Thse applications tend to "Bypass" the normal OS -- usually to avoid any overhead in using OS processes. They also interact directly with the main hardware too.
These are very specialized applications. However things like MS office and 90% of what most people tend to run on their machines with the exception of Virtual Machines the REAL RAM will be managed by the OS and you probably won't see it taking too much of it at all unless running LOADS of concurrent applications.
This is why even a 2GB RAM machine is often more than sufficient for the vast majority of "Normal" computer users.
System Manufacturer/Model Number Custom built OS W7 X-64 RTM,SUSE 11.1, XP PRO SP3 as a VM, VMware ESXi CPU Q9400 QUAD Motherboard P5QL-CM Memory 8GB Graphics Card On Motherborad Sound Card Realtek HD audio Monitor(s) Displays Apple Cinema display
Mouse Toshiba wireless laser Hard Drives 4 X 1TB SATA Internet Speed > 20MB up
A lot of photoshop operations write to its scratch disk no matter how much memory you have. For instance, if you convert a layer to a smart object it will write hundreds of MB to its scratch disk. Unless you have your scratch disk on an SSD with very fast writes, this takes 5 seconds, you can sit there and watch it! So I suspect something like that is happening. You can monitor the scratch disk for activity to see if the is the culprit.
Another example. I can write full speed to my scratch disk at about 100 MB/s. I have photoshop configured to use up to 5 of my 8 GB of memory. I just opened up a 10MP RAW image in PS CS5. That wrote about 100 MB to my scratch disk for about 1 second. I duplicated the layer. Another 100MB and 1 second to complete. I then smart sharpened the image. The scratch space jumped up 370 MB more or about 4 seconds to do the sharpening because of this. I am sure the sharpening itself takes no time, it is the writing to disk that does.
It is a real disappointment.
If I had the extra cash right now, I would get one of the new Intel 510 SSD explicitly for use as cache for Photoshop scratch, ACR and Bridge Cache, and Browser Cache. Maybe I would make it my system disk. But you need something that can do much better than HDD write speeds (>> 100MB/s) to see the difference. Many SSDs do not have write speeds that are any better than Hard disk drives. the Intel 510 claim to.
I should add how this relates to memory (I was addressing your "lag" above). I think Photoshop decides something is too big for RAM and writes it to its scratch disk - using les memory in the process/
Computer type PC/Desktop System Manufacturer/Model Number Home built (GeneO industries)/Model 3 OS Windows 7 64 bit SP1 CPU i5 2500k @ 4.5 GHz, 1.264V 124 GFlop (IBT with AVX) Motherboard ASUS P8Z68-V PRO/GEN3 Memory 16GB (4GBx4) 1600MHz G.skill Ripjaws X 8-8-8-24 Graphics Card MSI GTX 660 Ti PE/OC, 2GB 7160 MHz DDR5 clock, 1228 Mhz Core Sound Card Onboard Realtek HD Monitor(s) Displays NEC Spectraview 2490WUXi-SV Screen Resolution 1920 x 1200
Keyboard HP Wireless Mouse HP wireless PSU Seasonic X-850 (2012 KM3 model) Case Fractal Design "Define R3" Cooling CM TPC 812 push/pull, 3 120mm, 2 TY-140 case fans Hard Drives Samsung 128GB 840 Pro SSD (System), Crucial 128GB M4 SSD, 2x WD Caviar 1TB Black internal (data), 1x WD Blue 6Gb/s 1TB Internal, 1x 2TB eSata WD20EARS Green, 2x 500GB Seagate external USB, 1x 350GB exte Internet Speed 27.8 Mb/s down, 5.6 Mb/s up Other Info USB 3.0 x4 , SATA III x4, eSATA x3, SATA II x4, USB 2.0 x8. 2 Samsung DVD R/W drives.
WEI: CPU 7.7, Memory 7.8, Graphics 7.9, Disk 7.9