{"id":1669,"date":"2017-02-10T14:35:07","date_gmt":"2017-02-10T19:35:07","guid":{"rendered":"http:\/\/jungwon.kim\/blog\/?p=1669"},"modified":"2017-02-10T14:35:07","modified_gmt":"2017-02-10T19:35:07","slug":"64-bit-computing-limits-of-practical-processors","status":"publish","type":"post","link":"https:\/\/blog.jungwon.kim\/?p=1669","title":{"rendered":"64-bit computing Limits of practical processors"},"content":{"rendered":"<p><a href=\"https:\/\/en.wikipedia.org\/wiki\/64-bit_computing\">https:\/\/en.wikipedia.org\/wiki\/64-bit_computing<\/a><\/p>\n<p>In principle, a 64-bit microprocessor can address 16\u00c2\u00a0<a title=\"Exbibyte\" href=\"https:\/\/en.wikipedia.org\/wiki\/Exbibyte\">EiBs<\/a> (<span class=\"nowrap\">16 \u00c3\u2014 1024<sup>6<\/sup> = 2<sup>64<\/sup> = 18,446,744,073,709,551,616 bytes<\/span>, or about 18.1\u00c2\u00a0exabytes) of memory. In actual practice, it is orders of magnitudes less than that.<\/p>\n<p>For example, the <a title=\"X86-64\" href=\"https:\/\/en.wikipedia.org\/wiki\/X86-64\">AMD64 architecture<\/a> (as of 2011) allows 52\u00c2\u00a0bits for physical memory and 48 bits for virtual memory.<sup id=\"cite_ref-8\" class=\"reference\"><a href=\"https:\/\/en.wikipedia.org\/wiki\/64-bit_computing#cite_note-8\">[8]<\/a><\/sup> These limits allow memory sizes of 4\u00c2\u00a0<a title=\"Pebibyte\" href=\"https:\/\/en.wikipedia.org\/wiki\/Pebibyte\">PiB<\/a> (<span class=\"nowrap\">4 \u00c3\u2014 1024<sup>5<\/sup> bytes<\/span>) and 256\u00c2\u00a0<a title=\"Tebibyte\" href=\"https:\/\/en.wikipedia.org\/wiki\/Tebibyte\">TiB<\/a> (<span class=\"nowrap\">256 \u00c3\u2014 1024<sup>4<\/sup> bytes<\/span>), respectively. A PC cannot currently contain 4\u00c2\u00a0pebibytes of memory (due to the physical size of the memory chips), but AMD envisioned large servers, shared memory clusters, and other uses of physical address space that might approach this in the foreseeable future. Thus the 52-bit physical address provides ample room for expansion while not incurring the cost of implementing full 64-bit physical addresses. Similarly, the 48-bit virtual address space was designed to provide more than 65,000 (2<sup>16<\/sup>) times the 32-bit limit of 4\u00c2\u00a0GiB (<span class=\"nowrap\">4 \u00c3\u2014 1024<sup>3<\/sup> bytes<\/span>), allowing room for later expansion and incurring no overhead of translating full 64-bit addresses.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>https:\/\/en.wikipedia.org\/wiki\/64-bit_computing In principle, a 64-bit microprocessor can address 16\u00c2\u00a0EiBs (16 \u00c3\u2014 10246 = 264 = 18,446,744,073,709,551,616 bytes, or about 18.1\u00c2\u00a0exabytes) of memory. In actual practice, it is orders of magnitudes less than that. For example, the AMD64 architecture (as of<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[],"class_list":["post-1669","post","type-post","status-publish","format-standard","hentry","category-cs"],"_links":{"self":[{"href":"https:\/\/blog.jungwon.kim\/index.php?rest_route=\/wp\/v2\/posts\/1669","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.jungwon.kim\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.jungwon.kim\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.jungwon.kim\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.jungwon.kim\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1669"}],"version-history":[{"count":1,"href":"https:\/\/blog.jungwon.kim\/index.php?rest_route=\/wp\/v2\/posts\/1669\/revisions"}],"predecessor-version":[{"id":1670,"href":"https:\/\/blog.jungwon.kim\/index.php?rest_route=\/wp\/v2\/posts\/1669\/revisions\/1670"}],"wp:attachment":[{"href":"https:\/\/blog.jungwon.kim\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1669"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.jungwon.kim\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1669"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.jungwon.kim\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1669"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}