64 bit - What are the lower level advantages and disadvantages of 64-bit/32-bit?

Question

I'm sure we've all heard the terms 64bit and 32bit thrown around, but what do they actually mean?

I'm pretty sure they have to do with the size of a memory address. On a 64bit machine, a reference to an object is 64 bits. But I want to dig a little deeper....

1. One often hears the phrase "64bit machine." What part of the computer is actually geared toward the number of bits? Processor? Operating System?

2. What is the advantage of having larger memory addresses?

I could add more questions, but I think brief is better.

Thanks guys :D

Answer 1

64 bit refers to the width of registers, memory addressing space, etc. One benefit is the ability to address more than 4GB of memory.

Wikipedia has an article on 64-bit computing with more details.

Edit: The advantages to more memory are that the operating system and programs have more virtual addressing space--16 exabytes (17.2 billion GB)--and, more importantly, that more physical memory can be added to a system and addressed, causing less swapping of virtual memory to and from disk.

The advantage to wider registers and data buses are that it is easier and faster to move the same amount of data around. An operation that required two or more registers can now be done with one.

So, performance is typically increased when software is recompiled for 64 bits.

A disadvantage is that wider data can mean more space taken by the same data. For instance storing the number 300 requires nine bits. If it's stored in a 32 bit integer, 23 bits are wasted. In 64 bit, that wastage becomes 55 bits. So, without retooling, a simple recompile to 64 bit can yield faster, but slightly more bloated software.

Edit: Also there are 64-bit technology pages here:

• Intel? 64 Architecture
• AMD64 Solutions
• IBM: From the stacks: Making the transition to 64 bits
• IBM: Porting Linux applications to 64-bit systems
• IBM: 64-Bit Computing Decision-Maker’s Guide
• CodingHorror: Is it time for 64 bit on the desktop?
• ClassicArs: An Introduction to 64-bit Computing and x86-64