assembler (M/L) and how to use DEBUG.
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These will be an important figure in
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cracking anything.
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INT-13 - An overview
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--------------------
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Many copy protection schemes use the
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disk interrupt (INT-13). INT-13 is
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often use to either try to read in a
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illegaly formated track/sector or to
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write/format a track/sector that has
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been damaged in some way.
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INT-13 is called like any normal
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interupt with the assembler command
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INT 13 (CD 13). [AH] is used to select
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which command to be used, with most of
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the other registers used for data.
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INT-13 Cracking Collage
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-----------------------
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Although, INT-13 is used in almost all
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protection schemes, the easiest to crack
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is the DOS file. Now the protected
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program might use INT-13 to load some
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other data from a normal track/sector on
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a disk, so it is important to determine
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which tracks/sectors are inportant to
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the protection scheme. I have found the
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best way to do this is to use
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LOCKSMITH/pc (what, you don't have LS.
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Contact your local pirate for it.)
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Use LS to to analyze the diskette.
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Write down any track/sector that seems
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abnormal. These track are must likely
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are part of the protection routine.
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Now, we must enter debug. Load in the
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file execute a search for CD 13. Record
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any address show. If no address are
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picked up, this mean 1 or 2 things, the
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program is not copy protected (bullshit)
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or that the check is in an other part of
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the program not yet loaded. The latter
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being a real bitch to find, so I'll
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cover it in part II. There is another
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choice. The CD 13 might be hidden in
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self changing code. Here is what a
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sector of hidden code might look like
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-U CS:0000
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1B00:0000 31DB XOR BX,BX
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1B00:0002 8EDB MOV DS,BX
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1B00:0004 BB0D00 MOV BX,000D
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1B00:0007 8A07 MOV AL,[BX]
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1B00:0009 3412 XOR AL,12
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1B00:000B 8807 MOV [BX],AL
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1B00:000D DF13 FIST WORD...
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In this section of code, [AL] is set
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to DF at location 1B00:0007. When you
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XOR DF and 12, you would get a CD(hex)
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for the INT opcode which is placed right
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next to a 13 ie, giving you CD13 or INT-
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13. This type of code cann't and will
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not be found using debug's [S]earch
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command.
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Finding Hidden INT-13s
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----------------------
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The way I find best to find hidden
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INT-13s, is to use a program called
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PC-WATCH (TRAP13 works well also). This
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program traps the interrupts and will
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print where they were called from. Once
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running this, you can just disassemble
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around the address until you find code
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that look like it is setting up the disk
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interupt.
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An other way to decode the INT-13 is
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to use debug's [G]o command. Just set a
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breakpoint at the address give by
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PC-WATCH (both programs give the return
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address). Ie, -G CS:000F (see code
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above). When debug stops, you will have
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encoded not only the INT-13 but anything
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else leading up to it.
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What to do once you find INT-13
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-------------------------------
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Once you find the INT-13, the hard
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part for the most part is over. All
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that is left to do is to fool the
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computer in to thinking the protection
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has been found. To find out what the
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computer is looking for, examine the
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code right after the INT-13. Look for
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any branches having to do with the CARRY
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FLAG or any CMP to the AH register.
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If a JNE or JC (etc) occurs, then
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[U]nassembe the address listed with the
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jump. If it is a CMP then just read on.
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Here you must decide if the program
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was looking for a protected track or
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just a normal track. If it has a
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CMP AH,0 and it has read in a protected
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track, it can be assumed that it was
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looking to see if the program had
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successfully complete the READ/FORMAT of
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that track and that the disk had been
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copied thus JMPing back to DOS
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(usually). If this is the case, Just
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NOP the bytes for the CMP and the
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corrisponding JMP.
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If the program just checked for the
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carry flag to be set, and it isn't, then
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the program usually assumes that the
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disk has been copied. Examine the
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following code
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INT 13 <-- Read in the Sector
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JC 1B00 <-- Protection found
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INT 19 <-- Reboot
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1B00 (rest of program)
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The program carries out the INT and
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find an error (the illegaly formatted
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sector) so the carry flag is set. The
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computer, at the next instruction, see
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that the carry flag is set and know that
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the protection has not been breached.
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In this case, to fool the computer, just
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change the "JC 1B00" to a "JMP 1B00"
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thus defeating the protection scheme.
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NOTE: the PROTECTION ROUTINE might be
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found in more than just 1 part of
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the program
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Handling EXE files
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------------------
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As we all know, Debug can read .EXE
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files but cannot write them. To get
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around this, load and go about cracking
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the program as usual. When the
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protection scheme has been found and
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tested, record (use the debug [D]ump
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command) to save + & - 10 bytes of the
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code around the INT 13.
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Exit back to dos and rename the file
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to a .ZAP (any extention but .EXE will
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do) and reloading with debug.
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Search the program for the 20+ bytes
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surrounding the code and record the
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address found. Then just load this
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section and edit it like normal.
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Save the file and exit back to dos.
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Rename it back to the .EXE file and it
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should be cracked. ***NOTE: Sometimes
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you have to fuck around for a while to
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make it work.
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DISK I/O (INT-13)
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-----------------
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This interrupt uses the AH resister to
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select the function to be used. Here is
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a chart describing the interrupt.
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AH=0 Reset Disk
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AH=1 Read the Status of the Disk
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system in to AL
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AL Error
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----------------------------
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00 - Successful
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01 - Bad command given to INT
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*02 - Address mark not found
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03 - write attempted on write prot
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*04 - request sector not found
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08 - DMA overrun
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09 - attempt to cross DMA boundry
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*10 - bad CRC on disk read
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20 - controller has failed
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40 - seek operation failed
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80 - attachment failed
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(* denotes most used in copy protection)
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AH=2 Read Sectors
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input
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DL = Drive number (0-3)
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DH = Head number (0or1)
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CH = Track number
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CL = Sector number
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AL = # of sectors to read
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ES:BX = load address
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output
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AH =error number (see above)
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[Carry Flag Set]
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AL = # of sectors read
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AH=3 Write (params. as above)
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AH=4 Verify (params. as above -ES:BX)
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AH=5 Format (params. as above -CL,AL
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ES:BX points to format
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Table)
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For more infomation on INT-13 see the
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IBM Techinal Reference Manuals.
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Comming Soon
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------------
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In part II, I will cover CALLs to
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INT-13 and INT-13 that is located in
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diffrents overlays of the program
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Happy Cracking.....
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Buckaroo Banzai
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<-------+------->
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PS: This Phile can be Upload in it's
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unmodified FORM ONLY.
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PPS: Any suggestion, corrections,
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comment on this Phile are accepted and
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incouraged.....
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[0m
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Acquired from FCP II..
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Hit a key..
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X-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-X
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Another file downloaded from: The NIRVANAnet(tm) Seven
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& the Temple of the Screaming Electron Taipan Enigma 510/935-5845
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Burn This Flag Zardoz 408/363-9766
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realitycheck Poindexter Fortran 510/527-1662
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Lies Unlimited Mick Freen 801/278-2699
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The New Dork Sublime Biffnix 415/864-DORK
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The Shrine Rif Raf 206/794-6674
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Planet Mirth Simon Jester 510/786-6560
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"Raw Data for Raw Nerves"
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X-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-X
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