Difference 'instruction RAM' and 'variables RAM' ?

[arjen1]

Dear forum

Till now I never worried too much about RAM size in my projects, but today I noticed this after compiling a rather large program:

Code: Select all

. Variables and constants in RAM (global, static), used 48480 / 80192 bytes (60%)
║   SEGMENT  BYTES    DESCRIPTION
╠══ DATA     1724     initialized variables
╠══ RODATA   13932    constants       
╚══ BSS      32824    zeroed variables
. Instruction RAM (IRAM_ATTR, ICACHE_RAM_ATTR), used 61499 / 65536 bytes (93%)
║   SEGMENT  BYTES    DESCRIPTION
╠══ ICACHE   32768    reserved space for flash instruction cache
╚══ IRAM     28731    code in IRAM    
. Code in flash (default, ICACHE_FLASH_ATTR), used 409604 / 1048576 bytes (39%)
║   SEGMENT  BYTES    DESCRIPTION
╚══ IROM     409604   code in flash  

Instruction RAM is 93% occupied.

I tried to put some Serial.print statements in Flash with the 'F' macro. The 1st number -Variables and constants in RAM- lowered, but nothing happens to the Instruction RAM number.

So the questions are:
1 What is Instruction RAM?
2 what is the difference between the 2 RAM?
3 Should I worry that it is 93% upon compilation?
4 What to do to lower this number?

Thanks.

It is an ESP8266 NodeMCU ESP12F
Using arduino IDE 2.3.4