2.4. Information Storage in μC

Now that we know how all the operations inside a μC or a μP are synced, let’s discuss where the information, on which these operations are applied, is stored. Specifically for a μC, the three places where information is generally stored are: Flash, RAM and Register.

2.4.1. Flash

Flash is an electrically programmable non-volatile memory. The term ‘Non-Volatile Memory’ means that it doesn’t require power to maintain the integrity of the information stored in it. It generally holds the program that would run on a μC. In current time, flash memory capacity for a μC varies from a couple of MBs to close to a GB since an external flash chip can be connected. Keep in mind that flash has the lowest data transfer rate out of all the places available on a μC for storing information. Moreover, the number of times a flash can be written with new information is limited. However, this limit is quite high so it’s not a major concern.

2.4.2. RAM

RAM, Random Access Memory, is a volatile memory, i.e. the information in the RAM is lost during power cycles. RAM generally contains the program or chunks of a program that might be running on the μC. The data transfer speed of a RAM is much higher than that of a flash. Moreover, a RAM can access and update any information stored in it anywhere while a flash has to do this process in big chunks. However, the capacity of RAM available in a μC is generally limited to a few MBs since the RAM has to be on the same chip as the μC.

2.4.3. Register

A register is the smallest element of information storage in a μC. A μC has the fastest access to the contents of a register. For the intents and purposes of this class, the registers can be split into two groups: Core registers and Configuration registers. The core registers are an essential part of the processor and hold the information or instructions that the μC is working on at that moment. The configuration registers on the other hand are part of the peripherals and are used to configure different aspects of a peripheral. Moreover, these configuration registers can have a predefined reset value so that a peripheral can be set to a known state when the μC starts up.

The size of all the registers inside a μC is fixed and can be 8-bits, 16-bits, 32-bits or 64-bits for different μCs. Note that these sizes are similar to the sizes of different data types available in programming. Thus, you can think of a register as a collection of blocks where each block contains a 0 or a 1. The information inside each block or bit may have a physical meaning in the case of a configuration register. Thus, a need may arise where you have to change a single bit of a 32-bit register.

Following two videos explain how exactly registers work if you want to know more.