Working of computer Instructions
In order to understand what actually is MT/s and MHz, you need to understand how the computer performs its instructions. The computer actually works on clock cycles. It performs its instruction when there is a positive/negative edge or level of clock depending on the architecture of the computer. Some architectures perform instructions on both the positive and negative edge of clock cycles which means they can perform 2 instructions per clock cycle.
For example, if the computer requires to add to variables A and B, it can only perform this instruction when the edge or level of the clock has arrived.
The picture above shows the representation of the clock cycle. Let say your computer has a positive edge-triggered architecture, then it would perform each instruction at the positive edge of this clock cycle shown above.
Meaning of MT/s and MHz
MT/s stands for mega transfer per second, it means how much instructions it can perform in 1 second. 1MT/s means your ram can perform 1 Million instructions per second, 2 MT/s means your ram can perform 2 Million instructions per second, and so on. In simple words, it is a measure of the number of instructions that can be performed in one second.
MHz means how many clock cycles occur in one second. 1MHz means 1 million clock cycles will occur in 1 second, 2MHz means 2 Million clock cycles will occur in 1 second. In simple words, it is a measure of the number of clock cycles that occur in one second. If your ram performs 1 instruction per clock cycle then 1MHz means it can perform 1 Million instructions per second and 2MHz means 2 Million instructions in 1 second.
Difference between MT/s and MHz
From the above discussion, it might seem MT/s and MHz are the same but hang there it is not true. It might be true in the past but with the invention of new DDR rams, it is not true anymore. The actual difference between them can be demonstrated through the example of DDR ram.
DDR stands for double data rate which means it can perform 2x instructions at 1 clock cycle (one at the positive edge and one at the negative edge of a clock cycle). Now, as mentioned above MT/s is the measure of the number of instructions per second while Mhz is the measure of the number of clock cycles per second and DDR ram can perform 2x instructions per clock cycles its effective instruction performing capability becomes double. If your ram has MT/s of 1333 it means it can perform 1333 instructions per second. But if you have DDR ram and it has a clock speed of 1333MHz it means it can perform 2666 instructions per second because there are 1333 clock cycles and at each clock cycle it performs 2 instructions. So 2 x 1333 = 2666 simple mathematics!
Some people think that MHz and MT/s are the same, but it is not actually true. MT/s is a measure of the number of instructions your ram can perform in 1 second while MHz is the measure of clock cycles in 1 second and rams nowadays perform more than 1 instruction per clock cycle.