{"id":3051,"date":"2020-04-04T22:04:15","date_gmt":"2020-04-04T14:04:15","guid":{"rendered":"https:\/\/www.aoisnow.net\/blog\/?p=3051"},"modified":"2020-04-04T22:04:15","modified_gmt":"2020-04-04T14:04:15","slug":"tont-37153-%e4%b8%ba%e4%bb%80%e4%b9%88-windows-95-%e7%9a%84%e5%ae%9a%e6%97%b6%e5%99%a8%e7%9a%84%e8%bf%90%e8%a1%8c%e9%a2%91%e7%8e%87%e6%98%af-55ms%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/www.aoisnow.net\/blog\/archives\/3051","title":{"rendered":"TONT 37153 \u4e3a\u4ec0\u4e48 Windows 95 \u7684\u5b9a\u65f6\u5668\u7684\u8fd0\u884c\u9891\u7387\u662f 55ms\uff1f"},"content":{"rendered":"

\u539f\u6587\u94fe\u63a5\uff1ahttps:\/\/devblogs.microsoft.com\/oldnewthing\/20041202-00\/?p=37153<\/a><\/p>\n

The story behind the 55ms timer tick rate goes all the way back to the original IBM PC BIOS. The original IBM PC used a 1.19MHz crystal, and 65536 cycles at 1.19MHz equals approximately 55ms. (More accurately, it was more like 1.19318MHz and 54.92ms.)<\/p>\n

\u5b9a\u65f6\u5668\u7684\u8fd0\u884c\u9891\u7387\u662f 55ms \u8ffd\u6839\u7a76\u5e95\u8981\u56de\u5230\u539f\u59cb\u7684 IBM PC BIOS \u4e0a\u3002\u6700\u521d\u7684 IBM PC \u4f7f\u7528\u4e86\u4e00\u9897 1.19MHz \u7684\u6676\u632f\uff0c\u800c 1.19MHz \u4e0a 65536 \u4e2a\u65f6\u949f\u5468\u671f\u6240\u9700\u7684\u65f6\u95f4\u5927\u7ea6\u5c31\u662f 55ms\u3002\uff08\u66f4\u51c6\u786e\u7684\u8bf4\uff0c\u5e94\u8be5\u662f 1.19318 MHz \u548c 54.92ms\u3002\uff09<\/p>\n

But that just pushes the question to another level. Why 1.19\u2026MHz, then?<\/p>\n

\u4e0d\u8fc7\u8fd9\u6837\u4e00\u89e3\u91ca\u53ea\u662f\u5c06\u95ee\u9898\u53c8\u63a8\u9ad8\u4e86\u4e00\u4e2a\u7ea7\u522b\uff0c\u4e3a\u4ec0\u4e48\u662f 1.19 MHz \u5462\uff1f<\/p>\n

With that clock rate, 216<\/sup> ticks equals approximately 3600 seconds, which is one hour. (If you do the math it\u2019s more like 3599.59 seconds.) [Update: 4pm, change 232 to 216; what was I thinking?]<\/p>\n

\u5728\u8fd9\u6837\u7684\u65f6\u949f\u9891\u7387\u4e0b\uff0c216<\/sup> \u4e2a\u5600\u55d2\uff08tick\uff09\u5927\u7ea6\u5c31\u662f 3600 \u79d2\uff0c\u4e5f\u5c31\u662f\u4e00\u5c0f\u65f6\u3002\uff08\u7cbe\u786e\u4e00\u4e9b\u7684\u8bdd\uff0c\u4e5f\u53ef\u4ee5\u8bf4\u662f3599.59 \u79d2\u3002\uff09<\/p>\n

What\u2019s so special about one hour?<\/p>\n

\u4e3a\u4ec0\u4e48\u300e\u4e00\u4e2a\u5c0f\u65f6\u300f\u8fd9\u4e2a\u5468\u671f\u90a3\u4e48\u7279\u522b\u5462\uff1f<\/p>\n

The BIOS checked once an hour to see whether the clock has crossed midnight. When it did, it needed to increment the date. Making the hourly check happen precisely when a 16-bit tick count overflowed saved a few valuable bytes in the BIOS.<\/p>\n

BIOS \u6bcf\u5c0f\u65f6\u4f1a\u68c0\u67e5\u4e00\u6b21\u7cfb\u7edf\u65f6\u949f\u6765\u786e\u5b9a\u662f\u5426\u8de8\u8d8a\u4e86\u5348\u591c\uff0c\u5f53\u8fd9\u79cd\u60c5\u51b5\u53d1\u751f\u65f6\uff0c\u7cfb\u7edf\u5c31\u4f1a\u5c06\u65e5\u671f\u5411\u524d\u63a8\u8fdb\u4e00\u5929\u3002\u8ba9\u8fd9\u79cd\u68c0\u67e5\u673a\u5236\u53d1\u751f\u572816\u4f4d\u5600\u55d2\u5b58\u50a8\u5668\u6ea2\u51fa\u7684\u65f6\u523b\uff0c\u53ef\u4ee5\u5728 BIOS \u4e2d\u8282\u7ea6\u5b9d\u8d35\u7684\u51e0\u4e2a\u5b57\u8282\u3002<\/p>\n

Another reason for the 1.19MHz clock speed was that it was exactly one quarter of the original CPU speed, namely 4.77MHz, which was in turn 4\/3 times the NTSC color burst frequency of 3.5MHz. Recall that back in these days, personal computers sent their video output to a television set. Monitors were for the rich kids. Using a timer related to the video output signal saved a few dollars on the motherboard.<\/p>\n

\u53e6\u4e00\u4e2a\u91c7\u7528 1.19MHz \u65f6\u949f\u9891\u7387\u7684\u539f\u56e0\u662f\u56e0\u4e3a\u8fd9\u4e2a\u503c\u6b63\u597d\u662f\u539f\u59cb\u8bbe\u8ba1\u4e2d CPU \u8fd0\u884c\u901f\u5ea6\u2014\u2014 4.77MHz \u2014\u2014\u7684\u56db\u5206\u4e4b\u4e00\uff0c\u800c\u8fd9\u6b63\u597d\u53c8\u662f NTSC \u5236\u5f0f\u7684\u5f69\u8272\u4fe1\u53f7\u9891\u7387\u7684\u4e09\u5206\u4e4b\u56db\u500d\uff08\u8bd1\u6ce8\uff1a\u6ca1\u6709\u6253\u9519\uff0c4.77\u9664\u4ee53.5\u7ea6\u7b49\u4e8e4\u9664\u4ee53\uff09\u3002\u5f53\u5e74\uff0c\u4e2a\u4eba\u7535\u8111\u662f\u5c06\u5176\u89c6\u9891\u4fe1\u53f7\u8f93\u51fa\u5230\u7535\u89c6\u4e0a\u7684\uff0c\u90a3\u65f6\u5019\u663e\u793a\u5668\u662f\u6709\u94b1\u4eba\u7684\u73a9\u5177\uff0c\u800c\u5c06\u5b9a\u65f6\u5668\u9891\u7387\u4e0e\u89c6\u9891\u4fe1\u53f7\u5173\u8054\u8d77\u6765\u5219\u53c8\u5728\u4e3b\u677f\u4e0a\u7701\u51fa\u4e86\u51e0\u7f8e\u5143\u7684\u6210\u672c\u3002<\/p>\n

Calvin Hsia has another view of the story behind the 4.77MHz clock.<\/a><\/p>\n

Calvin Hsia \u63d0\u4f9b\u4e86\u6709\u5173 4.77 MHz \u65f6\u949f\u9891\u7387\u7684\u53e6\u4e00\u4e2a\u89d2\u5ea6\u7684\u6545\u4e8b\u3002\uff08\u8bd1\u6ce8\uff1a\u94fe\u63a5\u5df2\u5931\u6548\uff09<\/p>\n

(Penny-pinching was very common at this time. The Apple ][ had its own share of penny-saving hijinks<\/a>.)<\/p>\n

\uff08\u90a3\u65f6\u5019\u4e00\u5206\u94b1\u63b0\u6210\u4e24\u534a\u82b1\u662f\u5f88\u5e38\u89c1\u7684\u4e8b\uff0cApple ][ \u6709\u5176\u81ea\u5df1\u7684\u7701\u94b1\u5c0f\u5999\u62db\u3002\uff09\uff08\u8bd1\u6ce8\uff1a\u94fe\u63a5\u5df2\u5931\u6548\uff09<\/p>\n","protected":false},"excerpt":{"rendered":"

\u539f\u6587\u94fe\u63a5\uff1ahttps:\/\/devblogs.microsoft.com\/oldnewthing\/2004120 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-3051","post","type-post","status-publish","format-standard","hentry","category-tont_history"],"_links":{"self":[{"href":"https:\/\/www.aoisnow.net\/blog\/wp-json\/wp\/v2\/posts\/3051","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.aoisnow.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.aoisnow.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.aoisnow.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.aoisnow.net\/blog\/wp-json\/wp\/v2\/comments?post=3051"}],"version-history":[{"count":0,"href":"https:\/\/www.aoisnow.net\/blog\/wp-json\/wp\/v2\/posts\/3051\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.aoisnow.net\/blog\/wp-json\/wp\/v2\/media?parent=3051"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.aoisnow.net\/blog\/wp-json\/wp\/v2\/categories?post=3051"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.aoisnow.net\/blog\/wp-json\/wp\/v2\/tags?post=3051"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}