100 Gb of free space is not very much to be shared by the swap files of the OS and Photoshop's scratch disk file.
Also, you have not given us any clues as to how many other applications are running at the same time, how many image files you have open in Photoshop, what platform you are on, Macintosh or Windows, machine specs, exact versions of the OS and Photoshop, which version of the graphics driver, amountof VRAM on the video card, wheher Open GL is enabled etc.
Please read this FAQ for advice on how to ask your questions correctly for quicker and better answers:
I am running Windows 8 with the latest updates and Photoshop CS6 with the lates updated aswell. Precice system specs you will find below.
I closed all foreground and background programs and had only photoshop open.
Also I played around with the performance settings in Photoshop, also disabling GPU acceleration, without any success.
Operating System: Windows 8 Pro 64-bit (6.2, Build 9200) (9200.win8_gdr.130306-1502)
Processor: Intel(R) Core(TM) i7 CPU Q 820 @ 1.73GHz (8 CPUs), ~1.7GHz
Memory: 8192MB RAM
Page File: 3318MB used, 12996MB available
Card name: NVIDIA Quadro FX 880M
Display Memory: 4562 MB
Dedicated Memory: 978 MB
Shared Memory: 3583 MB
Adobe Photoshop Version: 13.0.1 (13.0.1 20120808.r.519 2012/08/08:21:00:00) x64
Operating System: Windows NT
System architecture: Intel CPU Family:6, Model:14, Stepping:5 with MMX, SSE Integer, SSE FP, SSE2, SSE3, SSE4.1, SSE4.2, HyperThreading
Physical processor count: 4
Logical processor count: 8
Processor speed: 1729 MHz
Built-in memory: 8124 MB
Free memory: 5337 MB
Memory available to Photoshop: 7149 MB
Memory used by Photoshop: 63 %
Image tile size: 128K
Image cache levels: 4
OpenGL Drawing: Enabled.
OpenGL Drawing Mode: Advanced
OpenGL Allow Normal Mode: True.
OpenGL Allow Advanced Mode: True.
OpenGL Allow Old GPUs: Not Detected.
Video Card Vendor: NVIDIA Corporation
Video Card Renderer: Quadro FX 880M/PCIe/SSE2