---
title: Declarations
TARGET DECK: Obsidian::STEM
FILE TAGS: x86-64
tags:
  - x86-64
---

## Overview

| C Declaration | Intel Data Type  | Suffix | Size (bytes) |
| ------------- | ---------------- | ------ | ------------ |
| `char`        | Byte             | `b`    | 1            |
| `short`       | Word             | `w`    | 2            |
| `int`         | Double word      | `l`    | 4            |
| `long`        | Quad word        | `q`    | 8            |
| `char *`      | Quad word        | `q`    | 8            |
| `float`       | Single-precision | `s`    | 4            |
| `double`      | Double-precision | `l`    | 8            |

%%ANKI
Basic
What is the width of a `word`?
Back: 16 bits.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523806-->
END%%

%%ANKI
Basic
What historical reason explains why a `word` is 16 bits?
Back: Because the 8086 that introduced x86 was 16 bits.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523813-->
END%%

%%ANKI
Basic
What is the width of an Intel `byte`?
Back: $8$ bits
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523816-->
END%%

%%ANKI
Basic
Which Intel data types are 1 bytes wide?
Back: Just the `byte`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523818-->
END%%

%%ANKI
Cloze
The {`byte`} Intel data type has assembly-code suffix {`b`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523821-->
END%%

%%ANKI
Basic
What is the width of an Intel  `word`?
Back: $16$ bits
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523824-->
END%%

%%ANKI
Basic
Which Intel data types are 2 bytes wide?
Back: Just the `word`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523827-->
END%%

%%ANKI
Cloze
The {`word`} Intel data type has assembly-code suffix {`w`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523830-->
END%%

%%ANKI
Basic
What is the width of an Intel `double word`?
Back: $32$ bits
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523833-->
END%%

%%ANKI
Basic
Which Intel data types are 4 bytes wide?
Back: The `double word` and `single-precision`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523836-->
END%%

%%ANKI
Cloze
The {`double word`/`double-precision`} Intel data type has assembly-code suffix {`l`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523839-->
END%%

%%ANKI
Basic
*Why* do `double word`s have assembly-code suffix `l`?
Back: The suffix stands for "long", relative to a 16-bit `word`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523842-->
END%%

%%ANKI
Basic
What is the width of an Intel  `quad word`?
Back: $64$ bits
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523846-->
END%%

%%ANKI
Basic
Which Intel data types are 8 bytes wide?
Back: The `quad word` and `double-precision`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523850-->
END%%

%%ANKI
Cloze
The {`quad word`} Intel data type has assembly-code suffix {`q`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523853-->
END%%

%%ANKI
Cloze
C integral declaration {`char`} corresponds to Intel data type {`byte`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
<!--ID: 1711116523858-->
END%%

%%ANKI
Cloze
C integral declaration {`short`} corresponds to Intel data type {`word`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
<!--ID: 1711116523862-->
END%%

%%ANKI
Cloze
C integral declaration {`int`} corresponds to Intel data type {`double word`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
<!--ID: 1711116523866-->
END%%

%%ANKI
Cloze
C integral declaration {`long`} corresponds to Intel data type {`quad word`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
<!--ID: 1711116523870-->
END%%

%%ANKI
Cloze
C declaration `char *` corresponds to Intel data type {`quad word`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
<!--ID: 1711116523874-->
END%%

%%ANKI
Cloze
C floating-point declaration {`float`} corresponds to Intel data type {`single-precision`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
<!--ID: 1711116523877-->
END%%

%%ANKI
Cloze
The {`single-precision`} Intel data type has assembly-code suffix {`s`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523881-->
END%%

%%ANKI
Cloze
C floating-point declaration {`double`} corresponds to Intel data type {`double-precision`}.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: c17
<!--ID: 1711116523885-->
END%%

%%ANKI
Basic
What is the width of an Intel `single-precision`?
Back: $32$ bits
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523889-->
END%%

%%ANKI
Basic
What two Intel data types do floating-point numbers come in?
Back: `single-precision` and `double-precision`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523893-->
END%%

%%ANKI
Basic
Assembly-code suffix `l` is used for what two Intel data types?
Back: `double word`s and `double-precision`s.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523898-->
END%%

%%ANKI
Basic
What is the width of an Intel  `double-precision`?
Back: $64$ bits
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523903-->
END%%

%%ANKI
Basic
Why is it safe for `double word`s and `double-precision`s to both use assembly-code suffix `l`?
Back: Floating-point code uses a different set of instructions and registers.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1711116523908-->
END%%

## Bibliography

* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.