The OP's original post stated:
1) New computer will come with 4GB RAM
2) OP intends to upgrade to 8GB RAM (eventually)
Then asked:
Will it "run ok" in 4GB?
The answer is: Yes, it will run. But if you want optimal performance then you should do that upgrade to 8GB whenever possible.
I'm staring at the memory allocation by process. When I launch Lightroom it wants roughly 1GB of RAM and if I just work with one image it'll grow that size a little.
As I start browsing images in the Library module I can see it starting to grab a lot more RAM and it can easily grab a couple GB within a few minutes. I have a lot of images and my images are all stored on external storage arrays (because I'd run out of disk space if I kept them on the internal drive). The large number of images probably eats through more memory as I browse my images in the Library module of Lightroom.
However... I was using it yesterday to work on just a handful of images (one at a time) and looked over at the resource consumption ... and noticed that Lightroom had claimed 5.8GB of RAM (I hand't been using Lr for that long... perhaps 15 minutes.) The point being... if Lightroom has the memory, then it will use it.
I'm not sure what Lr does when it "wants" nearly 6GB and it's on a machine that only "has" 4GB (especially considering that Windows itself will want a healthy chunk of RAM of it's own.) This would normally mean it can't use caches for performance and/or the OS will have to start "paging" processes out to make memory available. I don't have a 4GB machine to test it. But I do have extensive experience in OS tuning. One fundamental rule when configuring a computer for a given task is that you
size that machine
for that task. I haven't seen Lightroom go beyond 6GB since I've been watching it (my desktop machine has 32GB so if it wanted the RAM, it's certainly available.) But given that the OS is going to need memory of it's own, the 8GB "recommendation" by Adobe certainly makes sense.
Memory is cheap. A single 4G module seems to be around $32 but if you buy more than one you tend to get a break. e.g. an 8GB "kit" which really consists of 2x 4GB modules is probably less than $60 (I'm checking one source and it's showing me $58 -- but the real price would depend on the type of memory and the source.)
A 4GB computer might come with a single 4GB memory module, or it might come with 2 x 2GB modules. Some computers will do something called "memory interleave". If your hardware supports this then you want to make sure that you build up memory banks with IDENTICAL memory modules. If the hardware supports "memory interleave" and you want 8GB of RAM then you'll get better performance using 2 x 4GB modules then you will using 1 x 8GB module. As mentioned earlier, computers break down memory into manageable "pages" and a "page" is the smallest unit of memory that can be allocated (if a computer program only uses a few bytes of memory, what it will get is a full "page" of memory). the pagesize depends on the hardware (4k is a common size). Non-interleaved memory means that the memory pages are sequential on a single memory module until that module is "full" and then it moves on to the next module. "Interleaved" memory means that it puts all the odd number pages on one module and the even number pages on the other module (of the pair). This allows the machine to access memory to/from both modules "in parallel" so it speeds up memory access for applications that plan to use a lot of RAM. If the memory modules are not identical then the computer will still work -- it just won't use "memory interleave" (it only works if the memory is identical.)
Will it work with 4GB? Without a doubt it will. BUT... if you want it to "perform" then you go with the "recommended" RAM size. That size is 8GB and it's listed here:
System requirements for Photoshop Lightroom for Mac and Windows OS
If you don't want to buy the 8GB on day #1 then just use the 4GB because it will work. Your computer is not going to be crashing... it'll deal with the limited memory situation. It just won't be "as fast" as a machine with 8GB. (But remember... RAM is cheap!)
To be fair... a few years ago I switched from using the typical hard drives (rotating platters) to Solid State Drives (SSD) and
that made
far more of a performance difference than anything. My external storage arrays are 4TB each -- so converting them to SDD would be expensive (also you don't want to insert anything into a storage array that isn't "certified" and almost no storage arrays "certify" SSDs -- but I haven't re-checked in the past year.) SSDs have come way down in price, but they're still expensive. If you really want things to scream along.... this would probably be the single most noticeable performance upgrade (it just won't be cheap.)
