Hi stone576, 

Optiplex 755 has four variants:

1. Ultra small form factor
2. Small form factor
3. Desktop
4. Mini-tower

Please share the exact system model. 

The Optiplex 755 system supports up to 8 GB of memory with a 64 bit operating system and up to 4 GB of memory with a 32 bit operating system. The memory speeds supported include 667 and 800 MHz DDR2 memory. Both dual-channel and single-channel configurations are supported.

Recommended memory configuration would be to install a memory module in connector CHA_DIMM or a pair of matched memory modules installed in connectors CHA_DIMM and CHB_DIMM  

Note: Use non-ECC memory modules only as ECC modules are not supported.

Ensure to install a single memory module in CHA_DIMM, the connector closest to the processor, before installing a module in the other connector.

In reference to processor upgrade, Dell has only tested Optiplex 755 with the Intel Core2 Quad, Core2 Duo, Intel Pentium dual-core, Intel Celeron processors based on Intel's 775-pin (LGA775) socket. You may check a table below for the processors shipped with Optiplex 755 desktops:

Optiplex 755 is shipped with Intel Q35 (ICH9DO) chipset. For more information on this, you may refer to the link: http://intel.ly/SNTI4O 

Click on the compatible products to get the list of processors compatible with your computer. Please ensure to update system BIOS before you upgrade the processor on computer.  

For detailed installation of memory and processor on your computer, you may refer to the manuals of computer from links: http://bit.ly/ZXm4Kg and http://bit.ly/14rmWMD Ensure to follow safety instructions in manual. 

Please reply for further clarifications. 

Hi, chinmay s thank you for replying. I have mini tower with a Pentium d. So if I get any core 2 quad it will work? And I have windows 7 32 bit, but I'm gonna get a 64 bit and I was wondering if I put 8 gigs or ram will the operating system still work? Thank you so much for your answer.  

Sencerly, stone

Hi stone576, 

You may check the list of processors we have tested with Optiplex 755 in the previous post. Alternatively, you may find a list of compatible processors from the Intel website. A link for the same is shared in the previous post. Your system is shipped with a Intel Q35 chipset that supports maximum RAM of 8 GB. 

32-bit Windows Operating Systems allow maximum usage upto 4 GB RAM. 64-bit Windows allows the computer to overcome that limitation; recognizes RAM beyond 4GB. If you upgrade operating system to 64 bit, you might be able to upgrade memory to 8 GB. 

In reference to operating system, Dell has tested Optiplex 755 only with Windows XP and Vista. Drivers for same are available on support website. In case you are able to install Windows 7 64-bit on your computer, you may face challenges in finding the drivers for Windows 7 64 bit. As an alternate, you may try to install drivers for Vista 64 bit (might work) or may try to install in compatibility mode for Vista. If that does not work, you may need to check device manufacturer's website for the Windows 7 64-bit drivers (If available). 

Please reply for further clarifications.

hey i have a dell 755 as well its the desktop one (second largest)  i was wondering if its compatible with the

E5420

i know this is a xeon and i know other xeons can work but will this one im currently using a e6550 !  64bit with 4gb ram 1gb graphics card