The Siemens 6ES5 374-2KH21 is a memory card designed for use with Siemens SIMATIC S5 programmable logic controllers (PLCs). It is a long-type memory card with a capacity of 256 kilobytes and operates on a 5V power supply.

Key features:

• Long-type design: The memory card has a longer physical length compared to standard-sized memory cards. This design is specific to certain SIMATIC S5 PLC models.
• 5V power supply: The card requires a 5V power supply for operation.
• Flash-EPROM technology: The memory card uses Flash-EPROM (Electrically Programmable Read-Only Memory) technology, which allows for multiple programming cycles and data retention even when the power is turned off.  
• 256 kilobytes capacity: The card has a storage capacity of 256 kilobytes, which can be used to store program data, configuration settings, and other information for the SIMATIC S5 PLC. 

Applications:

• Storing PLC programs: The memory card can be used to store the program code for the SIMATIC S5 PLC. This allows for easy program loading, modification, and backup.
• Configuration settings: The card can store configuration settings for the PLC, such as communication parameters, I/O assignments, and alarm settings.
• Data logging: The memory card can be used to store data collected by the PLC, such as process measurements, alarms, and historical data.

Additional information:

• Part number: 6ES5 374-2KH21
• Product family: SIMATIC S5
• Product description: Memory card long type 5V only Flash-EPROM, 256 KB 
• Product lifecycle: Discontinued product