Lecture 7/12: Storing Numbers in Memory and Byte Ordering

Prof. Harry Porter
Portland State University
cs.pdx.edu/~harry

[@tcmata11]

Great videos. Drawn out figures make it much easier to comprehend. Learned more in these 15 minutes, than I have in 3 hours in my assembly language lecture

[@bik8353]

Mr. Harry Potter does his magic once again. Thank you SO much

[@MulleDK19]

From a technical standpoint, little endian makes the most sense. It ensures that no matter the size of the value, the least significant byte, is always the same address. So eg. accessing a value as a short or a byte will access the same address, not having to offset. B = Big endian L = Little endian 0 1 2 3 B: 00 00 00 FF

[@karthikbahaddurgattematha4651]

I loved her... very good .... with a good example... thanks a lot

[@COMB0RICO]

Excellent teaching! Thanks from Texas.

[@hariboi991]

This helped tons! Thanks a lot for the clear explanations and nice examples!

[@TheDuckofDoom.]

Small definition-accuracy issue, the meaning and length of a "word" varies with the operating system, machine architecture, and programming language. Some use 2-bytes as the definition(and the bits per byte can depend on the machine, a few have used 9 or 12bit bytes over the years) others use the max atomic capacity of the CPU eg 64bits on a 64bit CPU. x86 assembly still uses 16bits due to the 16bit 8086 and 80286 origin of the x86[_64] instruction set.

[@chuckdudley]

exactly - thank you

[@guliyevshahriyar]

Thank you very much

[@johntabor2619]

Thanks for sharing

[@vineeshcv]

Thanks for the explanation, this is really good explanation about endianess

[@anondoggo]

Sorry if I'm wrong, but I think in the examples, the addresses used to store the data are not aligned? (just wanted to check my concept, thank you!

[@LeeHongYee99]

Very good lecture, more people should view.

[@문창민-f2k]

16:30 Why characters have a same output? ㅡㅡ I see now. Endian is matter about a data type like int, word etc, not a combination of data type. So a single char is endianness.

[@mehrdadkiani8476]

I wish I was one of your students, Professor Harry Porter.

[@roschoandrew5440]

Very good explanations there.

[@Zeropadd]

💖

[@lnsights]

nice lecture......easy to understand

[@laoying20]

Hello Prof. Harry Porter, good day thanks for your video. it helped me a lot. I want to know everything about computer Memory & CPU. can you please introduce me a book or any other resources? Appreciate a lot.

[@billmichae]

Double Word is called LONG WORD

[@ShabaazShaikz]

Good information

[@hadeseye2297]

I can't agree with you on the word size. It's architecture dependant. For 8 bit cpus its width is 8 bits. Other than that, nice you use C. This way people can look into memory, rather than rely on runtime environment and words of the authors of books, or tutorials.

[@blank336]

Would be great if someone can clarify if I understood this least sig byte & most sig byte correctly; for example given in the video, 32-bit Integer value is 0x01234567 with big-endian being 01 23 45 67 and little-endian being 67 45 23 01. If the 32-bit Integer value happened to be 0x87654321 instead, would the big-endian be 87 65 43 21 and little-endian being 21 43 65 87? Thanks in advance.

[@billmichae]

Half Byte is a Nibble

[@kingnehmna7810]

thank you

[@catlord69]

pretty sure "sizeof" function is in standard library

[@hhp3]

Actually, “sizeof” is built directly in to the C and C++ languages. It is a unary operator, like + and - . It is not a function, and it not included from a library. For example, you can say “sizeof buffer” although most programmers write “sizeof ( buffer )” instead. Note that you can’t leave off the parentheses for normal functions, so “foo ( buffer )” cannot be written as “foo buffer”.

[@yank3656]

thanks for sharing hhp3

[@Manoj_1102]

Please correct it , Word contain 16 bits (2 Byte) while Dword contain 32 bits (4 byte) and so on...

[@CR-um6bb]

What is the 0x for??

[@blank336]

I believe its a C format for saying that its hexadecimal. Not sure if this definition is correct, just from an unstable memory of a dude that started learning :)

[@giuseppeatanasio2926]

0x means Hexadecimal. So, every character before the 0x is an hexadecimal number

[@idafeoghene6984]

I thought a WORD is 16bits

[@rickicalder9267]

Correct according to Intel and most electrical engineering courses a Word is exactly 16 bits. cse.unl.edu/~goddard/Courses/CSCE351/IntelArchitecture/IntelDataType.pdf

[@japhethobala3753]

It depends with the architecture of the machine. The bit-iness of the cpu defines how many bits exists in a word this is because the CPU operates on a word. So a 16 bit machine has words of size 16 bits, a 32 bit machine has words of size 32 bits so on and so forth.

[@AlqGo]

&ip is a pointer to a pointer but it matters not for the purpose of your video