Computer memory can be classified as primary or secondary memory. Primary memory, like RAM and ROM, holds data and instructions temporarily and is directly accessible by the CPU. RAM is volatile and stores active data, applications, and the operating system. ROM is non-volatile and stores basic startup instructions. Secondary memory, like hard disks, stores data permanently but is slower to access. It is used to store programs and data long-term, transfer data between computers, and back up information. Memory is measured in units like bits, bytes, kilobytes, and gigabytes.

1. Computer Memory
Memoryis a place where we can store data,instructionsandresultstemporarilyorpermanently.
Memorycan be classifiedintotwo:primarymemoryandsecondarymemory.Primarymemoryholds
data, intermediate resultsandresultsof ongoingjobstemporarily.Secondarymemoryonthe other
handholdsdata and informationpermanently.Before learningmore aboutmemory,letusdiscussthe
differentmemorymeasuringunits
BinaryDigit= 1 Bit 1 Nibble =4 Bits
1 Byte = 8 Bits 1 KB(KiloByte) = 1024 Bytes 1 MB (Mega Byte) = 1024 KB
1 GB (Giga Byte) = 1024 MB 1 TB (TeraByte) = 1024 GB 1 PB (PetaByte) = 1024 TB
Primary memory
Primarymemoryisa semiconductormemorythatisaccesseddirectlybythe CPU.It iscapable of
sendingandreceivingdataathighspeed.Thisincludesmainlythreetypesof memorysuchasRAM,
ROM andCache memory.
1 Random Access Memory (RAM)
RAM referstothe mainmemorythat microprocessorcanreadfrom and write to.Data can be stored
and retrievedatrandomfromanywhere withinthe RAM,nomatter where the datais.Data or
instructionstobe processedbythe CPU mustbe placedinthe RAM . The contentsof RAMare lostwhen
powerisswitchedoff.Therefore,RAMisa volatile memory.The storage capacityof RAMis2 GB and
above The speedof a RAMrefersto howfast the data inmemoryisaccessed.Itis measuredinMega
Hertz (MHz).Whena computeris inuse,itsRAMcontainsthe following:1.The operatingsystem
software. 2.The applicationsoftwarecurrentlybeingused.3.Anydatathat isbeingprocessed.
2. ReadOnly Memory (ROM)
ROM isa permanentmemorythatcan performonlyreadoperationsanditscontentscannotbe easily
altered.ROMis non-volatile;the contentsare retainedevenafterthe powerisswitchedoff.ROMis
usedinmost computerstoholda small,special piece of 'bootup'programknownas Basic InputOutput
System(BIOS).Thissoftware runswhenthe computerisswitchedonor'bootsup'. It checksthe
computer'shardware andthenloadsthe operatingsystem.ItisslowerthanRAM.
There are some modifiedtypesof ROMthat include:
1. PROM - Programmable ROMwhichcan be programmedonlyonce.PROMsare programmedat the
time of manufacture.

2. 2. EPROM - Erasable Programmable ROMthatcan be erasedusingultravioletradiationandcanbe
programmedusingspecial electroniccircuits.
3. EEPROM - ElectricallyErasable Programmable ROMwhichcanbe erasedandrewrittenelectrically
3 Cache memory
Cache memoryisa small andfast memorybetweenthe processorandRAM(mainmemory).Frequently
accesseddata,instructions,intermediateresults,etc.are storedincache memoryforquickaccess.
Whenthe processorneedstoread fromor write to a locationinRAM, itfirstcheckswhethera copyof
that data isin the cache.If so,the processorimmediatelyreadsthe cache,whichismuchfasterthan
readingfromRAM. Cache is more expensive thanRAM,butit isworthusingit inorderto maximise
systemperformance.Commonlyusedcache memoriesandtheircapacitiesare Level 1Cache (128 KB),
Level 2 Cache (1 MB), Level 3 Cache (8 MB) and Level 4 Cache (128 MB)
ComparisonbetweenRAMandROM
Secondary or Auxiliary memory
Secondarymemoryisof permanentnature.Unlike the contentsof RAM,the data storedinthese
devicesdoesnotvanishwhenpoweristurnedoff.Secondarymemoryismuchlargerinsize thanRAM,
but isslower.Itstoresprogramsand data butthe processor cannotaccess themdirectly.Secondary
memoryisalsousedfor transferringdataor programsfromone computerto another.It alsoacts as a
backup.The majorcategoriesof storage devicesare magnetic,optical andsemiconductormemory