piatok: tip na knihu

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kupil som si knihu Hackers: Heroes of the Computer Revolution (by Steven 
Levy)
http://en.wikipedia.org/wiki/Hackers_Heroes_of_the_Computer_Revolution
Mozem doporucit, je to naozaj vyzivne citanie. Prikladam malu vzorovu 
kapitolu o pridavani instrukcie do pocitaca. Velmi dobre som sa na tom 
pobavil :-)



Nelson thought that adding an "add to memory" instruction would improve 
the machine. It would take months, perhaps, to go through channels to do 
it, and if he did it himself he would learn something about the way the 
world worked. So one night Stewart Nelson spontaneously convened the 
Midnight Computer Wiring Society. This was an entirely ad hoc 
organization which would, when the flow of history required it, 
circumvent the regulations of the Massachusetts Institute of Technology 
against unauthorized tampering with expensive computers. The MCWS, which 
that night consisted of Nelson, a student worker, and several interested 
bystanders, opened up the cabinet and proceeded to rewire the PDP-1. 
Nelson fused a couple of diodes between the "add" line and the "store" 
line outputs of the instruction decoder, and had himself a new op-code, 
which presumably supported all the previous instructions. He then 
proceeded to reassemble the machine to an apparent pristine state.
The machine was taken through its paces by the hackers that night, and 
worked fine. But the next day an Officially Sanctioned User named 
Margaret Hamilton
showed up on the ninth floor to work on something called a Vortex Model 
for a weather-simulation project she was working on. Margaret Hamilton 
was just beginning a programming career which would see her eventually 
in charge of on- board computers on the Apollo moon shot, and the Vortex 
program at that time was a very big program for her. She was well aware 
of the hackers' playfulness around the ninth floor, and she was 
moderately friendly with some of them, even though they would eventually 
blend into one collective personality in her memory: one unkempt, though 
polite, young male whose love for the computer had made him lose all reason.
The assembler that Margaret Hamilton used with her Vortex program was 
not the hacker-written MIDAS assembler, but the DEC-supplied DECAL 
system that the hackers considered absolutely horrid. So of course 
Nelson and the MCWS, when testing the machine the previous night, had 
not used the DECAL assembler. They had never even considered the 
possibility that the DECAL assembler accessed the instruction code in a 
different manner than MIDAS, a manner that was affected to a greater 
degree by the slight forward voltage drop created by the addition of two 
diodes between the add line and the store line. Margaret Hamilton, of 
course, was unaware that the PDP-1 had undergone surgery the previous 
night. So she did not immediately know the reason why her Vortex 
program, after she fed it in with the DECAL assembler ... broke. Stopped 
working. Died. Mysteriously, a perfectly good program had bombed. Though 
programs often did that for various reasons, this time Margaret Hamilton 
complained about it, and someone looked into why, and someone else 
fingered the Midnight Computer Wiring Society. So there were 
repercussions. Reprimands.
That was not the end of the Midnight Computer Wiring Society. Edwards 
and his ilk could not stay up all night to watch the machines. Besides, 
Minsky and the others in charge of Project MAC knew that the hackers' 
nocturnal activities were turning into a hands-on postgraduate course on 
logic design and hardware skills. Partially because Nelson and the 
others got good enough so disasters like the Great Margaret Hamilton 
Program Clobber were less likely to occur, the official AI lab ban 
against hardware tampering gradually faded away to the status of one of 
those antiquated laws that nobody bothers to take off the books, like a 
statute forbidding you from publicly beating a horse on Sunday. 
Eventually the Midnight Computer Wiring Society felt free enough to 
change instructions, make new hardware connections, and even rig the 
computer to the room lights on the ninth floor, so that when you fired 
up the TECO text-editing program, the lights automatically dimmed so 
that you could read the CRT display more easily.
This last hack had an unexpected consequence. The TECO editor rang a 
bell on the teletype to signal when the user made an error. This 
normally was no problem, but on certain days the machine got flaky, and 
was extremely sensitive to power line
variations like those generated by the bell on the teletype. Those 
times, when someone made a mistake with TECO, the bell would ring, and 
the machine would be thrown into randomness. The computer would be out 
of control; it would type spastically, ringing the bell, and most 
unsettling, turning the room lights on and off. The computer had run 
amok! Science-fiction Armageddon! The hackers considered this extremely 
humorous. The people in charge of the lab, particularly Marvin Minsky, 
were very understanding about these things. Marvin, as the hackers 
called him (they invariably called each other by last name), knew that 
the Hacker Ethic was what kept the lab productive, and he was not going 
to tamper with one of the crucial components of hackerism. On the other 
hand, there was Stew Nelson, constantly at odds with the rules, a hot 
potato who got hotter when he was eventually caught red-handed at phone 
hacking. Something had to be done. So Minsky called up his good friend 
Ed Fredkin, and told him he had this problem with an incredibly 
brilliant nineteen-year old who had a penchant for getting into 
sophisticated mischief. Could Fredkin hire him?