8 x 1019 bytes 18 eb exabytes x8664 supports 48bit

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Unformatted text preview: gram can clobber its own data, but not that of others Clobbering code or “state” ogen leads to crashes (or security holes) Compiler + run ­Jme system control memory allocaJon   Where different program objects should be stored   All allocaGon within a single address space Memory 13 University of Washington Machine Words   Machine has a “word size”   Nominal size of integer ­valued data Including addresses   UnGl recently, most machines used 32 bits (4 bytes) words   Limits addresses to 4GB   Became too small for memory ­intensive applicaGons   More recent and high ­end systems use 64 bits (8 bytes) words   PotenGal address space ≈ 1.8 X 1019 bytes (18 EB – exabytes)   x86 ­64 supports 48 ­bit physical addresses: 256 TB (terabytes)   For backward ­compaGbility, many CPUs support different word sizes   Always a power ­of ­2 in the number of bytes: 1, 2, 4, 8, …   Memory 14 University of Washington Word ­Oriented Memory OrganizaJon   Addresses specify locaJons of bytes in memory 64 ­bit Words   Address of first byte in word   Addresses of successive words differ by 4 (32 ­bit) or 8 (64 ­bit)   Address of word 0, 1, .. 10? Addr = ?? Addr = ?? 32 ­bit Words Addr = ?? Addr = ?? Addr = ?? Addr = ?? Memory Bytes Addr. 0000 0001 0002 0003 0004 0005 0006 0007 0008 0009 0010 0011 0012 0013 0014 0015 15 University of Washington Word ­Oriented Memory OrganizaJon   Addresses specify locaJons of bytes in memory 64 ­bit Words   Address of first byte in word   Addresses of successive words differ by 4 (32 ­bit) or 8 (64 ­bit)   Address of word 0, 1, .. 10? Addr = 0000 ?? Addr = 0008 ?? 32 ­bit Words Addr = 0000 ?? Addr = 0004 ?? Addr = 0008 ?? Addr = 0012 ?? Memory Bytes Addr. 0000 0001 0002 0003 0004 0005 0006 0007 0008 0009 0010 0011 0012 0013 0014 0015 16 University of Washington Memory, Data, and Addressing           Preliminaries RepresenJng informaJon as bits and bytes Organizing and addressing data in memory ManipulaJng data in memory...
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