64-BIT COMPUTING

Dr. Abdel-Rahman Al-Qawasmi

What Is 64-Bit Computing?

• The labels 64-bit, 32-bit, and so on designate the number of bits that each of the processor's general-purpose registers (GPRs) can hold.

32-bit versus 64-bit programming models

Registers Types

The two types of data that can be processed are integer data and address data., and both integer and address calculations are done by the arithmetic logic unit (ALU).Many modern processors support two additional data types: floating-point data and vector data. Each of these two data types has its own set of registers and its own execution unit(s). The following table compares all four data types in 32-bit and 64-bit processors:

Current 64-Bit Applications

• Dynamic Range:• The base-2, or binary, number system that computers

use has only two symbols with which to represent integers: 0 and 1.

• In moving from a 32-bit GPR to a 64-bit GPR, the range of integers that a processor can recognize and perform arithmetic calculations on goes from 2^32 = 4.3e9 to 2^64 = 1.8e19. The dynamic range, then, increases by a

• factor of 4.3 billion. Thus a 64-bit integer can represent a much larger range of numbers than a 32-bit integer.

Current 64-Bit Applications

• Programmers who run into integer overflow or underflow problems on a 32-bit platform have the option of using a 64-bit integer construct provided by a high-level language like C.

• In addition to scientific computing and simulations, there is another application domain for which 64-bit integers can offer real benefits: cryptography.

Current 64-Bit Applications• Programmers who run into integer overflow or

underflow problems on a 32-bit platform have the option of using a 64-bit integer construct provided by a high-level language like C.

• In addition to scientific computing and simulations, there is another application domain for which 64-bit integers can offer real benefits: cryptography.

• Larger GPRs don’t just make for larger integers, but they make for larger addresses, as well. In fact, larger addresses are the primary advantage that 64-bit computers have over their 32-bit counterparts.

Virtual Address Space vs. Physical Address Space

• Three different types of storage— the caches, the RAM, and the hard disk

• A range of addresses is called an address space, and in a modern 32-bit desktop computer system, the processor and operating system work together to provide each running program with the illusion that it has access to a flat address space of up to 4GB in size. (2^32 = 4.3 billion number? Those 4.3 billion bytes are 4GB, which is the number of bytes that a 32-bit computer can address.)

The Benefits of a 64-Bit Address• The specifics of microprocessor implementation dictate

that there’s a big difference between the amount of address space that a 64-bit address value could theoretically yield and the actual sizes of the virtual and physical address spaces that a given 64-bit architecture supports. In the case of x86-64, the actual size of the Hammer line’s virtual addresses is 48 bits, which makes for about 282 terabytes of virtual address space. x86-64’s physical address space is 40 bits wide, which means that an x86-64 system can support about one terabyte of physical memory (RAM).

Drawback of a 64-Bit Address

• There is one drawback to the increase in memory space that 64-bit addressing affords. Because memory address values are now twice as large, they take up twice as much cache space.

References

• INSIDE THE MACHINE• Jon Stokes 2007.