What are the disadvantages of a 64-bit processor versus a 32-bit processor?

Answer 1

There aren't any real disadvantages to 64-bit processors. When running a 64-bit operating system, running a 16-bit application requires a context switch from 64-bit to 32-bit, from 32-bit down to 16-bit, and back to 32-bit and 64-bit. This creates a large performance penalty so in practice most 64-bit operating systems will not allow you to run 16-bit applications. This is unlikely to be a problem for most users, though.

There is one significant disadvantage of 64-bit processors when compared to 32-bit processors: minimum operation size for calculations. A 64-bit processor must do all integer calculations using a 64-bit wide register (that is, all integers must be represented as 64 bits in size). A 32-bit processor does all integer calculations in 32-bit sizes. While performing the actual calculation (e.g. adding two numbers) is neither faster nor slower under 64 vs 32 bit systems, the requirement to pull full 64-bit chunks from memory to do any calculation results in more memory "pressure" than a 32-bit processor.

The result of this is that for a system which does mostly smaller integer calculations (i.e integers which are 231 or small in size), a 32-bit system will have about HALF the memory bandwidth requirement of a 64-bit system. A memory latency is the the dominating factor in modern CPU performance (i.e. the time to get data from memory is far greater than the time to perform a calculation on that data), a 32-bit processor will perform noticeably faster doing such smaller calculations than a 64-bit processor.

A related disadvantage of a 64-bit CPU vs a 32-bit CPU is that the larger operational unit (word) size means that all pathways, registers, and memory units attached to a 64-bit CPU have to be about double the size as required in a 32-bit CPU. This results in about a 40% larger number of transistors required to implement a (roughly) equivalent 64-bit processor vs a 32-bit processor. This does not translate into a 40% higher cost, but does significantly increase production costs; it also significantly increases the thermal profile of the processor (i.e the larger number of transistors requires more power and produces more heat).

Answer 2

You have a low maximum RAM capacity and you can't run x64 programs on it.