Photoshop CS5 should run fast with 4GB ram right?

Is the machine sluggish in general? Have a look and see what other processes are running to see if anything else is hogging resources. (torrent clients and such, perhaps). Download Advanced System Care and Ccleaner (both are free) and give your machine a bit of house keeping. See if that helps.

This is kinda one of those 'how long is a piece of string' questions. It's impossible to tell without details of what you're doing, what you're trying to do it with, and what you're trying to do it ON.
IE, in work at the moment I have a machine with 8GB ram and an 8 core processor, and I can still regularly bring it to it's knees depending on what I'm doing.
If it's PS you're using to try and do this there are tons of performance tips and tricks to try and wring the most out of your hardware.
Could be though that you're just doing something that's so costly that it's making the machine fall over. I.E., how big are the files you're trying to merge ? Does the software load them all into memory simultaneously and try and process them ? Etc etc .

First.. the more RAM you can throw at it the better. This is one of the places where 64-bit can be very important.
A 32-bit version of Windows can "fake" using more than 4GB of ram using something called PAE... using PAE instead of native 64-bit addressing slows things down.
If PAE isn't turned on, then you're only getting 3.6G of that 4G of RAM in-use by the O/S.
With a 64-bit version, it gets accessed natively, without the PAE slowdown. (Page Address Extensions I think is what PAE means.. it has to "page" memory.. swapping parts of any memory above 4GB down below the 4GB mark, then swapping it back out when it's done with it... it's how my Commodore 64 managed to address 576KB of RAM back in the late 1980's)

Whether you have 32-bit running PAE or 64-bit native, getting more RAM (doubling or more) will speed things up considerably.

The deeper the bit-depth you're working with in your images, and the higher the overall resolution, the more RAM you need. If you're working with a 14MP image in 48-bit color with several layers, each of which has it's own alpha channel etc.. your image can actually become pretty enormous in RAM.

Also.. the more crap you can shut down while using Photoshop, the better. Don't run your e-mail program, or your web-browser etc.. JUST have Photoshop open.

The speed of your hard-drives can make a big difference as well, especially if you're working with images that are so large that parts of them get swapped out to disk. If you have a laptop, or really cheap, large hard drives, they might very well be only 5400RPM drives. Your drives are probably SATA, which isn't as fast for disk-writes as SAS or SCSI. A fair number of newer machines are coming with "near-line SAS" which is actually a SATA drive with a SAS interface on it.. not really SAS.
Try to make sure you have 7200rpm drives, or if you can afford it, get big, honking 15kRPM SAS drives.

In Windows, you can set a larger default swapfile size. This will pre-allocate the swapfile to be larger than what you will need, so that the operating system doesn't have to "grow" and "shrink" the swapfile to meet the RAM needs of an individual file.

Another thing to look at is the control within Photoshop that tells it how much RAM to allow itself to use. You want to keep this down to no more than 75-80% of total RAM.. and that's if you have nothing else running.

Disabling your virus-scanning software can make a big difference in saving files, and in swapping times for things that aren't the system swapfile. (Photoshop will create it's own "scratch" files.. and your anti-virus software may be scanning them on-the-fly while you're working..slowing things down considerably, especially if you have SATA or PATA drives.

and.. you might think about putting more RAM in it.

If you're running on a laptop, that might not be an option.. and you might not be able to swap out the hard-drive for something faster if it's a 5400, or even 3300 RPM drive. (some laptops have drives that slow.)
If looking at drive transfer rates.. try & find the rates for to/from the platters.. most drives "advertised" transfer speeds are actually for transfers from the buffer in the drive to RAM, and have nothing to do with the actual disk speed.

Did I mention that more RAM might help?

not 576MB... 576KB.. you're off by an order of magnitude.. I had a half a MEG of ram... which was astounding in it's day. I did desktop publishing with a full GUI on it. (GEOS with GeoPublish.. along with everything else available for GEOS at the time... I even had a real analogue mouse & everything.) But.. GeoPaint was never a Photoshop competitor!

DaireQuinlan wrote: »

Hang on a second, you had a C64 with HALF A GIG OF RAM ?!?!?!?

Magicland Dizzy must have been very dizzy with all that raw power