Introduction
Most students are involved in software development, but how much do you know about Android device hardware?
1. Screen
There are many terms you need to understand about screens, such as LCD and OLED, high refresh rates, and the popular LTPO technology from last year.
Before discussing the professional terms related to screens, let’s start with some basic knowledge.
1. Resolution
As we all know, the content displayed on the screen is made up of tiny pixels, which are so small that they are indistinguishable to the naked eye.
For example:
For instance, my phone has a resolution of 2376 * 1080, which means the longer side can hold 2376 pixels, and the shorter side can hold 1080 pixels.
When people buy phones, they often mention 2K screens, which are generally classified as follows:
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720P: 1280 * 720 -
1K screen: 1920 * 1080 -
2K screen: 2560 * 1440
When Lei Jun promotes mobile phone screens, he often mentions a term called PPI. What is that?
PPI stands for pixels per inch, calculated as follows:
Taking my phone as an example, the resolution is 2376 * 1080, and the screen size is 6.57 inches.
The calculation formula is: the square root of (2376^2 + 1080^2), divided by 6.57, which results in 397.
Many Android developers often find resolution headaches due to the serious fragmentation problem in Android, with too many resolutions to adapt to.
2. LCD and OLED
In recent years, high-end models have adopted OLED screens. Does that mean OLED screens are better?
2.1 Display Principle
To understand the differences between these two types of screens, we first need to know about the three primary colors of light: red, green, and blue. By configuring different proportions, we can create different colors.
Each pixel on the screen is made up of three sub-pixels, like this:
Although both methods are used, the principles of LCD and OLED are quite different. Simply put, LCD uses a backlight, while OLED is self-luminous.
Here are their design diagrams:
LCD emits uniform white light from the back, which passes through red, green, and blue color films to create the three primary colors. If we do not process it, the combination of red, green, and blue still results in white light. Therefore, an intermediate layer is added as a switch, which is the so-called liquid crystal part that can change the degree of opening and closing, altering the intensity of light emitted, thus allowing the three colors to form different light.
The principle of OLED is simpler; it is like a small lamp that can control the intensity of red, green, and blue light.
Thus, for LCD, even if the screen is completely black, the backlight still needs to emit light, which is often referred to as light leakage.
Let’s also discuss the differences in pixel arrangement:
LCD generally uses RGB arrangement (left image), while OLED typically uses Pentile arrangement (right image). This leads to the issue where, under the same size, OLED screens have fewer pixels, hence the saying:
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No 2K (2560X1440), no A screen (AMOLED screen)
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2.2 Advantages and Disadvantages
Compared to LCD, OLED has:
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Advantages: Thinner, can be used as flexible screens, more vibrant colors, can light up individually saving energy, fast screen response -
Disadvantages: Prone to burn-in, flickering, pixel density
For a more detailed understanding of the differences between them, you can refer to:
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“What is the difference between OLED and LCD?”
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3. Screen Refresh Rate
It seems that starting from the year before last, major manufacturers have launched 120 HZ high refresh rate phones.
120 HZ means that the screen can draw 120 frames per second. If we describe it visually, it looks like this:
I remember when a colleague first got a high refresh rate phone, they said, “Once you use a high refresh rate phone, you can’t go back!”
However, a higher refresh rate means higher energy consumption.
Starting from 2021, major manufacturers have introduced LTPO technology.
“LTPO” stands for “Low Temperature Polycrystalline Oxide”, which means low-temperature polycrystalline oxide.
In simple terms, it can dynamically change the refresh rate of the screen.
For example, when we are reading a novel, we do not need a 120 HZ refresh rate, so the phone will set the frame rate to 30 HZ, while when playing games, we need a high refresh rate, and the phone will switch the frame rate back to 120 HZ. Of course, this requires the game to support high refresh rates, allowing for lower energy consumption and extended battery life.
For more detailed knowledge, you can refer to:
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“LTPO Technology Popularization: The Next Industry Benchmark for Mobile Screens”
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2. RAM
RAM refers to the running memory. In recent years, Android phones typically start with 8GB of RAM, with some high-end models reaching 16 GB.
Regarding RAM, the most common term heard is LPDDR. Lei Jun has put a lot of effort into promoting LPDDR5:
Take a look at the family tree of LPDDR:
DRAM is a way to store data in memory. It works by charging capacitors, calculating the difference in capacitance, and converting it into binary. However, capacitors can leak, so they need to be periodically charged. Therefore, the D in DRAM stands for dynamic.
The CPU frequency is generally measured in GHZ, for example, the latest Snapdragon 8 Gen1 has a maximum single-core frequency of 3.0 GHZ.
The working frequency of RAM is still measured in MHZ, so the CPU and RAM must reach an agreement that the CPU will always be able to access data within a specified cycle without waiting. Thus, the S in SDRAM stands for synchronous.
DDR should actually be called DDR SDRAM, with the SDRAM part omitted. DDR stands for Double Data Rate, meaning double speed:
In the past, data storage was done once per clock cycle, but now it can be done twice, once on the rising edge and once on the falling edge, significantly improving efficiency.
Finally, we introduce LPDDR, where LP stands for Low Power. Its full name is Low Power Double Data Rate SDRAM, a standard established by the American JEDEC Solid State Technology Association for low-power memory.
LPDDR has low power consumption, small size, and is inherently suitable for mobile devices. Let’s take a look at the parameters of LPDDR:
In November 2021, Samsung developed the latest LPDDR5X DRAM, which improved speed by 30% and reduced power consumption by 20%.
3. ROM
“ROM is called read-only memory, unlike RAM, it does not lose data when the power is turned off.” Moreover, it refers to the numbers like 32G, 64G, 128G, etc., that are marked when purchasing the phone, which determines how much video and games our phone can store.
Remember the joke from back then, “Lu Xun said, don’t buy a phone with 16G of storage!”
1. Classification of ROM
Although ROM is read-only memory and cannot be written to, similar to the area in Android devices where the system storage cannot be modified or deleted, for user convenience, the following types have emerged:
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Programmable Read-Only Memory (PROM) -
Electrically Erasable Programmable Read-Only Memory (EEPROM) -
Flash Memory (e.g., EEPROM)
The ROM used in mobile devices is flash memory, defined as:
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Flash memory is a type of electronic erasable programmable read-only memory that allows multiple erase or write operations during operation.
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Flash memory is a special type of EEPROM that is erased in macro blocks. It is low cost, data is not easily lost, and has high reliability, making it widely adopted in mobile devices.
2. UFS and eMMC
When manufacturers promote their phones, they often mention UFS 3.1. What is that?
The common classifications of flash memory are SSD, eMMC, and UFS.
SSD is used in PCs; I remember back in college when I replaced the mechanical hard drive in my laptop with an SSD, and it felt like a new machine, allowing me to play games much better.
“eMMC and UFS are designed for mobile devices, characterized by small size, low power consumption, and moderate performance. In recent years, many manufacturers have launched 1TB large-capacity phones, aiming to surpass PCs.”
In recent years, most phones have adopted UFS, abandoning eMMC because UFS uses a serialized interface to increase transmission frequency. Here are the parameters of UFS:
eMMC, on the other hand, has a bandwidth of only 400 MB/S, so abandoning eMMC is inevitable.
For more detailed information, refer to:
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“How UFS 3.1 Makes App Launch and Load Speeds Faster?” “A Brief Discussion on SSD, eMMC, UFS”
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3. File System
When we learn about IO invocation chains in Android:
We often see the term file system. VFS provides a unified file interface for applications, while the specific implementation is handled by the file system.
Currently, mainstream file systems include ext4 and F2FS. For example, my Android phone:
My Vivo X70 Pro uses F2FS for internal storage and ext4 for system storage.
“For apps, random I/O scenarios are more frequent, so internal storage at the application level is more suitable. However, under the same conditions, F2FS occupies more storage space, about 1.1 to 1.5 times that of ext4, and its performance in reading and writing large files continuously is not as strong as ext4, so the system storage chooses ext4.”
4. Processor
The processor is the brain of the phone. Common processors in Android phones include Qualcomm Snapdragon series, MediaTek Dimensity series, Huawei Kirin series, and Samsung Exynos series, with the Snapdragon series holding the highest market share.
Typically, in PCs, the processor refers to the CPU, such as Intel Core i7-12700.
The processors in mobile devices are different. Considering size and power consumption, they use highly integrated SoCs (System on Chip), with a processor concentrating key parts of the system into one chip.
1. What Does SoC Integrate?
Though small, SoC contains everything:
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Central Processing Unit (CPU) -
Graphics Processing Unit (GPU) -
Image Signal Processor (ISP) -
Digital Signal Processor (DSP) -
Neural Processing Unit (NPU) -
Modem -
And other functional modules
Here’s the layout of the latest Snapdragon 8 Gen SoC:
Many important components have been labeled.
Through SoC integration, it maximizes motherboard layout efficiency, helps slim down devices, enhances communication speed between IP units, and significantly reduces overall power consumption.
2. Process Technology
The SoC in mobile devices is cut from a whole silicon wafer. The more advanced its process technology, the higher the maximum frequency can be unlocked, with lower heat generation, lower power consumption, and more stable performance!
Therefore, manufacturers will always mention the xxnm process when introducing chips.
For example, the latest Snapdragon 8 Gen1 uses Samsung’s 4nm process, while MediaTek’s Dimensity 9000 uses TSMC’s 4nm process. Although both are 4nm, TSMC’s 4nm process is slightly stronger.
3. CPU
The CPU is one of the most critical core units in SoC, determining the phone’s performance.
Taking the latest Snapdragon processor as an example, it is an octa-core processor:
It includes:
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1 * 3.0GHz Cortex-X2 big core -
3 * 2.5GHz Cortex-A710 middle cores -
4 * 1.8GHz Cortex-A510 small cores
It has been proven that when SoC runs at full speed (e.g., gaming), it tends to heat up and throttle, which is why the big, medium, and small core design is trending today.
Apart from the CPU layout, we also need to understand basic architecture knowledge.
When writing Android programs, we often need to be compatible with different CPU architectures, such as common arm architectures (ARM v5), armeabi-v7a (ARM v7), arm64-v8a (ARM v8), and x86.
In simple terms:
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ARM architecture processors originate from RISC (Reduced Instruction Set Computing), optimizing common commands to provide a simpler and more efficient execution environment. RISC leaves complexity to the compiler, sacrificing program size and instruction bandwidth for simpler and lower-power hardware implementation. -
x86 architecture corresponds to CISC (Complex Instruction Set Computing), increasing the complexity of the processor itself at the cost of higher performance.
Thus, the low-power and high-efficiency ARM architecture is clearly more suitable for mobile devices. It’s worth mentioning that last year, Apple’s latest MacBook Pro adopted the M1 chip, which is also based on the ARM architecture.
4. GPU
The GPU corresponds to the graphics card in mobile devices. The maximum resolution, refresh rate, and frame rate a phone can support for gaming largely depend on the GPU. It provides many graphics rendering interfaces for games and applications, such as the common OpenGL.
Common GPUs include Qualcomm’s Adreno series and Arm’s Mali series.
For more knowledge about processors, you can read:
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“Snapdragon 8 Gen1 Parameters Revealed: Qualcomm’s First 4nm Chip, Comprehensive Performance Upgrade” “Why is Snapdragon 865 the Best? Understanding CPU and GPU Architecture” “Hardcore Science! Why the Performance of SoC Depends on Architecture and Process?”
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Conclusion
Even for application-level development engineers, it is inevitable to encounter hardware-related knowledge when reading relevant documents. Therefore, learning some basic hardware knowledge is somewhat necessary.
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