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Favorite old school hack

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  • Favorite old school hack

    What fun hacks did you pull off in the days of yore?

    Perhaps my favorite was discovering where the BIOS implementation of the keyboard ring buffer stores its data. (Segment 0x40, bytes 0x1A and 0x1C, iirc) The two values are 16-bit pointers to the head and tail pointers of the keyboard buffer. The keyboard interrupt handler routine did only one two range checks on these pointers, and that was to wrap them to the beginning when they hit the end of the buffer, and beep at you when the two pointers were one apart (indicating the buffer was full)

    This meant any system bundled with QBasic let you twiddle with these values, with a trivial program like:

    DEF SEG &H40
    POKE &H1A, 1
    POKE &H1C, 1

    Would point the buffer to an address before the pointers to the buffer themself.

    This meant that you had 25 keystrokes before the keyboard input buffer would overwrite the head pointer. After that happened, all hell broke loose, as your computer would attempt to iterate through the input buffer, but since the head pointer is corrupt it simply bounces around segment 0x40 pulling in garbage data as if it were keyboard input.

    This meant you could run the program and get it back to some sort of "normal" state as long as it took under 25 keystrokes. After that, everything would be fine for a few keystrokes, then the computer would go completely nuts.
    45 5F E1 04 22 CA 29 C4 93 3F 95 05 2B 79 2A B0
    45 5F E1 04 22 CA 29 C4 93 3F 95 05 2B 79 2A B1
    [ redacted ]

  • #2
    Re: Favorite old school hack

    Kind of a dumb little hack, but in the early/mid 90s we had purchased a newer system and kept the old. Both had modems but only one could dial out at a time.. of course networking the two via ethernet was relatively underheard of at the time and certainly not affordable to the average family (at least within the locale of our small Maine town), but IPX gaming was beginning to give folks hardons across BBSs and an emerging Internet.

    Over the prior year or so our family somehow discovered that dialing a prefix in our town allowed for a callback to be placed at your DN, on the same line... which we abused in several ways, but primarily as a paging system to whoever might be out in the garage, etc. Dail ###xxxx, where the last four digits were your local number, hang up, lift receiver, hang up then lift the receiver and wait.. ring gen would trip (by the switch?) and internal phones would ring as if receiving a call. Both parties would pick up and the call would be established. After some trial, error, and a few attempts at the terminal I was able to leverage this to establish a dialed network between our computers over the single POTS; unfortunately connectivity would only remain reliable between 2 and 5 minutes at most.

    Even with _some work in telecom, I still don't fully understand it to this day though.. /me prods around for Strom.
    if it gets me nowhere, I'll go there proud; and I'm gonna go there free.


    • #3
      Re: Favorite old school hack

      Originally posted by converge View Post
      Dail ###xxxx, where the last four digits were your local number, hang up, lift receiver, hang up then lift the receiver and wait.. ring gen would trip
      wow, i hadn't thought about that one in years. we used to do it all the time as bored teenagers at malls (with huge banks of pay phones) or at the front entrance phone of our swim club after team practices while waiting for parents to come get us.

      i can recall working as a support tech for a small computer store when i was still a teenager and using things like the 700 test or dialing 958 to identify local service numbers at customer's homes when we were trying to test out new phone lines they'd had installed (so many people would pay for a second line just for modem use and then totally bollocks up wiring in their own home) and people would just think we were some kind of sorcerers.

      heh, i can also recall one time when a guy i was working with tossed up a shell and bounced on to IRC to ask some buddies a product question (or some troubleshooting tip) and when the person whose computer it was (an elderly woman, if i recall) started to grasp that we were having a real-time conversation with people in many far-flung locales she was absolutely blown away. what could have scared a person off from computers actually wound up solidifying her appreciation for them. i think she lived alone and realized that this new device she had bought could potentially link her to new people and let her make contact with others even in solitary retirement.
      "I'll admit I had an OiNK account and frequented it quite often… What made OiNK a great place was that it was like the world's greatest record store… iTunes kind of feels like Sam Goody to me. I don't feel cool when I go there. I'm tired of seeing John Mayer's face pop up. I feel like I'm being hustled when I visit there, and I don't think their product is that great. DRM, low bit rate, etc... OiNK it existed because it filled a void of what people want."
      - Trent Reznor


      • #4
        Re: Favorite old school hack

        The hole punch on a 5.25 floppy disk to make a single density floppy a double density floppy.
        Saved lots of money back then. I think at the time I was using either a commodore 64, or a
        Tandy CoCo II.


        • #5
          Re: Favorite old school hack

          using a gender bender with a mixing and matching of 9/25 Pin Serial "Printer-only" and "Modem Only" cables to "manufacture" a "Null Modem Cable" for connecting two PCs together with stuff like the Interlink software. (Interlink cables were for parallel to parallel PC connections, and late 80's/early 90's this was a cheap way to "network" two machines for file sharing-- also, much faster than modem connections.

          Some people don't know this, but MS Windows 95 supported setting up a network between two machines with an Interlink Cable (parallel to Parallel) or Null Modem Cable (Serial to Serial) for "network neighborhood filesharing." -- Yes, once setup, you could go to network neighborhood and see the other PC you were connected to.

          Speeds ranged from 9600-to 56k to 112k for Serial, and like 100k-400k for Interlink Parallel.

          Once 1993/1994 rolled around, Ethernet was super-sheap, and you could buy NE2000- clone cards that haeb 10Base2/10BaseT so you could build a network between two MS-DOS or Windows 3.1x PCs using "cheapnet" (10Base2) for under $50.
          Of course, performance sucked, with those cheap cards. If you were lucky, you could get 50% utilization of 10Mbit.
          By 1995 the cheaper 3c509 (3com cards) were almost as cheap as the NE2000, and generally were able to approach a max of 80% utilization of a 10Mbit network on a good day.

          Now we have 10Gb "ethernet" shipping as an integrated peripheral, or 10/100/1000 Mbit in notebooks either default, or for like $20 as an upgrade during the time of purchase.

          No "good old days." Things are better now.


          • #6
            Re: Favorite old school hack

            Damn, this thread is bringing back fond memories.

            While interning in a manufacturing environment back in the day I was given a desk and began accumulating multiple systems at my desk with only ethernet connectivity for one. Out of our parts room I grabbed a blackbox 4-way printer switch with connectors for decnet (those funky little keyed rj11-like deals .. mmx? mm..?). Through some quick pinning and a few short lengths of catV I converted the switch to allow for connectivity to my multiple ethernet systems. Granted, when switched the connection would be lost on the prior box, but it was better than unplugging and reconnecting all the time ;)
            if it gets me nowhere, I'll go there proud; and I'm gonna go there free.


            • #7
              Re: Favorite old school hack

              I was in high school and we had a lab of windows animation workstations in one room and the video production in the next one over. The video stuff ran through an amiga 4000 video toaster.

              We would render the frames on the PC's but need to get them to the amiga for DV storage (before PC's could do digital video).

              School budget didn't have much for an amiga network card or other solutions (read: none) so we we had to figure out the solution on our own. We found a serial transfer package that worked on the amiga and PC through a null modem cable. We 'acquired' the use of a drill and put a hole through the wall and ran the cable through.

              couple quick commands on both ends and your animations were going at the screaming rate of 192000 baud through the line. Took all night, but it worked and was in use well after I left.
              Never drink anything larger than your head!


              • #8
                Re: Favorite old school hack

                My first hack was using a dumb terminal to connect to an Epson QX-10 at the office, running CP/M. We upgraded to a QX-16 but it would not work the same. It was some networking hack that was supposed to be impossible.


                • #9
                  Re: Favorite old school hack

                  Another couple come to mind..

                  While working at a college in Maine we were presented with an interesting problem. Our low-staffed IT department (namely me, my boss, and student workers) pretty much ran everything and anything that was fed electricity. Before a budget was created for an actual videoconferencing system, I was responsible for ducttaping together misc video components to make a functional videoconference unit. I can't remember the exact circumstances, but an upcoming video conference required a working unit, .. and I suspect it was an extension that we were after but lacked. Oh noes.. it was an oldskool 9pin graphics connector on a device that was needed!

                  Anyhow, between my friend and I... we worked out the pins for VGA, passed them through a hacked apart serial cable via splicing wizardry, and had a generally functional product at the end.

                  At the same college I became charged with designing and building a site. The attempt completely turned me off to web design altogether for the 5 or so years to follow. It was quite simple with me at the helm, but the committees of management/marketing within the school were retarded. People that do not understand the technology trying to look mighty and force their input into the project so that they could tag their name on it too. Eventually demands got so bad that I put my foot down and said 'we are doing it this way'.. at which point some of the parties got pissed off and said that they would maintain their own section of the site, causing it to lose continuity ENTIRELY, as well as general borkedness because.. as I repeat.. they had no fucking clue what they were doing.

                  I fixed this ;) My next revision of the site came in the form of a ASP driven engine. The user would browse to index.asp and be presented with what seemed to be a normal webpage. What they would soon discover was that current page was tracked by a checked GET request that fed back into the ASP and drove where that one page delivered the next set of content, organized within the public directory as a normal site would (considered DB.. but figured that was too far with my frustration). This was not designed as a good solution, but as a controlling one. By doing this I was able to dynamically change and conform ANYONES pages to meet the design needs of what I was crafting, to their stark dismay. What a fucking waste of time that was.. and no longer than 6 months or so after I left, they hired someone for $$$$$ to redesign .. basically taking the same structure I had already forged and conforming the info into a template they used for schools. Brilliance.
                  if it gets me nowhere, I'll go there proud; and I'm gonna go there free.