32-bit processing
Postcard =
24 in.2 (155 cm2)
64-bit processing
Manhattan =
22 mi.2 (57 km2)
4.3 billion times bigger
To grasp the exponential leap from 32-bit to 64-bit processing, imagine equating the range of numbers a processor can express with a two-dimensional area. A 32-bit processor can express a range of integers equal to the size of a postcard, while a 64-bit processor can express a range of integers larger than the island of Manhattan.
The PowerPC G5 marks the arrival of 64-bit performance to the personal computer market. With 64-bit-wide data paths and registers, this groundbreaking new processor can address vast amounts of main memory and handle multiple large integer and floating-point math calculations in a single clock cycle.
An Exponential Leap in Computing Power
The label “32-bit” or “64-bit” characterizes the width of a microprocessor’s data stream, which is a function of the sizes of its registers and the internal data paths that feed the registers. A 64-bit processor moves data and instructions along 64-bit-wide data paths— compared with the 32-bit-wide paths on 32-bit processors, such as the Pentium 4. In addition, 64-bit processors have wide registers that can store 64-bit numbers as well
as 32-bit numbers.
The leap from 32-bit to 64-bit processing represents an exponential advance in com- puting power. With 32-bit registers, a processor has a dynamic range of 232, or 4.3 billion—which means it can express integers from 0 to 4.3 billion. With 64-bit registers, the dynamic range catapults to 264, or 18 billion billion—4.3 billion times larger than the range of a 32-bit processor.
Memory Addressing up to 18 Exabytes
The move to 64-bit processing results in a similarly dramatic leap in the amount of memory supported. A memory address is a special kind of integer, and each address points to one byte in memory. Since memory addresses are computed in 64-bit registers capable of expressing 18 billion billion integers, the PowerPC G5 can theoretically address 18 exabytes (18 billion billion bytes) of virtual memory.
In practice, memory addressing is defined by the physical address space of the processor. The PowerPC G5, with 42 bits of physical address space, supports a colossal 242 bytes, or 4 terabytes, of system memory. Although it’s not currently feasible to purchase 4 tera- bytes of RAM, very large quantities of memory enable a desktop system to contain a gigantic 3D model, a complex scientific simulation, or a sequence of HD video entirely in RAM—drastically reducing the time to access, modify, and render the data.
