I had Windows 7 32bit and minecraft was working... well enough, but since I upgraded to 64bit it barely gets to 30 fps sometimes. And I don't understand why cause now I'm even giving it more ram than when I was playing on 32bit. Yes I have optifine with everything turned down. Yes, I have tried allocating the same amount I was giving it when I was on 32bit, it runs worse.
Also been walking with F3 open and minecraft doesn't seem to use more then 400mb even if I gave it 2gb.
My pc Is old(2008) but I still had constant 30 fps with the help of optifine. Here are my specs:
Cpu: AMD Athlon LE-1640
Gpu: ATI Radeon HD 3400
If you have any idea what it could be please help.
64 bit does not necessarily improve performance, it may even worsen it, and with just 4 GB of RAM you aren't even gaining any additional memory, probably even losing memory due to 64 bit requiring more (and allocating 2 out of 4 GB is way too much - reduce that to 1 GB or even less - you should not allocate more than half your free memory to the game as the JVM uses more memory than what F3 shows):
The performance difference comparing an application running on a 64-bit platform versus a 32-bit platform on SPARC is on the order of 10-20% degradation when you move to a 64-bit VM. On AMD64 and EM64T platforms this difference ranges from 0-15% depending on the amount of pointer accessing your application performs [this is especially true for modern versions of Minecraft, which allocate incredible numbers of small objects].
The default heap size for all 32-bit J2SE implementations is 64MB. We have adjusted the defaults for 64-bit implementations to be 30% larger in order to make up for the increased size of Java objects due to larger native pointers.
Also, looking at the specs for your CPU, it isn't even dual-core - modern Minecraft really needs a quad-core or better CPU to perform well, and even older versions, before 1.8, greatly benefit from at least a dual-core CPU, especially in singleplayer (older versions of Optifine, like 1.6.4, included settings to help improve performance on single-core CPUs but they are no longer present in newer versions since practically everybody has a multicore CPU now; even my old computer, which was older than yours, had a dual-core CPU):
Currently it works best with multi-core systems, quad-core is optimal, dual-core suffers a bit and single-core CPUs are practically doomed with vanilla. Lag spikes are present with all types of CPU.
You really shouldn't be playing on any version newer than 1.6.4 with those specs - the game has gotten vastly more resource-intensive over the years, much more so than new content can explain, which is a prime example of "Wirth's law" (among other names; basically, all state that software gets slower over time, often exceeding hardware performance gains).