On formation in August 1914, I Reserve Corps consisted of two divisions, made up of reserve units. In general, Reserve Corps and Reserve Divisions were weaker than their active counterparts
Reserve Infantry Regiments did not always have three battalions nor necessarily contain a machine gun company
Reserve Jäger Battalions did not have a machine gun company on formation
Reserve Cavalry Regiments consisted of just three squadrons
Reserve Field Artillery Regiments usually consisted of two abteilungen of three batteries each
Corps Troops generally consisted of a Telephone Detachment and four sections of munition columns and trains 
In summary, I Reserve Corps mobilised with 26 infantry battalions, 11 machine gun companies (66 machine guns), 6 cavalry squadrons, 12 field artillery batteries (72 guns) and 2 pioneer companies. 1st Reserve Division was particularly strong in machine gun formations as the 1st, 3rd and 18th Reserve Infantry Regiments all had two machine gun companies. 36th Reserve Division was formed by units drawn from the XVII Corps District. It included one active Infantry Regiment (54th).
On mobilisation, I Reserve Corps was assigned to the 8th Army on the Eastern Front, intended to defend East Prussia while the rest of the German Army executed the Schlieffen Plan offensive against France.
I Reserve Corps had the following commanders during its existence:
^Cron 2002, p. 111 About a third of Reserve Infantry Regiments formed in August 1914 lacked a machine gun company
^Cron 2002, p. 116 Active Jäger Battalions had a machine gun company with the exceptions of the 1st and 2nd Bavarian Jäger Battalions
^Cron 2002, p. 128 Most active cavalry regiments had four squadrons, some were raised to six squadrons
^Cron 2002, p. 134 Active Divisions had a Field Artillery Brigade of two regiments
^Cron 2002, p. 86 Active Corps Troops included a battalion of heavy howitzers (Foot Artillery), an Aviation Detachment, a Telephone Detachment, a Corps Pontoon Train, a searchlight section, 2 munition column sections, one Foot Artillery munitions column section and two Train sections
Cron, Hermann (2002). Imperial German Army 1914-18: Organisation, Structure, Orders-of-Battle [first published: 1937]. Helion & Co. ISBN1-874622-70-1.
Ellis, John; Cox, Michael (1993). The World War I Databook. Aurum Press Ltd. ISBN1-85410-766-6.
Histories of Two Hundred and Fifty-One Divisions of the German Army which Participated in the War (1914-1918), compiled from records of Intelligence section of the General Staff, American Expionary Forces, at General Headquarters, Chaumont, France 1919. The London Stamp Exchange Ltd (1989). 1920. ISBN0-948130-87-3.
The German Forces in the Field; 7th Revision, 11th November 1918; Compiled by the General Staff, War Office. Imperial War Museum, London and The Battery Press, Inc (1995). 1918. ISBN1-870423-95-X.