Tue Oct 27 - context, some bits & bytes, some machine code

I have to leave at 3pm today. I can meet later tonight, say 8pm, with anyone who has more questions or want's to talk about anything.

Questions ?

context

• What are the conceptual (and real) parts of a computer?
• What is a "process" ? What is the "operating system" ?
• top command
• Discuss how the system manages processes :
  • memory (real & virtual)
  • instruction codes & data ... all have addresses
• We want to look at the details ... which is why we're starting with data.

bits & bytes

• ints & strings in memory : CMU bits & bytes 1, pg 51) - memory
• review signed vs unsigned : pg 20
• floating point : CMU float ... I'm not going to emphasize this stuff. Worth knowing the basics.

some C

int a[5] = {10, 11, 12, 13, 14}; // NOTE : can only use {} in declarations.
int c[5];
int* b;

printf(" a is %p \n", a);
printf(" &a[0] is %p \n", &a[0]);
printf(" a[0] is %d \n", a[0]);
printf(" *a is %d \n", *a);

printf(" c[0] is %d \n", c[0]);   // What will this do?
printf(" *b is %d \n", *b);       // what will this do?


c[0] = 100;      // Is this OK?  (Yes.)
*(c+1) = 200;    // What the heck is this ? (It's c[1] ... at what address?)

*b = 20;         // Is this OK?  (NO!!!)

b = malloc(200 * sizeof(int));     // memory allocate - "the heap" - runtime

Discuss ...

• pointers
• arrays
• stack | function calls | compile time declarations
• heap | run time memory allocation : malloc, calloc

HW1 assignment

Due today.

For all of these homework exercises, use your own judgement as to how much to do and where to spend your time.

I'm trying to choose work that will help you understand the material. If it it's too much, do what you can; if it comes easily, do more. ;)

I've posted my answers that you can compare with your own or look for hints if you're stuck.

Next

On Thursday I'll start in with the stuff in "machine prog" CMU lecture notes; therere are 4 of them (basics, control, procedures, data) that we'll want to have a handle on to do the bomb lab, one week from Friday.

Also by Thursday I'll have some exercises for next Tues night posted.

aside

How much memory is a kilobyte really? A thousand bytes? Or do people mean 2*10 = 1024. How about a megabyte? Hmmm.

• kibibyte (2**10)
• mebibyte (2**20)
• gibibyte (2**30)

Quick quiz :

• How much memory can you address with a 32 bit pointer ? (answer: 4GB)
• a 64 bit pointer ? (answer: eighteen million terabytes ...)

Another quick quiz :

• What is Mbps mean for bandwidth?

powers of 2 to "just know"
-------------------
  2**6  = 64
  2**8  = 256 (one byte)
  2**10 = 1024