In computer architecture, 64-bit integers, memory addresses, or other data units are those that are at most 64 bits (8 octets) wide. Also, 64-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. Similar is the case with 32-bit CPU & ALU will have 32 bits wide registers, address buses or data buses.
Linux Memory Architecture
To execute a process, the Linux kernel allocates a portion of the memory area to the requesting process. The process uses the memory area as workspace and performs the required work. Today we are faced with the choice of 32-bit systems and 64-bit systems. One of the most important differences for enterprise-class clients is the possibility of virtual memory addressing above 4 GB. From a performance point of view, it is interesting to understand how the Linux kernel maps physical memory into virtual memory on both 32-bit and 64-bit systems.
As you can see in Figure 1 there are obvious differences in the way the Linux kernel has to address memory in 32-bit and 64-bit systems. Exploring the physical-to-virtual
mapping in detail is beyond the scope of this article , so I highlight some specifics in the Linux memory architecture.
On 32-bit architectures such as the IA-32, the Linux kernel can directly address only the first gigabyte of physical memory (896 MB when considering the reserved range). Memory above the so-called ZONE_NORMAL must be mapped into the lower 1 GB. This mapping is completely transparent to applications, but allocating a memory page in ZONE_HIGHMEM causes a small performance degradation.
On the other hand, with 64-bit architectures such as x86-64 (also x64), ZONE_NORMAL extends all the way to 64 GB or to 128 GB in the case of IA-64 systems. As you can see, the overhead of mapping memory pages from ZONE_HIGHMEM into ZONE_NORMAL can be eliminated by using a 64-bit architecture.
Advantages of 64-bit over 32-bit
A common misconception is that 64-bit architectures are no better than 32-bit architectures unless the computer has more than 4 GB of main memory. This is not entirely true.
Some operating systems reserve portions of process address space for OS use, effectively reducing the total address space available for mapping memory for user programs. For instance, Windows XP DLLs and other user mode OS components are mapped into each process’s address space, leaving only 2 to 3 GB (depending on the settings) address space available. This restriction is not present in 64-bit operating systems.
Memory-mapped files are becoming more difficult to implement in 32-bit architectures, especially due to the introduction of relatively cheap recordable DVD technology. A 4 GB file is no longer uncommon, and such large files cannot be memory mapped easily to 32-bit architectures.Some programs such as data encryption software can benefit greatly from 64-bit registers (if the software is 64-bit compiled) and effectively execute 3 to 5 times faster on 64-bit than on 32-bit.
Some complex numerical analysis algorithms are limited in their precision by the errors that can creep in because not all floating point numbers can be accurately represented with a small number of bits.
On 32-bit architectures the maximum address space a single process can access is 4 GB. On the other hand, on 64-bit architecture such as x86_64 and ia64, no such restriction exists.
Each single process can benefit from the vast and huge address space.
Disadvantage of 64-bit
The main disadvantage of 64-bit architectures is that relative to 32-bit architectures the same data occupies more space in memory (due to swollen pointers and possibly other types and alignment padding). This increases the memory requirements of a given process and can have implications for efficient processor cache utilization.
How to identify whether CPU is 64 bit or 32 bit ?
Linux users should type the uname command. Depending on the platform, you may see
[root@server1 ~]$ uname -a
Linux 2.6.11-1.27_FC3 #1 Tue May 17 20:24:57 EDT 2005 x86_64 x86_64 x86_64 GNU/Linux
[root@server2 ~]$ uname -a
Linux 2.6.9-5.0.5.EL #1 SMP Fri Apr 8 14:20:58 EDT 2005 ia64 ia64 ia64 GNU/Linux
[root@server3 ~]$ uname -a
Linux 2.6.10-1.771_FC2smp #1 SMP Mon Mar 28 01:10:51 EST 2005 i686 i686 i386 GNU/Linux
In the above listing, ‘server1’ (x86_64 GNU/Linux) and ‘server2’ (ia64 GNU/Linux) are 64-bit compliant. While ‘server3’ (i386 GNU/Linux) is only a 32-bit platform.
Microsoft Windows Server 2003
1.Click Start, click Run, type sysdm.cpl, and then click OK.
2.Click the General tab. The operating system appears as follows:
For a 64-bit version operating system: Microsoft Windows Server 2003 Enterprise x64 Edition appears under System.
For a 32-bit version operating system: Microsoft Windows Server 2003 Enterprise Edition appears under System.
1.Click Start, click Run, type winmsd.exe, and then click OK.
2.In the details pane, locate Processor under Item. Note the value.
If the value that corresponds to Processor starts with x86, the computer is running a 32-bit version of the Windows operating system.
If the value that corresponds to Processor starts with EM64T or ia64, the computer is running a 64-bit version of the Windows operating system.
Linux Performance and Tuning Guidelines (ibm.com/redbooks)