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I've been reading how memory works from a book. The problem is my weak english so I can't catch the meaning correctly.

The text from the book :

A computer with a 32-bit word has 4 bytes/word, whereas acomputer with a 64-bit word has 8 bytes/word. The significance of aword is that most instructions operate on entire words, for example, adding two wordstogether. Thus a32-bit machine will have 32-bit registers and instructions for manipulating 32-bit words, whereas a 64-bit machine will have 64-bit registers and instructions for moving, adding, subtracting, and otherwise manipulating 64-bit words.

Before you laugh, I will show my interpretation of the text. The diagram is extracted from the book. Its for 32 bit case. enter image description here

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Your interpretation is correct.

In terms of the line:

"the total is 4 words x 4 bytes = 16 bytes which is 128 bits"

That is the total size of the memory. Each word in that memory is 32 bits, and you have 4 of them giving a total size of 128 bits.

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  • \$\begingroup\$ That is for one specific architecture for which those numbers match, including one byte being 8 bits \$\endgroup\$ – PlasmaHH Jun 26 '16 at 21:06
  • \$\begingroup\$ My God what wasted hours understanding this. Thank you very much you're hell fast understanding my problem. Genius! \$\endgroup\$ – Plain_Dude_Sleeping_Alone Jun 26 '16 at 21:13
  • \$\begingroup\$ Btw, so that 32 bits is refering to a word. So if I say I have 32 bit memory means its 32 bits per word? \$\endgroup\$ – Plain_Dude_Sleeping_Alone Jun 26 '16 at 21:16
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    \$\begingroup\$ @Hey-men-whatsup correct. \$\endgroup\$ – Tom Carpenter Jun 26 '16 at 21:17
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enter image description here

Figure 1. Windows Caculator in Programmer mode. (Menu: View | Programmer.)

You may find your Windows (or whatever OS you use) calculator helpful in this regard. Calc makes the distinction clear by using Word for 16-bit, Dword (double) for 32-bit and Qword (quad) for 64-bit.

In the screengrab shown in Figure 1 I have selected Qword (4 x 16-bit = 64-bit) and typed in a hexadecimal number. Here we can see that each hex digit uses a nibble (4-bits): 1 = 0001, 2 = 0010, etc., with all 16 characters using 64 bits.

You may find it instructive to start with Byte mode and Hex or Dec display and start adding numbers (including some negative numbers) to see how it works. When you've got that then go to Word, Dword, etc.

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  • \$\begingroup\$ Thank you your answer also important for me in the future. \$\endgroup\$ – Plain_Dude_Sleeping_Alone Jun 26 '16 at 21:28
  • \$\begingroup\$ Not to be picky big guy, but your showing "Word for 16-bit, Dword (double) for 16-bit and Qword (quad) for 32-bit." Should a Dword be 32 bits and a Qword be 64 bits? Occasional typo's are forgiven. \$\endgroup\$ – Sparky256 Jun 26 '16 at 21:33
  • \$\begingroup\$ Ha! What happens if the typos get more regular? Thanks for the tip-off. \$\endgroup\$ – Transistor Jun 26 '16 at 22:31

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