How did the gulag system differ from the concentration camps

 was the government agency that administered the main Soviet forced labor camp systems during the Stalin era, from the 1930s until the 1950s. The first such camps were created in 1918 and the term is widely used to describe any forced labor camp in the USSR.[1] While the camps housed a wide range of convicts, from petty criminals to political prisoners, large numbers were convicted by simplified procedures, such as NKVD troikas and other instruments of extrajudicial punishment (the NKVD was the Soviet secret police). The Gulag is recognized as a major instrument of political repression in the Soviet Union, based on Article 58 (RSFSR Penal Code). The term is also sometimes used to describe the camps themselves, particularly in the West. 

"GULAG" was the acronym for Гла́вное управле́ние лагере́й (Glavnoye upravleniye lagerey), the "Main Camp Administration". It was the short form of the official name Гла́вное управле́ние исправи́тельно-трудовы́х лагере́й и коло́ний (Glavnoye upravleniye ispravityelno-trudovykh lagerey i koloniy), the "Main Administration of Corrective Labor Camps and Labor Settlements". It was administered first by the GPU, later by the NKVD and in the final years by the MVD, the Ministry of Internal Affairs. The first corrective labour camps after the revolution were established in 1918 (Solovki) and legalized by a decree "On creation of the forced-labor camps" on 15 April 1919. The internment system grew rapidly, reaching population of 100,000 in the 1920s and from the very beginning it had a very high mortality rate.[2] 

Forced labor camps continued to function outside of the agency until late 80s (Perm-36 closed in 1988). A number of Soviet dissidents described the continuation of the Gulag after it was officially closed: Anatoli Marchenko (who actually died in a camp in 1986), Vladimir Bukovsky, Yuri Orlov, Nathan Shcharansky, all of them released from the Gulag and given permission to emigrate in the West, after years of international pressure on Soviet authorities. 

Aleksandr Solzhenitsyn, who spent eight years of Gulag incarceration, winner of the 1970 Nobel Prize in Literature, gave the term its international repute with the publication of The Gulag Archipelago in 1973. The author likened the scattered camps to "a chain of islands" and as an eyewitness described the Gulag as a system where people were worked to death.[3] Some scholars support this view,[4][5] though it is controversial, considering that with the obvious exception of the war years, a very large majority of people who entered the Gulag left alive.[6] In March 1940, there were 53 Gulag camp directorates (colloquially referred to as simply "camps") and 423 labor colonies in the USSR.[7] Today's major industrial cities of the Russian Arctic, such as Norilsk, Vorkuta, and Magadan, were originally camps built by prisoners and run by ex-prisoners.[8]

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