MachineinstructionsareinstructionsthattheCPUcandirectlyrecognizeandexecute,andtheirmanifestationsarebinarycodes.Amachineinstructionisusuallycomposedofanopcodeandanoperand.Theopcodeindicatestheoperationtobecompletedbytheinstruction,thatis,thefunctionoftheinstruction,andtheoperandindicatestheobjectinvolvedintheoperation,andthelocationwheretheresultoftheoperationisstored.
BecausemachineinstructionsarecloselyrelatedtoCPUs,differenttypesofCPUscorrespondtodifferentmachineinstructions,andtheirinstructionsystemsareoftenverydifferent.ButforthesameseriesofCPUs,inordertomeetthegoodcompatibilitybetweenvariousmodels,itisnecessarytodo:theinstructionsystemofthenewgenerationCPUmustincludetheinstructionsystemofthepreviousCPUofthesameseries.OnlyinthiswaycanthevariousprogramspreviouslydevelopedrunnormallyonthenewgenerationofCPUs.
Machinelanguageisusedtodirectlydescribemachineinstructions,rulesforusingmachineinstructions,etc.ItistheonlylanguagethattheCPUcandirectlyrecognize,thatis,theCPUcandirectlyexecuteprogramsdescribedinmachinelanguage.
Writingprogramsinmachinelanguageistheworkofearlyprofessionalandtechnicalpersonnelwhohavebeenrigorouslytrained.Ordinaryprogrammersaregenerallydifficulttodo.Moreover,programswritteninmachinelanguagearenoteasytoread,havehigherrorrates,andaredifficulttomaintain.Cannotdirectlyreflectthebasicideaofusingcomputerstosolveproblems.
Becauseoftheaboveinconveniencesofwritingprogramsinmachinelanguage,almostnoprogrammerswriteprogramslikethis.