The Move to 64-Bit Computing

8-bit, 16-bit, 32-bit and now 64-bit CPUs. This count seems to be growing in multiples of eight. But what does this bit numbering stand for? This numbering specifies the number of bits the CPU is able to process at one time, that is, in one clock cycle. Intel’s first microprocessor, the 4004, was a 4-bit CPU, after that the counting started. Intel 8085 was an 8-bit CPU, 8086 was a 16-bit CPU, and 80386 marked the beginning of 32-bit microprocessors from Intel. After this, Intel’s Pentium, Pentium pro, Pentium II, Pentium III, Pentium IV, Xeon, Celeron, AMD’s K6, Athlon, Duron all have been 32-bit microprocessors. All said and done, the world is seeing a shift from these 32-bit CPUs to 64-bit CPUs, with the leading chip manufacturers like Intel and AMD offering new 64-bit chips.

But the big question is whether we need these 64-bit CPUs or are the present day 32-bit processors sufficient for meeting our requirements. Also, we cannot say for sure that 64-bit chips will run applications twice as fast as 32-bit chips. The main benefit of 64-bit computing isn’t that it helps in running existing applications faster; it’s that it allows totally different types of applications.

The 8085 with its 16 bits was able to address only 1MB of memory, the 386 increased this limit to 4 GB and beginning with the Pentium the processor was able to address 64 GB of RAM. Thinking this is already more than required? Think again. For large enterprise servers and scientific supercomputers, 64 GB of RAM is a small thing. So, here is where the advantages of 64-bit computing come into the picture. With 64-bit addressing, the processor can access, theoretically, 17 billion gigabytes, that is 17 million terabytes or 16 exabytes. Now, this amount of memory is large for any data-warehouse, enterprise server or a research supercomputer. However, to access these large amounts of memory, support from the OS is also required.

But, is 64-bit computing a new thing or have other chip manufacturers been providing their 64-bit CPUs for some time? Let’s look at various 64-bit processors available in the market and their application areas.

Intel’s Itanium



Intel, along with HP, has worked on an entirely different architecture called the IA-64 for its Itanium line of 64-bit microprocessor. This is not an x86 (or IA-32, as Intel calls it) chip, but a clean new processor. It is still able to run older x86 32-bit programs, but at a slower speed than the current Pentium processors. So, it is not a good option to run 32-bit programs on the new chip. The new architecture is called the EPIC or Explicitly Parallel Instruction Computing. It is available in speeds of 733 and 800 MHz and can scale up to 512 processors. It also features L3 cache of 2 MB or 4 MB for performance enhancement. The successor to the Itanium, called Itanium 2, is also available. It was code-named McKinley.

The processor has clock speeds of I GHz and 900 MHz and L3 cache of 3 MB or 1.5 MB. The front side bus is 400 MHz, 128-bit with a whopping 6.4 GB/s of memory bandwidth. Itanium has got support from major software vendors like Microsoft, which is offering 64-bit versions of its .Net Server 2003 with support for 512 GB of memory and also of the desktop OS, Win XP, with initial support for 16 GB RAM. HP provides its HP-UX for Itanium and major Linux vendors have also released Itanium-compatible versions for Linux. The Itanium targets application areas like large databases, security transactions, business intelligence and mechanical computer-aided engineering analysis.

AMD’s Hammer



Although Intel has left the x86 architecture, which it originally developed for the 64-bit CPUs, AMD has extended the architecture to 64-bit (code named Hammer). AMD offers two lines of 64-bit chips, one for the server market and the other for the home and desktop market, maybe the next generation

Athlon.

The server processor is offered as Opteron with both 32-bit and 64-bit application support. As the new chips originally support the x86 architecture, they are able to run 32-bit code faster than the Athlon XP as well as 64-bit programs. This way performance is not compromised for either mode. Though the chip is based on x86 architecture it still needs software support, and this is relatively easy to do with this chip than with the Itanium as the x86-64 architecture simply extends the x86 instruction set to 64 bit instructions.

As AMD also offers desktop-based 64 bit chips, it is seen that new gaming and multimedia applications will take advantage of the new CPUs to provide high-performance experience to the home users. This way home users stand to benefit directly from 64-bit computing.

These were the latest chips from two of the world’s leading chip manufacturers, but 64-bit CPUs have been here for quite some time with processors like the ALPHA, HP-PA RISC, IBM Power4 and Sun UltraSparc. All these have been running proprietary versions of Unix like IBM’s AIX, Sun’s Solaris, etc.

Sun’s UltraSparc



Sun’s UltraSparc III is a RISC (reduced instruction set computing) processor. The current processor runs at 1.05 GHz and provides world-class performance on Sun workstations and servers with Solaris OS. The x86 processors are all CISC (complex instruction set computing) processors, but with the Pentium and further processors they have been all become RISC machines internally. All CISC instructions are decoded to RISC instructions before entering the pipeline of all Pentium processors. This shows the performance superiority of RISC-based machines. The Sparc is made with 0.15 micron technology and up to 8 MB of external L2 cache and can access up to 16 GB of memory per processor. These processors are mainly used in high-end servers, like the Sun-Fire 3800 which can support up to 8 processors and 64 GB of RAM or the Sun Fire datacenter server supporting over 100 processors and 512 GB of RAM. All these run Sun’s version of Unix called



Solaris.

Alpha



Alpha processors were a replacement for MIPS processors, which were replacements for VAX processors. These are again RISC processors. Alpha processors were the first to reach the 1 GHz speed barrier. Compaq offers high end alpha-based servers for mainframe server and entry-level server market with support for up to 32 processors and 512 MB of memory and 16 MB cache per processor. These systems run OpenVMS, Linux and Tru 64 Unix.

Power 4



This processor from IBM is a heavy-weight champion. It includes a module having eight 64-bit processors on one unit. There are two processor cores on a die and four die on a module making a total of eight. The power requirements of the processor are huge consuming up to 500 watts of power. It is fabricated using 0.18 micron technology and contains over 600 million transistors. The processors come with the IBM e-server pseries of servers and run IBM’s AIX version of UNIX.

HP’s PA-RISC Processors



These processors come with HP’s range of servers and run HP-UX OS. The processors come at a clock speed of 1 GHz.



These were the 64-bit processors available for use in high-end systems delivering unheard of performance. While the Alpha, Sparc, Power, PA-RISC processors run proprietary OSs, the Itanium and Opteron processors are meant for general use and they are also attracting major software vendors to develop solution based on these processors. This shows in the fact that Unix, Linux and Windows-based OSs are available for the Itanium chip and Microsoft may be supporting the AMD 64-bit chips also, whereas other processors still run software developed by the same company.

All these processors have different application areas. Sparc mostly runs on Sun workstation and servers and is seen to be doing that only.

IBM’s power is used in supercomputing, number-crunching requirements of researchers and scientists.

PA-RISC processors are also supported by HP’s range of servers and OS only.

This said, now AMD and Intel’s 64-bit offerings are left for the mainstream enterprise market. Software support and user choice will decide which of the two processor will be successful as this time both processors seem to be going in different directions with different architectures. While Intel is going with a new and, proclaimed, better IA-64 architecture, AMD is sticking with x86.

In the end, it remains to be seen when these 64-bit processors will enter the mainstream computing arena, where presently 32-bit CPUs rule the roost.

Anoop Mangla