Compiled Military Service Records (CMSR)

Each volunteer soldier has one Compiled Military Service Record (CMSR) for each regiment in which he served. An index is available online at the Civil War Soldiers and Sailors System website or on microfilm at selected NARA facilities and large genealogical research libraries. The CMSR contains basic information about the soldier's military career, and it is the first source the researcher should consult. The CMSR is an envelope (a jacket) containing one or more cards.** These cards typically indicate that the soldier was present or absent during a certain period of time. Other cards may indicate the date of enlistment and discharge, amount of bounty paid him, and other information such as wounds received during battle or hospitalization for injury or illness. The soldier's place of birth may be indicated; if foreign born, only the country of birth is stated. The CMSR may contain an internal jacket for so-called "personal papers" of various kinds. These may include a copy of the soldier's enlistment paper, papers relating to his capture and release as a prisoner of war, or a statement that he had no personal property with him when he died. Note, however, that the CMSR rarely indicates battles in which a soldier fought; that information must be derived from other sources.

https://www.archives.gov/research/military/civil-war/resources.html

** These are legal size envelopes containing all the ~ 3-1 x 8-1/2” cards.
At the National Archives these envelopes are not available for viewing, instead, they have all been microfilmed and this is what a visitor will view and make copies from. However, if can convince one of their clerks that the information copied from the machine is un-readable, they will pull the individual records which you can view in a reading room and where you can xerox.

What you will receive from a service provided by these Message boards are xerox copies of these cards, presented, I believe, 3 cards per sheet.