Oracle allows you to have up to ten Archiver processes running for a single Oracle instance. However, unlike the case with multiple database writer processes, you don't need to manually specify the number of Archiver processes to run. The Log Writer process automatically invokes additional Archiver processes if the rate of change increases. When the rate of change slows again, the log writer process will terminate some of the extra Archiver processes.
If for some reason you want to exert manual control over the number of Archiver processes that run for a single instance, you can use the

LOG_ARCHIVE_MAX_PROCESSES

initialization parameter. Placing the following line in your initialization file will cause the instance to start with four Archiver processes:

LOG_ARCHIVE_MAX_PROCESSES=4

The name of the parameter is a bit misleading. Even though the word “MAX” is used, it really causes the instance to start with the specified number of Archiver processes.
As with the database writer, prior versions of Oracle did not allow multiple Archiver processes. The previous abbreviation for the archiver was ARCH, and you will still see that used in some books.

The archiver process (ARCn) copies redo log files to a designated storage device after a log switch has occurred. ARCn processes are present only when the database is in ARCHIVELOG mode, and automatic archiving is enabled. An Oracle instance can have up to 10 ARCn processes (ARC0 to ARC9). The LGWR process starts a new ARCn process whenever the current number of ARCn processes is insufficient to handle the workload. The alert log keeps a record of when LGWR starts a new ARCn process. If you anticipate a heavy workload for archiving, such as during bulk loading of data, you can specify multiple archiver processes with the initialization parameter

LOG_ARCHIVE_MAX_PROCESSES. 

The ALTER SYSTEM statement can change the value of this parameter dynamically to increase or decrease the number of ARCn processes. However, you do not need to change this parameter from its default value of 1, because the system determines how many ARCn processes are needed, and LGWR automatically starts up more ARCn processes when the database workload requires more.