Siemens SIMATIC Rack PC 840 V2 Operating Instructions Manual page 125

In the 32-
bit IO field
Option
"Transfer
Mode" and
"Ultra DMA
Mode"
Memory Cache field
If the "Memory Cache" field is selected in the main menu, the following context menu
appears:
Figure 16-7
The cache is a high-speed memory buffer between the CPU and memory (DRAM). When
the function is enabled, repeated memory accesses are executed in the faster cache, rather
than in the main memory. In rare cases it can be necessary to switch off (disable) the cache
for some hardware and software, as required program runtimes or pauses may be shortened
by the fast cache memory.
[Disabled]
[Write Through]
[Write Back]
SIMATIC Rack PC 840 V2
Operating Instructions, Edition 05/2006, A5E00248055-04
The access type for the drive is determined in the 32 Bit–I/O field
Disabled 16-bit accesses
Enabled 32-bit accesses (default)
The settings in these fields define the interface data transfer rate. The value is
dependant on the drive used and and should only be set with the Type field set to
"Auto".
You can exit the sub-menu with the ESC key.
"Memory Cache" field
Cache is disabled
Write access is not concluded until the entry has been made in main memory
Write access is concluded immediately, the entry in main memory takes
place in the background (default)
Detailed descriptions
16.5 BIOS Setup
16-27