Scalable Software Architecture

n sftwr ngnrng, mlttr rchtctr (ftn rfrrd t s n-tr rchtctr) s clnt–srvr rchtctr n whch prsnttn, pplctn prcssng nd dt mngmnt fnctns r physclly sprtd. Th mst wdsprd s f mlttr rchtctr s th thr-tr rchtctr (fr xmpl, Csc's Hrrchcl ntrntwrkng mdl). N-tr pplctn rchtctr prvds mdl by whch dvlprs cn crt flxbl nd rsbl pplctns. By sgrgtng n pplctn nt trs, dvlprs cqr th ptn f mdfyng r ddng spcfc tr, nstd f rwrkng th ntr pplctn. N-tr rchtctr s gd ft fr smll nd smpl pplctns bcs f ts smplcty nd lw-cst. ls, t cn b gd strtng pnt whn rchtctrl rqrmnts r nt clr yt. thr-tr rchtctr s typclly cmpsd f prsnttn tr, lgc tr, nd dt tr. Whl th cncpts f lyr nd tr r ftn sd ntrchngbly, n frly cmmn pnt f vw s tht thr s ndd dffrnc. Ths vw hlds tht lyr s lgcl strctrng mchnsm fr th cncptl lmnts tht mk p th sftwr sltn, whl tr s physcl strctrng mchnsm fr th hrdwr lmnts tht mk p th systm nfrstrctr. Fr xmpl, thr-lyr sltn cld sly b dplyd n sngl tr, sch n th cs f n xtrm dtbs-cntrc rchtctr clld RDBMS-nly rchtctr r n prsnl wrksttn.