Sonic7662
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So in this situation where the computer is loading an integer into a register: Do all of the registers used in such operations have negative flags associated with them and Is the flag bit stored alongside the value in storage/memory or does it occupy a bit outside of the value? The basis of my confusion is what happens to the value of the flag when the data needs to leave the processor on a bus without a sign bit.
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I tend to have trouble with this explanation since, at the end of the day, a computer is effectively a dumb set of transistors that don't know up from down. So yes, you add a negative number to a positive number that results in a negative answer. Assuming the architecture is operating using two's complement, which I assume x86 does, let's say the result is again -1, which in an 8-bit system would be 1111 1111. The software running the computer calls for it to be stored on the hard drive, which the computer does. Then the power is turned off and on and the program now retrieves that number from the hard drive and adds it to the integer 3. 3 + -1 = 2, but the computer, if we were to look directly at the binary, would see 0000 0011 + 1111 1111, the result being 00000001 if I did my math correctly, how would the computer know if it was looking at a positive integer or a two's complement negative integers? Sorry if I sound needy or arrogant, this is just one of those things that makes me curious and I can't claim to be very experienced in this area of low-level theory. Thanks!
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I have a question I've been pondering for the longest time about two's complement negative numbers. I understand the theory behind two's compliment, you take a number, invert it and add 1 to get the negative equivalent of it for mathematical operations. This much makes sense to me and I can see the benefits of using it over signed values or one's complement. The problem I run into is what happens to the number when the computer wants to put it in memory. Suppose a subtraction operation is performed by the computer like 5 - 6, the result being negative 1. This would look like 11111111 in 8 bit binary, my question is what does the computer do when it stores this number in memory to recall that it was a negative 1 and not a 255?
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Nobody has mentioned so far that the capabilities of ARM-based processors can vary quite dramatically considering they're available to be licensed and modified design wise. Apple used to do this in many of the products that had what they called the A processors (ARM chips with 11 herbs and spices). x86 on the other hand is stuck with the instructions that it had many years ago. It's also worth pointing out that the features of both platforms can be somewhat transcending in that functionality like graphics processing can be added on alongside the processors themselves in the same die.
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I understand where you're coming from and I am completely open to the fact that I might be looking at an empty niche in the market. I just find the concept of owning one of these to be awesome and I want to try and save one from the trash and use it for something productive.
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They know how to get me now...
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I don't have my hopes up too much but they are thrown away right out of service like in this video:
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I'd like to point you to this video, a student in the US got one for $230 in nearly working order. I know it isn't exactly practical to actively look for one of these situations but I wanted to poke around and see what I can find just the same. Again, a little bit of work to bring a machine from being almost serviceable to a great toy isn't out of the question for me.
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The other problem that comes up is what I would have to do to power a mainframe. So far I haven't gotten many conclusive answers but my suspicion is that they take 3 phase at some overkill current. Not knowing much about 3 phase standards I also wonder what it would entail to set up equipment to get it.
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That's what I've come to expect, the trouble is how infrequently mainframes pop up on those sites. Would anyone know of a good place to look that maybe deals wither server old server gear and the like?
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I'm referring to one of these http://www.ebay.com/itm/IBM-2818-M05-zEnterprise-z114-zSeries-Mainframe-System-26-MIPS-8Gb-Memory-q9-/282356889165?hash=item41bdc8364d:g:SUwAAOSwdGFYnjav
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Yeah I noticed, the big difference is the use case, the X series are servers as far as I understand, while the Z series are mainframes that date back to the early computers IBM made like the System 360. If people are throwing them out I don't think people should be able to sell them used for $300k+ when many of them sold for that when they were new.
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This was the video that I was referring to when I mentioned a student in the states, there is also a guy in Switzerland who got one as well, in this case, a junk unit.
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I've seen the eBay ads, and I'm not willing to pay 15,000+ for a running/refurbished machine. I'm open to doing some work and repairing something older. A student in the states purchased a z890 for $230 and got it running SUSE with some work. I do, the particular model doesn't bother me too much and shipping is inevitable.
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I know this is an odd topic but the question is quite simple, I'm interested in getting an old IBM System Z mainframe for the fun of it and use it to bring some enrichment to the people around me who are into this kind of stuff. I've seen videos of people destructively disassembling old units because they were to be scrapped and I tend to think there are hobbyists who could get some use of them, even just to mess around with. If anyone has any ideas as to where I might look for one, leave a shout here.
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