Chapter 4: Memory System Architecture

1.) 8 Characteristic of Computer Memory Systems

2.) Memory Hierarchy

3.) Semiconductor Memory Types

a.) Read/ Write memory

        i.) DRAM (Dynamic Random Access Memory)

            - bits stored as charge in capacitors.

            - charges leak.

            - need refreshing even when powered.

       ii.) SRAM (Static Random Access Memory)

             - bit stored as on/off switches.

             - no charges to leak.

             - no refreshing needed when powered.

b.) Read Only memory (ROM)

        i.) PROM (Programmable Read-Only Memory)

           - can be programmed only ONCE.

           - nonvolatile, writing process performed electrically at a time
             later.

        ii.) EPROM (Erasable Programmable Read-Only Memory)

            - erased by UV and can be altered many times.

            - before write, all must be erased.

        iii.) EEROM (Electrically Erasable Read-Only Memory)

           - write at anytime without erasing prior contents electrically.

           -  location can be selectively erased and programmed.

        iv.) Flash Memory

            - a special type of EEPROM.

            - erase whole memory electrically, per block or per chip erasable.

4.) Cache

   - small amount of fast memory.

   - Immediate buffer between normal main memory and CPU.

   - may be located on CPU chip or module

 

 Cache operation

a.) CPU requests contents of memory location.

b.) check cache for this data.

c.) if present, get from cache (fast) = Cache Hit.

d.) if not present, read required block from main memory to cache = Cache Miss.

e.) then deliver from a cache to CPU.

f.) cache include tags to identify which block of main memory is in each cache slot. 

  Direct, Associative and Set Associative Mapping

 Cache Replacement

 - When the address accessed by CPU is not in cache, access has to be made to main memory.

 - Along with the required word, the entire block is transferred to cache.

 - But if cache is full, some existing cache memory is deleted to create space for the new entry.

 - So some replacement algorithm is needed.

5.) Cache Write Policy

= must not overwrite a cache block unless main memory is up to date.

 Two cases to consider when block that is in cache needs to be updated:

      a.) Write through
            = write the result in both the main memory and cache.
 

      b.) Write back
            = write in cache memory only to minimize memory writes.

6.) Complementary Metal Oxide Semiconductor (CMOS)

  - CMOS memory requires very little power to retain its contents. Usually powered by a battery.

  - CMOS stores vital data about the configuration of the computer system, even when the computer is turned off.

7.)Types of External Memory

      a.) Magnetic Disk
           - RAID
           - Removable (floppy)

      b.) Optical
           - CD-ROM
           - CD-Recordable (CD-R)
           - CD-R/W
           - DVD

     c.) Magnetic Tape
           - Casette

Calculation part ( Direct, Associative, and Set Associative)

 

        

 

                                                                                                                        
                                                                                                 By  Teoh Soon Gi