Siemens 620 appendix Memory Cache Submenu, Write Back

Configuring the SIMATIC Box PC 620

”Memory Cache” Submenu

The following pop-up menu appears when you select the submenu “Memory cache” in the main menu:

		PhoenixBIOS Setup Utility
Main
System Time:		[ 15:35:32 ]			Item Specific Help
System Date:		[ 03/12/2002 ]
Diskette A:		[1.44 MB, 31/2” ]			Controls caching of
Primary Master		[20496 MB]			system conventional
					memory and memory
Primary Slave		[None]
					above one megabyte.
Secondary Master		[CD–
Secondary Slave		[None]	Disabled
			Write Through
Memory Cache:		[Write	Write Back
Boot Options
Keyboard Features
Hardware Options
System Memory:		640 KB
Extended Memory:		121856 MB
F1	Help	Select Item	+ / –	Change Values		F9	Setup Defaults
ESC	Exit	Select Menu	Enter	Select	Sub-Menu	F10	Save and Exit

Figure 5-4 “Memory Cache” Field

A cache is a fast memory buffer between the CPU and main memory (DRAM). Recurrent memory access operations are executed in the fast cache, instead of the main memory, if the function is enabled. In rare instances involving some hardware and software combinations, it may be necessary to disable the cache because the program runtimes or waits are too short on account of the fast cache.

[Disabled]	Cache is disabled
[Write Through]	Write access is not concluded until the entry has been made in main
	memory
[Write Back]	Write access is concluded immediately; the entry in main memory
	takes place in the backround (default)

SIMATIC Box PC 620 Manual	5-9
A5E00131465-01