{"resolved":true,"match_type":"uuid","source_type":"original_book","book_id":"bbcce9bd-b637-4fa6-8a80-dadabab80104","title":"数字化生存 20周年纪念版","author":null,"edition":null,"publisher":null,"year":null,"isbn":"9787121307362","requested_by":"printed_page","book":{"source_type":"original_book","book_id":"bbcce9bd-b637-4fa6-8a80-dadabab80104","id":"bbcce9bd-b637-4fa6-8a80-dadabab80104","uuid":"bbcce9bd-b637-4fa6-8a80-dadabab80104","title":"数字化生存 20周年纪念版","normalized_title":"数字化生存20周年纪念版","author":null,"edition":null,"publisher":null,"year":null,"isbn":"9787121307362","isbns":["9787121307362"],"parsed":true,"ai_readable":true,"document_type":"book","page_count":362,"navigation_url":"https://workshop.closeclaw.top/ai/book/bbcce9bd-b637-4fa6-8a80-dadabab80104","title_url":"https://workshop.closeclaw.top/ai/title/%E6%95%B0%E5%AD%97%E5%8C%96%E7%94%9F%E5%AD%98%2020%E5%91%A8%E5%B9%B4%E7%BA%AA%E5%BF%B5%E7%89%88","fixed_page_url_template":"https://workshop.closeclaw.top/ai/book/bbcce9bd-b637-4fa6-8a80-dadabab80104/page/{printed_page}","path_api_url_template":"https://workshop.closeclaw.top/api/ai/book/bbcce9bd-b637-4fa6-8a80-dadabab80104/page/{printed_page}","read_url":"https://workshop.closeclaw.top/api/ai/read/bbcce9bd-b637-4fa6-8a80-dadabab80104","page_url":"https://workshop.closeclaw.top/api/ai/books/bbcce9bd-b637-4fa6-8a80-dadabab80104/page","search_url":"https://workshop.closeclaw.top/api/ai/books/bbcce9bd-b637-4fa6-8a80-dadabab80104/search"},"page":{"printed_page":14,"pdf_page":85,"physical_index":85,"physical_index_base":0,"printed_page_status":"recognized","page_sha256":"3c7f47852d3ab563ab434da62dff1ea96da889101187470b7b045f571474f732"},"chapter":"20周年纪念版 数字化生存 一本影响千百万人的互联网启蒙经典著作","content":"这些比喻忽略了不同的传输媒介（铜线、光纤、大气）之间一些微妙和重要的差别一一我们有能力根据我们设计（及调制）信号的方式，来决定在同样的铜线、光纤或大气中每秒传输多少比特。尽管如此，我们还是可以概略介绍一下电话铜线(telephonewire)、光纤（fiber）和无线电频谱（radio spectrum）的特点，让大家能够更好地了解没有重量的比特究竟是如何运动的。\n\n龟兔赛跑\n\n电话铜线通常被称为“双绞线”(twistedpair)，因为早期它们像辫子一样纠结在一起，恰如今天还能在一些古老而豪华的欧洲饭店中看到的电灯线一样。这种线路被看作带宽较窄的信道。尽管如此，美国有价值600亿美元的架设好的电话线，只要有合适的调制解调器，它们每秒能传输600万比特的信息。调制解调器能够把比特转换为波形，然后再把波形还原为比特。它通常的速率是9600比特/秒（bps)，或称9600波特（baud）(bps和baud在技术上的含义并不完全相同，但现在已可以互换使用，我在本书里也是这么用的。baud这个名称是为了纪念电信技术先驱Emile Baudot1]，就像电报中的“莫尔斯电码”以发明人莫\n\n014\n\nbeingdigital|数字化生存\n\n[1]埃米勒·波多（1845—1903)，法国发明家，发明电传打字机电码“波特码”(Baudotcode)。","previous_page":13,"next_page":15}