Glossary
SIMATIC Rack PC 847B
Operating Instructions, 06/2008, A5E02203168-01
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NEC Class 2
The "NEC", National Electrical Code, is the USA collection of regulations that generally
correspond to German VDE 0100 standards. All USA standards governing the safety of
electrical equipment and corresponding "deviations" in IEC standards are based on NEC in
terms of their country-specific requirements.
NEC Class 2 specifies higher safety requirements for protection against electric shock and
National Fire Protection Association (NFPA) requirements for fire protection. Power supplies
operating within the range from 20 VDC to 30 VDC must be equipped with an internal current
limiting circuit which safely prevents output power higher than 100 VA.
Operating system
Generic term which describes all functions for controlling and monitoring user program
execution, distribution of system resources to the user programs and the operating mode in
cooperation with the hardware (for example Windows XP Professional).
Packet writing
The CD-RW is used as a disk medium. The CD can then be read only by packet–writing
compatible software or has to be finalized. Finalization of a CD closes the CD within an
ISO9660 shell. You can still write to the CD-RW several times in spite of finalization. Not all
CD drives can read packet-written CDs . There are restrictions to using this method in
general data transfer.
PATA
Interface for hard disk drives and optical drives, with parallel data transmission rate up to 100
Mbps.
PC card
Trademark of the Personal Computer Memory Card International Association (PCMCIA).
Designation for auxiliary cards that conform with PCMCIA specifications. A PC card that has
roughly the size of a credit card can be plugged into a PCMCIA slot. Version 1 specifies
cards of Type I with a thickness of 3.3 millimeters, which are designed mainly for use as
external memory. Version 2 of the PCMCIA specification also defines cards of Type II with a
thickness of 5 mm and cards of Type III with a thickness of 10.5 mm. Type II cards can
realize devices such as modems, fax cards and network interface cards. Type III cards are
equipped with devices that require more space, for example wireless communication
modules, or rotary storage media such as hard disk drives, for example.
PC/104 / PC/104-Plus
Two bus architectures are especially fashionable today in the industrial world. PC/104 and
PC/104-
Plus. Both are standard in single-board computers of the PC class. The electrical
and logical layout of the two bus systems is identical with ISA (PC/104) and PCI (PC/104-
Plus). Software cannot usually detect a difference between them and normal desktop bus
systems. Their advantage is the compact design and the resulting space they save.
