How big should the RAM Disk size for the PCD Web Server be?

FAQ #100299

As big as possible...

In relation to the use of the Web Editor, it is important to choose the highest possible RAM Disk size of the PCD Web Server. A too small RAM Disk size may lead to the message "No Message: " instead of the value to be shown by the Web Editor applet.


What is the purpose of the RAM Disk?
A browser (or the java-applet running in the browser) is requesting PCD variables (PPO, e.g.registers, timers, flags etc.) using the CGI-functions "OrderVal.exe" and "ReadFile.exe". The requested items or files are stored in the ramdisk. Web project created with the Web-Editor are applying these functions.


Why should the RAM Disk size be set to the maximal size?
The size of the files stored in the ramdisk is depending on the amount of the PCD variables. If the ramdisk of the PCD Web Server is too small for holding all values of the PPOs used in a Web Server project, the result will be that not all PPO values will be sent on a request by the Web Editor applet. This will lead to the "No Message: [Unit of the PPO]" shown in the Web Browser. In this case the entry "WEB RAM TOO SMALL" will be written into the history of the PCD.
If too many PPOs are requested, systems equipped with older firmware versions than indicated in the table below even can crash!
The configured size of the ramdisk won't affect the performance of the PCD (or the memory available) in any way.


Firmware requirement
The maximal ramdisk size is depending on the PCD type. The maximal amount of PPOs that can be stored in the ramdisk is depending on the firmware (FW; Operating System of the PCD). Please refer to the following table that indicates the minimum FW version for the concerned PCD/PCS type.
Note that the amount of PPOs that can be stored on ramdisk (indicated in the last two columns) is only valid if there is only one file in the ramdisk (this is the case if the option "Order per view" is not checked!).

Minimal firmware for Web Server


PCD Type

maximal RAM disk size


minimal FW version


optimized FW version bigger than


32 [kByte]


010 (600 PPO max)

$18 (1500 PPO max)


32 [kByte]


020 (600 PPO max)

$22 (1500 PPO max)


32 [kByte]


017 (600 PPO max)

020 (1500 PPO max)


32 [kByte]



$C6 (1500 PPO max)


32 [kByte]



0A1 (1500 PPO max)


8 [kByte]


01A (100 PPO max)

BA5 (250 PPO max)

For the calculation of the maximal amount of PPOs the following formula was applied:
(Max ramdisk size)/20Byte = Amount of PPOs
20 bytes is an average size of a PCD media access (e.g. PDP,,R1000,d).


Where is the size of the ramdisk size configured?
The RAM Disc size is to be specified in the Web Builder that is used to generate the file downloaded to the PCD/PCS. In PG5 version up to SP1.3.110 the size of 4 kBytes is set by default (the Web Builder distributed together with later versions of PG5 will have a bigger default value) .
For accessing the settings for the RAM Disk size,

  • open the Web Builder
  • push the button "Settings..."
  • while the window Web-Server Settings is open, press the key <control> and type in "saia" (keep the Control-key pressed). </control>

Now you should see additional settings, among them also the parameter "RAM Disk size [kBytes]". In this field, enter the value listed in the table above for your CPU.

Don't edit a value bigger than listed in the table above; otherwise the FW will allocate the minimum value to the RAM Disk size (2 kByte).
After having changed this parameter, press the "OK"-button, generate your Web Server project and in PG5 Project manager, execute a "rebuild all" and then downlaod your project again.

If this doesn't fix the "No Message: ", please also refer to FAQs listed below:


Related Files:


Web Editor5

Last update: 01.06.2015 08:51

First release: 11.01.2005 19:00

Views: 6395

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