RAM vs. CPU in Lightroom

Every couple of weeks, I get an email that asks:

What's more important RAM or CPU when running Lightroom?

The same question comes on regular basis on the various Lightroom forums. My answer is:

Spend your money on the fastest CPU you can and don't worry about the RAM!

Here is a screen capture of the Windows Task Manager. It's only running Lightroom. The Lightroom catalog is fairly standard with around 26,000 photos and 4,000 keywords. This Lightroom is still running under Windows XP on this computer. I have another Windows 7 computer with the same version of Lightroom and the same catalogue with very similar results, just Windows 7 takes much more memory but Lightroom runs at the same speed.

Lightroom: Task Manager: Ram & CPU Usage

Lightroom: Task Manager: Ram & CPU Usage

  1. The 2 CPUs are busy at 100%. It's all Kernel times. What's Kernel time? It's the time spent in the operating system, be it Windows or OSx, and not in the application like Lightroom! Most of the Kernel times are made of IO, input/outputs, and that includes memory IOs and disk IOs. After all the computer gobbledygook, in plain English, we have the reads and writes between the SQLite database, the photos on the disk, and Windows/OSx.

    This means that it's not Lightroom itself that runs the CPUs at 100% but Lightroom relying on the Windows/OSx functions. The green line on the top portion is the total CPU usage, it's also maxed out at 100%.

  2. The total memory usage is only 468 megabytes. This is made of the memory used by Lightroom, by Microsoft Windows, and by the antivirus. The Lightroom catalog is fairly typical around 26,000 photos with 4,000 keywords. Lightroom, itself, "only" uses 210Mb of RAM.

    • My recommendation is to get a computer with the fastest CPU you can afford, duh! I said the fastest1, not the biggest.

      There won't be much improvement in speed from going from a Core-2-Duo to a Quad-Core or a Six-Core, there will be some improvements, but the speed improvements will be minimal.

      On the other hand going from a 2.2Ghz CPU to a 3Ghz CPU will make a huge difference. My own test gave a 15% speed improvement. This was a completely unscientific test since too many variables were changed between the 2 computers.

    • Even on Windows 7, I still have to see Lightroom use more than 3 Gig of RAM, and those were huge catalogues of 200+ thousand photos.
  • In the 32 bit world, be it Microsoft Windows and Apple OSx, the maximum amount of usable memory is 3Gb. Not 100% true. It's possible to go past the 3Gb of memory by using PAE: Physical Address Extension
  • In the 64 bit world, with either Microsoft Windows 7 or Apple OSx, you can use more than 4Gb of RAM (in theory up to 128 Gig.) Not only the CPU has to be a 64 bit CPU, but Windows or OSx must also be 64 bit. And finally, you must also install Lightroom-64 bit.
  • Depending on the weather, the age of the captain and where the wind comes from, switching to 64 bit will give you a speed improvement from 15% to as much as 50%. Running Lightroom-32 bit on a Windows 7-64 bit or OSx-64 bit will be slower than Lightroom-32 bit on a Windows Vista-32 bit/Windows 7-32 bit or OSx-32 bit.
  • Lightroom is much more efficient than Photoshop. Photoshop, on the other hand, needs the biggest CPU a Six-Core is more important than CPU speed. Photoshop gobbles memory like no tomorrow. A Quad-Core i7 with 12 Gb RAM has become the standard computer (2011) for Photoshop CS5.

  1. Meaning the CPU clock speed.