Memory System Architecture

For this chapter, i'll explain the purpose and function of Memory System Architecture.

Early computers use the likes of vacuum tubes, switching elements, mercury delay lines and etc. They are very expensive and unreliable.

Then, magnetic cores were introduced in the 1960's. The core represents 1-bit of information. It can be magnetized in two ways ( clockwise and anticlockwise ). Still, it was very expensive and slow.

Since then, all computers have used solid state drives, which is essentially integrated circuits.

Memory capacity are measured in bytes.

Characteristics of Computer Memory System

     Location

           -  Located mainly in three places:

             

                                                            1) CPU

                                                            2) Internal

                                                            3) External

         - Processors require its own local memory in the form of registers.

         - Cache is another form of memory.

         - Internal memory is usually referred to as the main memory.

       - External memory consists of peripheral storage devices that are accessible to the processor via I/O          devices

Capacity

         - The total number of bits that can be stored.

         - Internal memory capacity is typically referred  to as bytes or words. Common word lengths are 8, 16 and 32 bits.

         - External memory capacity are expressed as bytes.

Unit of Transfer

            - For internal memory, unit transfer is equal to the number of lines into and out of the memory module.

            - Internal

                 Governed by data bus width

           - External

                 A block much larger than a word

           - Addressable Unit

                Smallest uniquely addressed location. The relationship between lengths in bits A of an address and number N of addressable units is —2A  = N

Access Methods

          - Sequential

          - Direct

          - Random

          - Associative

Performance

          - Access time

          - Transfer rate

          - Memory cycle time

Physical Types

         - Volatile memory
         - Non-volatile memory
         - Magnetic surface memory
         - Semi-conductor memory
         - Non-erasable memory

Physical Characteristics

         - Volatility
         - Erasable
         - Power consumption

Organization

         - Physical arrangements of bits into words.
         - e.g Interleaved.

Memory Hierachy

         

 

Locality of Reference

Semiconductor MemoryTypes

RAM (Random Access Memory)

                - Read/Write

                - Volatile

                - Static or Dynamic

Memory Cell Operation

Dynamic RAM

                     - Bits stored as charge in capacitators

                     - Charges leak

                     - Simpler construction

                     - Less expensive

DRAM Operation

                  - Address line active when bit is written or read
                  

SRAM vs DRAM

 ROM

Types of ROM

Cache

Mapping Function

Associative Mapping

Set Associative Mapping

Cache Replacement

CMOS

Types of External Memory

RAID