Update to Chapter 4

Writing a book takes years – at least it does for me. Writing a book about a computer that is still evolving is difficult. The evolution of IBM System/z machines over the last twenty years is amazing. The things I wrote years ago are often dated now – mostly correct, but dated – newer instructions, newer techniques have come along. I’ll keep working at this – editing chapters and changing the content. Today I reposted Chapter 4. Kudos to Les Kelley for some good suggestions that got me thinking.

8 thoughts on “Update to Chapter 4”

  1. I have only just started to go through this..I’m sure I’ll have more comments !

    Chapter 1…This is entirely academic, but let’s split IBM Assembler into two pieces. There is what we now know as HLASM, and then there is the instruction set

    The IBM/360 instruction set did indeed start in October 1964, but the Assembler existed much earlier with the IBM 1400 series

    Do these look familiar…
    DC DS ORG LTORG EQU *(as location)
    All of these were in use in 1401 Autocoder, around 10 years before IBM 360


  2. Hi,

    Chapter 2 Paragraph 2 states:

    This has increased from the original 24 to 31 and finally 64 bits.

    I believe that the word “finally” should be changed to “currently”, since 64 bits might not be the end.

  3. Hi,

    First, page numbers are missing on this chapter.

    Chapter 3 begins with “In Appendix A, we created a small program with the editor, submitted it for execution, and examined the results. We’ll revisit that program in this chapter, examine its parts, and try to get the lay of the land. We’ll concentrate on how to organize a simple assembler program. It’s time to jump in.”

    Isn’t it sort of confusing to tell someone just beginning and about to create their first program, to be told that they should have skipped to appendix A (which they won’t understand based on what they have been taught so far)? It would be far better (I think) to rephrase the paragraph so that it might still mention that they will process this same “first program” in appendix “A” which they can reference for examples. Otherwise they will start out this chapter already depressed that they missed something and that the techniques might be beyond their ability to learn.

    “n our case, that’s the family of System/z machines. IBM assembly language – HLASM (High-Level Assembler) – won’t run on an Intel or Mac OS box.”

    Is sort of a very confusing run-on sentence. I think the sentence should end with “HLASM (High Level Assembler) and then a new sentence should start with “It won’t run on an Intel or Mac OS Box.”

    As a side note, that statement is not really entirely true, because the person could run Hercules on their PC (mac or PC), and run MVS under that, or they could run the OS/380 emulator, which would allow them to execute it. Maybe those products should have been mentioned up in Chapter 2.

    The code below:

    I think this is just an oversight, but it should be shifted to the right in the box instead of lining up on the left. People will assume that they are supposed to write the code in column 1 (as you have shown) when to needs to be started after column ‘1’. Strangely, the “LOOP” and “GET” is lined up correctly, while the rest is misaligned.

    The chart on the next page needs to say something about the continuation column and it probably needs to be identified as such on the chart, otherwise they will think they are comments or that they just need to randomly put an “X” to continue a line:

    You need to use color in the pictures if you are going to talk about colors.

    Personally I am colorblind, so the actual colors would not have meant anything to me, but I can tell when there aren’t any. 😊


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