This document discusses basic concepts of memory. It describes the memory hierarchy from fastest to slowest as registers, cache memory, main memory, magnetic disks, and removable media. It also covers different types of read-only memory (ROM) like PROM, EPROM, and EEPROM. RAM types static RAM and dynamic RAM are compared in terms of cell design, density, cost, refresh requirements, and speed. Memory access time and cycle time are also defined.

1. Concepts of memory by D V Nagarjana Devi is licensed under a Creative Commons Attribution-ShareAlike 4.0
International License.

2. Basic Concepts of
Memory

3.  Stored Program concept-Von Neumann
 Memory is broadly classified into two categories
-Internal : Used by CPU to perform a task
-External : Used to store bulk information

4. Memory Hierarchy
 Register: reside in the CPU and stores the information brought from memory
into CPU
 Cache memory: Cache memory is a storage device placed in between CPU
and Main memory
 Main memory : provides storage and relatively slower memory than cache
memory.
 Magnetic disk: bulk storage device
 Removable media(Magnetic tape, CD,DVD etc): storing data which is not
currently used.

5. Types of ROM
 PROM– Programmable Read Only Memory: It can be programmed once as per
user requirements.
 EPROM-Erasable Programmable Read Only Memory: Contents of the memory
can be erased and store new data into memory.
 EEPROM-Electrically Erasable Programmable Read Only Memory: Contents of
particular location can be changed without effecting the contents of other
location.

6.  Memory Access Time: The time that elapses between the initiation of an
operation and the completion of the operation.
 Memory Cycle time: The minimum time delay between the initiation of two
independent memory operations.
 Memory cycle time is slightly larger than Memory Access time.

7. Tpyes of RAM
 Static RAM : Static Random Access Memory
Binary values are stored using traditional flip-flop constructed with
the help of transistors.
 Dynamic RAM: Dynamic Random Access Memory
DRAM is made up with cells that store data as charge on capacitors.

8. SRAM vs DRAM
 Both static and dynamic RAM’s are volatile , it will retain information as long as
power is supplied.
 A dynamic memory cell is simpler than static memory cell.
 DRAM is more dense i.e packing density is high.
 DRAM is less expensive than corresponding SRAM.
 DRAM requires the supporting refreshing circuitry.
 SRAM cells are faster than the DRAM cells.