CPU memory-
DRAM-dynamic RAM- 
1.it is using capacitors to store data and these capacitors are constantly and 
2. dynamically refreshed often with electicity in order to store data.

SRAM(static ram)-another type of memory that computer uses that 
1.doesn't have to be refreshed and it is used as CPU cache. 
2.It is faster than dram because it doesn't contantanly refreshed.
3. expensive

CPU cache - it is CPU internal memory.
1. it stores copies of data and instructions from RAM, that is waiting to be used by the CPU.
2. it holds the data which CPU used over and over again becoz when CPU needs access of certain data it always checks the faster cache memory first ,if data in need is there , if it's not then CPU go back to the slower primary memory or RAM to get the data it needs.

3.so that is why cache memory is so important..so main idea of cache is to make the computer run faster at cheaper price..
4. computer can run without CPU cache but it would so slower even though the RAM becoming faster it still can't feed data to the CPU fast enough becoz CPU is so fast that lot of time CPU is waiting to get data and do nothing which creates bottleneck...so CPU cache reduces bottleneck..

CPU Cache comes in 3 different levels-
1. level 1 cache- it is also called primary cache. it is located on the processor.Runs at the same speed as the processor. fastest cache on the computer.
2. Level 2 cache-used to catch recent data accesses from the processor that were not caught by the level 1 cache. in the earlier computers, level  cache was located on a separate chip on the motherboard. In modern CPUs level 2 cache is located on the processor. level 2 cache is larger than level 1 cache but it is not as fast as level 1 cache.
3. level 3 cache- used ot catch recent data accesses fromt eh processor that were not caught by the level 2 cache.level 3 cache is located on the processor. level 3 cache is larger than level 2 cache but it's not fast as level 2 cache. 
level 3 cache is often referred as shared cache as it is memory is shared between all the cores in the CPU whereas level 1 and level 2 cache are dedicated to their own CPU core.