Assembly Language: Chapter 1 - Basic Hardware Knowledge

This series will explain the book “Assembly Language”. This section covers Chapter 1 – Basic Hardware Knowledge.

Overview of This Section
1. Machine Language and Assembly Language
2. Components of Assembly Language
3. Instructions and Data
4. Memory Units
5. CPU Read/Write Operations on Memory (Three Lines)
6. Transmission of Address, Data, and Control Information – Bus
7. Address Bus
8. Data Bus
9. Control Bus
10. Memory Address Space (Introduction)
11. Motherboard
12. Interface Cards
13. Various Types of Memory Chips
14. Memory Addressing Space (Detailed Explanation)

1. Machine Language and Assembly Language

Machine Language	Machine code that the CPU can execute directly
Assembly Language	Mnemonic form corresponding one-to-one with machine code mnemonic form
Compiler	Program that converts assembly language into machine code

The machine instructions of an electronic computer are a series of binary numbers. The computer converts them into a series of high and low levels to drive the computer’s electronic components to perform calculations.Note that different CPU architectures have different machine codes, and thus different assembly instruction sets.

Our programs can only execute in the CPU in the form of machine code, so assembly language needs to be converted into machine code, which requires the use of a compiler:

Assembly Language: Chapter 1 - Basic Hardware Knowledge

2. Components of Assembly Language

Category	Description	Corresponding Machine Code	Execution Entity
Assembly Instructions (Core)	Mnemonic for machine code	Yes	Computer (executes corresponding machine code)
Pseudoinstructions	No actual corresponding machine code logic, assists the compilation process	No	Compiler
Other Symbols (e.g., +, -, *, /, etc.)	Used to express operations and logic, participates in the compilation phase	No	Compiler

3. Instructions and Data

All our programs run in the CPU, and to make the CPU work, we must provide it with data and instructions. Data and instructions are stored in the memory, which we commonly refer to as RAM.

In disks and memory, data and instructions are indistinguishable, both are binary information, but when the CPU is working, it interprets them as data or instructions based on need.

This is like the pieces on a Go board; they are essentially the same in the box, but have different interpretations during a game.

For example, the binary information in memory 1000100111011000 can have the following interpretations:

Interpretation Type	Original Binary Information	Actual Interpretation
Data	1000100111011000	89D8H
Instruction	1000100111011000	mov ax,bx

4. Memory Units

The memory is divided into several memory units, each unit is sequentially numbered starting from 0. For example, if a memory has 128 units, the numbering goes from 0 to 127. These numbers can be seen as the addresses of the memory units in the memory. Just like a street, each house has a house number. As shown in the figure:

5. CPU Read/Write Operations on Memory (Three Lines)

To read data from memory, the CPU must first specify the address of the memory unit (i.e., the aforementioned unit number). In other words, it must first determine which memory unit’s data it wants to read. This is like finding someone on a street; you must first determine which house they live in.

Thus, for the CPU to perform data read/write operations with the outside world, it needs the following three types of information:

Required Information	Explanation
Address Information	Address of the memory unit (address information)
Data Information	Data to be read or written (data information)
Control Information	Device selection, read or write command (control information)

6. Transmission of Address, Data, and Control Information – Bus

From the above, we know that the CPU needs to obtain three types of information to perform data read/write operations with the outside world. So how is this information transmitted to the memory chip?

Clearly, electronic computers use electrical signals, so they use wires for transmission. In computers, there are wires specifically connecting the CPU and other chips, known as “bus”.

Visualizing the Bus:

Bus Perspective	Explanation
Physically	A collection of wires
Logically	Address Bus, Control Bus, Data Bus

Functions of Each Bus:

Bus	Function
Address Bus	The width of the address bus determines the CPU’s theoretical addressing capability
Data Bus	The width of the data bus determines the amount of data transferred at once between the CPU and other devices
Control Bus	The width of the control bus determines the CPU’s control capability over other devices in the system

Practical Demonstration as Shown:

Corresponding Process:

(1) The CPU sends out address information 3 through the address line.

(2) The CPU sends out a memory read command through the control line, selects the memory chip, and notifies it to read data from it.

(3) The memory sends the data 8 from unit 3 through the data line to the CPU.

7. Address Bus

Address Bus Related
Purpose	The CPU selects the specified memory unit through the address bus.
Addressing Range	The number of memory units the CPU can select through the address bus is the size of the addressing range.

For example, if the size of an address bus is N, then the addressing range is clearly 0~2^N-1, because each line has 2 variations.

For instance, a CPU with 10 address lines can address memory address 11 as shown in the following diagram:

8. Data Bus

After the CPU selects the address through the address bus, it begins the data transfer. The data transfer between the CPU and memory or other devices is done through the data bus. The width of the data bus determines the data transfer rate between the CPU and the outside world. For example, 8 data lines can transfer 8 bits of binary information (i.e., 1 byte) at once.

Assuming the data to be transferred is 89D8H, the following shows the data transfer situation under 8-bit and 16-bit data buses:

Assembly Language: Chapter 1 – Basic Hardware Knowledge