Drive space and efficiency
Addressing applies to disks just as it does for memory. This requires a change to a different file system, but a file system with more bits can use smaller data clusters, access larger disks, and handle more files. In the short term, efficient use of the current disk space would be the goal. As you'll recall, Windows 95 changed the disk system from the 16-bit FAT16 file system that was limited to about 2 GB per partition to a 32-bit file system with a theoretical limit of 8 TBs per partition, although that requires using 32-KB data clusters. Since a cluster is the smallest increment on a disk, any file smaller than 32 KB leaves wasted space, and any file that does not evenly fit into 32-KB increments leaves wasted space. Smaller clusters mean more files on the same disk. The inverse is using larger disks with the same cluster sizes. The number of files is also an issue with large volumes because a 32-bit file system is limited to about 4.3 billion files. Again, it seems like a lot, but when a desktop workstation may have a RAID array of nearly half a TB, how long will that last for the servers or something like a storage area network? 64 bit: "Husky-sized" data
Bigger is not always better. Since the system uses 64-bit values instead of 32-bit values, memory needs to increase. Simply storing the value 0 requires a 64-bit block (8 bytes) in RAM. The exact amount of memory increase will vary with the application because memory needs don't directly double since executable binary data will be managed differently, but expect at least a 10 percent increase in used memory space. On a less visible front, the processor's cache memory will be hit quite hard. Like the active memory, the executable data will not suffer from the doubling, but the cache doesn't store as much executable data. The use of 64-bit registers and 64-bit values in the cache will create a notable dent, probably reducing the effective space in the cache by 30 percent. This will increase the cost of 64-bit processors in two ways. The first is that cache memory is far more expensive because the processor cache runs at processor speeds rated in GHz rather than the more sedate MHz of RAM. The second is that memory requires transistors, and the more transistors you have on a chip, the greater the odds that some of them will be bad, increasing the percentage of dud processors being churned out. Both combine to increase the cost of a 64-bit processor. Is 64 bit for your organisation?
Naturally, the only one who can answer the 64-bit question is the informed CIO. For now, it can be ruled out on the desktop, but the data center and high-end workstations are likely candidates. Also, Web servers full of static content, VPN gateways, and database servers are all good choices. The truly hard choice is how to make the leap. If you need Windows on your 64-bit processor, you'll first have to wait until the fall, and then you can use either the Intel Itanium or possibly the AMD Opteron. If you don't absolutely require Windows, the choice is much easier. There are several 64-bit processors with years of testing under a variety of Unix and VMS environments that have a sizable arsenal of proven applications at roughly the same price. No one said being an informed CIO was easy. For a weekly round-up of the enterprise IT news, sign up for the
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