Misc/abrash-black-book
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Retidy, removing align=left from headings and empty paragraphs

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James Gregory 2013-12-30 15:37:13 +11:00
commit a96a114403
362 changed files with 8472 additions and 5040 deletions
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@ -1,5 +1,4 @@
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
@ -19,17 +18,21 @@
<center>
<table border="1">
<tr>
<td><a href="04-02.html">Previous</a></td>
<td>
<a href="04-02.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
<td>
<a href="index.html">Table of Contents</a>
</td>
<td><a href="04-04.html">Next</a></td>
<td>
<a href="04-04.html">Next</a>
</td>
</tr>
</table>
</center>
<p><br /></p>
<p>Back to the 8-bit bus cycle-eater. As I&rsquo;ve said, in 8088 work you should strive to use byte-sized memory variables whenever possible. That does <i>not</i> mean that you should use 2 byte-sized memory accesses to manipulate a word-sized memory variable in preference to 1 word-sized memory access, as, for instance,</p>
<pre>
mov dl,byte ptr [MemVar]
@ -105,16 +108,20 @@ shr ax,1
<p>should execute in 10 cycles, since each <b>SHR</b> takes 2 cycles to execute, according to Intel&rsquo;s specifications. Those specifications contain Intel&rsquo;s official instruction execution times, but in this case&mdash;and in many others&mdash;the specifications are drastically wrong. Why? Because they describe execution time <i>once an instruction reaches the prefetch queue.</i> They say nothing about whether a given instruction will be in the prefetch queue when it&rsquo;s time for that instruction to run, or how long it will take that instruction to reach the prefetch queue if it&rsquo;s not there already. Thanks to the low performance of the 8088&rsquo;s external data bus, that&rsquo;s a glaring omission&mdash;but, alas, an unavoidable one. Let&rsquo;s look at why the official execution times are wrong, and why that can&rsquo;t be helped.</p>
<p><br /></p>
<center>
<table border="1">
<tr>
<td><a href="04-02.html">Previous</a></td>
<td>
<a href="04-02.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
<td>
<a href="index.html">Table of Contents</a>
</td>
<td><a href="04-04.html">Next</a></td>
<td>
<a href="04-04.html">Next</a>
</td>
</tr>
</table>
</center>