Windows Embedded for HP Thin Clients - Write Filter Best Practices

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RAM
The total RAM of a thin client is generally divided into 4 functions:
• Main system memory
• RAMDisk
• Write filter overlay/cache
• Dedicated video memory (if a thin client does not have a discrete video card)
Main system memory
This is where all application and operating system processing occurs (similar to any Windows operating system).
Caution
Windows Embedded operating systems are not designed for use with a page file. Using a page file on an HP thin client is
unsupported. It will also significantly decrease the lifespan of the flash drive.
RAMDisk
The RAMDisk is a section of RAM used for write data of a temporary nature, such as most operating system-related writes.
On HP thin clients, the RAMDisk appears as the Z: drive by default.
By default, the Temporary Internet Files and TEMP folders are redirected to the Z: drive, as are Windows logs and the print
spooler. This keeps the write filter overlay/cache from filling up and enhances system security since the RAMDisk is cleared
every reboot. The Temporary Internet Files folder is a favored place for viruses to land, and because it is cleared at every
reboot, the threat is removed. The redirection also enhances performance since the read/write times for the RAM are much
faster than for the flash drive. These folders continue to be redirected even if the write filter is turned off.
Write filter overlay/cache
A section of RAM is dedicated to storing write data that was intercepted by the write filter. This section of RAM is called
either an overlay or cache, depending on the write filter you are using. Write data in the overlay or cache can be committed
to the flash drive using the write filter GUI or command line, or it can be discarded by rebooting the system.
Caution
Free space in the overlay or cache can eventually run out. HP highly recommends doing a regular maintenance reboot to
flush the stored write data.
Dedicated video memory
If a thin client does not have a discrete video card, the system makes use of Unified Memory Architecture (UMA), which
allows a section of RAM to be dedicated exclusively to video operations. The amount of memory dedicated to UMA is set in
the BIOS and takes effect in the chipset before the operating system boots. This memory is excluded from usable system
memory resources.
If a thin client has a discrete video card, then no additional RAM is used.