Computerphile - Computer Timescales Mapped onto Human Timescales - Computerphile
The discussion begins with a comparison of human and computer speed in performing arithmetic operations. A human might take 10 seconds to add two four-digit numbers, while a computer can do it in half a nanosecond. This highlights the incredible speed of computers, which can perform multiple operations simultaneously due to their architecture. The video further explains how computers handle more complex operations like multiplication and division, which take more cycles but are still incredibly fast compared to human capabilities.
The video also delves into memory access, explaining the hierarchy of caches (L1, L2, L3) and RAM. Accessing data from RAM is significantly slower than from caches, akin to a human taking a trip to a corner shop versus finding something on their desk. The discussion extends to SSDs and network latency, illustrating the vast difference between computer processing speed and the time it takes to access data from storage or over a network. This comparison helps to appreciate the efficiency of modern computing systems in managing these delays.
Key Points:
- Computers can add numbers in half a nanosecond, showcasing their speed.
- Multiplication and division are more complex but still fast for computers.
- Memory access speed varies greatly, with RAM being the slowest.
- Caches (L1, L2, L3) help mitigate slow RAM access.
- Network latency and SSD access times highlight external speed limitations.
Details:
1. 🧠 Human vs Computer Speed: Basic Arithmetic
- Humans typically require 10-20 seconds to add two four-digit numbers using pen and paper, though this can vary based on individual skill and complexity of numbers.
- Using an estimated time of 10 seconds serves as a convenient reference for comparison.
- Computers perform the same arithmetic operations virtually instantaneously, highlighting the efficiency gap.
- Factors such as practice, familiarity with numbers, and cognitive load can affect human speed in arithmetic.
- Understanding human limitations in arithmetic can inform the design of tools and interfaces that aid calculation.
2. 🔢 Advanced Arithmetic Operations: Multiplication and Division
- A typical laptop can add two 32 or 64-bit numbers in a single clock cycle, translating to incredible speed at approximately 2 GHz (half a nanosecond per cycle).
- Human reaction times are significantly slower than a millisecond, highlighting the vast speed difference.
- The laptop can execute up to four additions simultaneously, illustrating its capability for parallel processing.
- Multiplication, more complex than addition, takes about four clock cycles to complete, demonstrating inherent computational challenges.
- For context, a task taking a human 10 seconds is completed by a computer in fractions of a second, with multiplication translating to roughly 20 seconds for a human, indicating computational efficiency even in complex operations.
3. 🧮 Floating Point Operations and Branch Prediction
3.1. Division Operations
3.2. Floating Point Operations
3.3. Algorithmic Implications
3.4. Floating Point Operations in Practice
4. 💾 Memory Access and Caching
4.1. Branch Prediction
4.2. Memory Access and Caching
5. 💿 From SSDs to Spinning Disks: Storage Speeds
- Reading an arbitrary block from a SATA SSD takes approximately 20 microseconds, highlighting the efficiency of SSDs over traditional spinning disks.
- In contrast, accessing a 512-byte block from a spinning disk can take as long as 2.3 days in computational terms, illustrating the significant speed disparity between SSDs and spinning disks.
- The latency difference between SSDs and spinning disks is so vast that the latter can be likened to storing data in a remote facility, a stark contrast to the near-instantaneous access provided by SSDs.
- Spinning disks operate with noticeable latency, often in the range of milliseconds, which can be perceptible to users, compared to the microsecond-level speeds of SSDs.
- Spinning disks typically rotate at 7200 RPM, indicating a mechanical nature that inherently limits speed compared to solid-state technology.
6. 🌐 Networking and Latency: Communication Delays
- Reading data from a spinning disc in older computing systems could take up to 3 years, highlighting significant delays compared to modern systems.
- Video games aim for 60 frames per second, allowing computers only 16 milliseconds per frame to process, which is equivalent to five years of compute time in a human-scaled comparison.
- Ping tests reveal a local router latency of 400 microseconds, whereas pinging Google can take about 10 milliseconds, equating to 16 weeks of compute time, demonstrating how internet distances increase delay.
- Pinging a web server in Nottingham shows latency equivalent to 31 years, emphasizing the vast differences in perceived vs. actual communication delays across different destinations.
- The examples showcase how perceived instantaneous digital communication can still involve substantial delays depending on technology and distance.
7. 🖥️ Multitasking and CPU Efficiency
- Computers perform multitasking by switching between tasks every 16 milliseconds, creating an illusion of simultaneous application execution, which is imperceptible to users.
- Techniques such as register renaming and out-of-order execution enhance CPU efficiency by allowing parallel processing of instructions before committing them in order.
- This technology significantly improves user experience by enabling seamless multitasking without visible delays, making computing efficient and user-friendly.