Arch100X 01 Endianness

Summary

The video script delves into the concept of endianness, a term derived from Jonathan Swift's 'Gulliver's Travels', which humorously satirizes religious wars. It explains how data, such as the hexadecimal value 0x12345678, is stored in memory with either little-endian or big-endian format. Little-endian, used by Intel, stores the least significant byte at the lowest address, while big-endian does the opposite. The script clarifies that endianness applies to memory storage, not register representation, and discusses the impact on debugger display and network traffic, which typically uses big-endian order. It also touches on the evolution of RISC and ARM systems from being strictly big or little-endian to being configurable or 'bi-endian'.

Takeaways

• 📚 Endianness is a concept that can be confusing for those new to computer architecture, referring to the order in which bytes are stored in memory.
• 📖 The term 'endianness' originates from Jonathan Swift's 'Gulliver's Travels', satirizing the trivial disputes that can lead to conflict.
• 🔢 In 'little endian' systems, the least significant byte is stored at the lowest address, which can make values appear reversed when viewed in memory.
• 🔠 Intel processors are an example of little endian architecture, where memory values are stored with the least significant byte first.
• 🔀 'Big endian' is the opposite of little endian, storing the most significant byte at the lowest address, which is typical for network traffic.
• 🌐 Network protocols often use big endian byte order, which is why functions like 'htonl' and 'htons' are used to convert between host and network byte order.
• 🛠 Some RISC systems were initially big endian but later became configurable to be either big or little endian, known as bi-endian.
• 📱 ARM processors started as little endian and have since become bi-endian, allowing for configuration based on system requirements.
• 🚫 Endianness applies only to memory storage of values and not to the representation of values in registers, which are always shown in big endian form.
• 🛑 Endianness concerns the order of bytes, not individual bits within a byte, so bit flipping is not related to endianness.
• 🔑 Understanding endianness is crucial when working with memory at the byte level, especially when debugging or interfacing with different systems.

Q & A

What is the origin of the term 'endianness'?

The term 'endianness' originates from Jonathan Swift's 'Gulliver's Travels,' where it was used to satirize the religious wars between England and France over the correct way to eat soft-boiled eggs.

What does 'little endianness' mean in terms of memory storage?

In little endianness, the least significant byte of a value is stored at the lowest address, meaning the byte order is reversed when viewed in memory compared to its natural hexadecimal representation.

Which architecture is known for being little endian?

Intel architecture is known for being little endian.

What is the opposite of little endianness?

The opposite of little endianness is big endianness, where the most significant byte is stored at the lowest address.

How is network traffic typically sent?

Network traffic is typically sent in big endian order.

What does the term 'bi-endian' refer to?

Bi-endian refers to a system that can be configured to either be big endian or little endian, providing flexibility in byte order.

Which processor architecture initially started as big endian and later became configurable?

Many RISC systems initially started as big endian and later became configurable to be either big or little endian.

How does endianness relate to the representation of values in registers?

Endianness only applies to the memory storage of values and not to registers. Registers are always represented in big endian order, with the most significant byte on the left.

Does endianness affect the bit ordering within a byte?

No, endianness only affects the order of bytes in memory representation. The bits within a byte are always represented with the least significant bit on the right and the most significant bit on the left.

Can you provide an example of how memory representation differs between big and little endian architectures?

In a big endian architecture, the most significant byte (e.g., '12' in 0x12345678) would be stored at the lowest address, while in a little endian architecture, the least significant byte (e.g., '78' in 0x12345678) would be stored at the lowest address.

How does a debugger typically display memory values in relation to endianness?

Debuggers often display memory values in big endian form, meaning they will flip the byte order to match the big endian representation of registers when displaying multi-byte values.