From: Richard Lee >John W. Krahn wrote: >> Richard Lee wrote: >>> I am begining to read bit of low level(assembly) book to just gain >>> some knoweldge on inner workings of memory. >>> >>> My quesiton is, if machine is 32 bit, even if it's accessing string >>> 'A', it will have to fetch 32 bit (instead of 8 bit that requires to
>>> make that letter A ) ? >> >> It depends on the CPU. An Intel compatible CPU has instructions to >> access 8 bit values from memory but some CPUs can only access 32 bit >> aligned data. >> >>> I know this is not a mailing list for this but i figure since it's >>> closely related to pack, i thought someone would clarify for me. >> >> It is not really related to pack() as pack() is a high level function >> that can hide the details of the CPUs addressing problems. >> >>> I am reading "step by step assembly language"... I am not sure i will >>> read the whole thing but i just want to get better inner working of >>> memory as my c book didn't do enough justice. > > Just one more question on the topic, > I am trying to understand how it works in binary world. > So, If let's say I take a pcap file. I am assuming here that > ethereal/wireshark will take binaries on the wire and then decoding it > based on pcap standard(? hex? ) and then present them in ascci ? > > so which means in order to unpack pcap file, I have to know how ethereal > pack on their own.. is this something similar to what happens when pcap > file gets created? The pcap file format has a very nice solution to this problem. All data is stored in the host's native order to optimize for speed. But the file header begins with the magic number 0xa1b2c3d4. When the pcap file is read on any system, the magic number is evaluated to determine the Endean of the capture file. Then the parser knows if it needs to swap bytes as it extracts the individual packets. Bob McConnell -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] http://learn.perl.org/
