CPU speed or clock speed is one factor that determines computer performance. The higher the CPU speed, the faster the computer can perform calculations and run programs. In the 1970s to 2000s, CPU speeds increased drastically from a few megahertz (MHz) to several gigahertz (GHz).
However, in the last decade, the increase in CPU speed seems to slow down and stagnate between 3-5 GHz. Why is this happening? What hinders the development of CPU speed? Is there a maximum limit for CPU speed?
Bardimin will answer these questions by explaining some factors that affect CPU speed and the challenges faced by engineers and scientists in improving CPU speed.
Factors Affecting CPU Speed
CPU speed can be measured in two ways, namely clock rate and instructions per cycle (IPC). The clock rate is the number of cycles a CPU can perform in one second. The unit used to measure clock rate is the hertz (Hz), which means one cycle per second. Instructions per cycle (IPC) are the number of instructions that the CPU can execute in a cycle.
Instructions are basic commands that can be understood by the CPU, such as addition, subtraction, multiplication, division, and so on. The number of instructions that the CPU can execute in a single cycle depends on the design and architecture of the CPU. CPU speed can be calculated by multiplying the clock rate and IPC. For example, if the CPU has a clock rate of 4 GHz and IPC 2, then the CPU speed is 8 billion instructions per second.
Factors that affect clock rate and IPC include:
1. Transistor size
A transistor is an electronic component that functions as a switch to control the flow of electric current. Transistors can change form on (conducting current) to off (stopping current), or vice versa, quickly. Transistors are used to form logic gates, which are circuits that can perform logical operations, such as AND, OR, NOT, and so on.
Logic gates are used to form circuits, which are circuits that can perform certain functions, such as addition, subtraction, multiplier, and so on. Circuits are used to form units, parts of the CPU that perform certain tasks, such as arithmetic, logic, control, memory, and so on. The units are used to form the CPU. So, transistors are the basic elements of the CPU.
The smaller the transistor size, the more transistors can fit into the CPU. The more transistors loaded into a CPU, the more logic gates, circuits, and units can be created in the CPU. The more logic gates, circuits, and units created in the CPU, the higher the IPC the CPU can reach.
In addition, the smaller the transistor size, the shorter the distance that the electric current in the CPU must travel. The shorter the distance that the electric current in the CPU must travel, the faster the CPU can change from one state to another. The faster the CPU can change from one state to another, the higher the clock rate the CPU can achieve. So, transistor size positively affects CPU speed.
2. Voltage and power
Voltage is the difference in electric potential between two points. Power is the rate of electrical energy consumed or emitted by a device. Voltage and power are closely related to CPU speed. The higher the voltage applied to the CPU, the stronger the electric current flowing in the CPU.
The stronger the electric current flowing in the CPU, the faster the CPU can change from one state to another. The faster the CPU can change from one state to another, the higher the clock rate the CPU can achieve. So, voltage positively affects CPU speed.
However, voltage also negatively affects CPU speed. The higher the voltage applied to the CPU, the greater the power consumed by the CPU. The greater the power consumed by the CPU, the greater the heat generated by the CPU.
The greater the heat generated by the CPU, the higher the temperature that the CPU must handle. The higher the temperature that the CPU has to handle, the greater the risk of damage or failure that can occur to the CPU. So, voltage negatively affects CPU speed.