Where can I download the Disk Speed Utility

I have looked everywhere, where can I get a copy of the disk speed utility? Is there even a windows version?

Two options:
1/ You can run the utilities already installed in the C:\Program Files\Blackmagic Design\DaVinci Resolve folder. In addition to TestIOWin.exe, you'll find bandwidthTest.exe for your graphic card.
2/ You can install the desktop video drivers for BMD capture hardware. The disk speed test will get installed too and will run even if you don't have any capture hardware.

Thanks, I have found the files however when I double click on TestIOWin.exe i see the briefest flash of what looks like a command line box and then nothing happens. Do I need to add a command line switch?
I'm using Win 7 Ultimate 64.

Yes, the easiest way to do it is to click on the Start Menu, then in the Start Search Box, type Run. In the Open box, you need to type the complete path. For instance:
c:\program files\blackmagic design\davinci resolve\bandwidthTest.exe

If you're having trouble with this, just let me know and I'll give a more detailed answer tonight (CET). The other option is to install the desktop video drivers in order to get a utility with a simple user interface.

OK, so let's reorder what's available for Windows users:
1/ Try the easy-to-use software that goes with BMD video hardware drivers.
2/ If the read/write speed doesn't explain the lack of real-time playback, and you aren't familiar with the Command Prompt, then here's the list of switches to add after bandwidthTest.exe and TestIOWin.exe:

--help Display this help menu
--csv Print results as a CSV
--device=[deviceno] Specify the device device to be used
all - compute cumulative bandwidth on all the devices
0,1,2,...,n - Specify any particular device to be used
--memory=[MEMMODE] Specify which memory mode to use
pageable - pageable memory
pinned - non-pageable system memory
--mode=[MODE] Specify the mode to use
quick - performs a quick measurement
range - measures a user-specified range of values
shmoo - performs an intense shmoo of a large range of values
--htod Measure host to device transfers
--dtoh Measure device to host transfers
--dtod Measure device to device transfers
--wc Allocate pinned memory as write-combined
--cputiming Force CPU-based timing always
Range mode options
--start=[SIZE] Starting transfer size in bytes
--end=[SIZE] Ending transfer size in bytes
--increment=[SIZE] Increment size in bytes

Blackmagic Design Disk IO benchmark program - Version 1.0.4847
Usage: testiowin.exe <diskPath> <FrameSize in MB, 1,000,000 bytes> <Num Of Frames> <Number of Threads> <keep_cpu_busy> <Use Direct IO>
Examples:
testiowin.exe /dvt4/ 12.754 100 6 1 0
testiowin.exe /dvt4/ 12 100 1 0 0
[READ_ONLY_TEST] Usage: testiowin.exe <diskPath> <FrameSize in MB, 1,000,000 bytes> <Num Of Frames> <Number of Threads> <keep_cpu_busy> <Use Direct IO> <ClipPattern> <Start Frame>

That's the whole list just in case you require something special, but there's no need to be frightened. You can just check little things, like for instance if you have "PASSED" at the end of the bandwidth test.