RAM is 100 Thousand Times Faster than Disk for Database Access

By Steve Gilheany

If you have a problem with slow database (or GIS) access, placing the entire database (or GIS) in RAM can instantly provide a factor-of-100-thousand increase in access speed with no other programming or data structure changes required.The access time to data in RAM is on the order of 50 nanoseconds (5 x 10 **-8 seconds).The access time to data on disk is on the order of 5 milliseconds (5 x 10 **-3 seconds).The difference is 10**5 or a factor of 100 thousand increase in speed.This is because GIS processing is much more disk access intensive than computation intensive.This has always been the case, but is even more so today with 3 GigaHertz processors making quick work of GIS computations.

The switch to RAM-based GIS systems will happen soon, because RAM is approaching USD $500 per GigaByte and the cost of the RAM required to store a 30 GigaByte GIS system is approaching USD $15 thousand.For a 5 Gigabyte GIS, the cost would be USD $2,500.Virtual memory provides an easy method for making data RAM-resident with a minimum of changes in design.Larger database vendors can facilitate the conversion to RAM resident databases and GIS systems.In the same way that software is loaded before an application starts, soon the data for an application will load before the application starts.Similarly, fully RAM-resident operating systems will provide a similar increase in speed.

Servers using 64-bit addressing can potentially address up to 16 ExaBytes (2**64 bytes) (about 16 quintillion or 16 billion billion bytes), and in all cases can access at least one terabyte (2**40 bytes) (about 1 trillion bytes).Servers using 32-bit addressing can address 4 gigabytes (2**32 bytes) (about 4 billion bytes), often with restrictions on addressing over 2 gigabytes.The continued shift to 64-bit computing will facilitate the factor-of-100-thousand increase in GIS speed, which is provided by a shift to RAM for all GIS data access.See [http://www.ArchiveBuilders.com/whitepapers/22045p.pdf] and [http://www.ArchiveBuilders.com/whitepapers/22046p.pdf]

With Samsung's introduction of the 4 GigaByte (DDR) Double Data Rate (DIMM) Dual In-line Memory Module, every PC can have 16 GigaBytes of RAM (with the standard maximum of 4 memory modules installed in the PC) (Some servers can accommodate more than 4 memory modules).[http://www.Samsung.com/press/news_finder_read.cgi?lidx=20030120195842] Now you can have 16 GigaBytes in your PC, but you can only use 4 GigaBytes of it because your obsolete 32-bit operation system can only address 4 GigaBytes.We will be back to the time when you could buy 1 MegaByte of RAM for your PC, but you could only use 640 KiloBytes (10 x (2 ** 16) bytes) of your 1 MegaByte of RAM because of 10 x 16-bit operating system limitations. And, most GIS software is still 32-bit and not yet ready to use 16 GigaBytes of RAM.Only some of the larger database systems are 64-bit and can use 16 GigaBytes (and more) of RAM.The transition from 16-bit to 32-bit computing was painful, but happened so long ago that most newly minted IT (Information Technology) professionals have never heard of it.The transition from 32-bit to 64-bit computing will be similarly challenging, and even fewer people will believe that there will ever be another transition to a larger address space above the 64-bit address space (the ability to address 16 ExaBytes).

At the same time that RAM is getting much less expensive, and the size of RAM in PCs is expanding exponentially, RAID (Redundant Array of Inexpensive Disks) is also dropping rapidly in price and increasing exponentially in size.Vitesse.com says that its recently announced RAID serial ATA controller will allow OEMs to design a 4-TeraByte disk array based on Maxtor Corp.'s new 250-MegaByte Maxtor serial ATA drives that would cost about $6,000, or $1,500 per TeraByte.[http://www.eetimes.com/semi/news/OEG20030121S0031]

Backup using 27 GigaByte per layer blue-light special DVD-R burners is getting closer to a low cost introduction with Sanyo's schedules production of 35-mW blue-violet lasers for blue-light burning.[http://www.eetimes.com/story/OEG20030121S0034] When blue-light DVD media drops to one dollar, a TeraByte can be backed up for $40.

These developments will allow the incorporation of an almost unlimited volume of raster images in GIS systems with no concern for storage costs or Internet transmission speed.All versions of frequently updated digital orthophotos can be kept on line for instant time series analysis of development and ecological change.See [http://www.ArchiveBuilders.com/whitepapers/22056p.pdf] Old maps and infrastructure drawings can be raster scanned at 400 dpi and 8-bits of grayscale.See [http://www.ArchiveBuilders.com/whitepapers/22058p.pdf]

By .(JavaScript must be enabled to view this email address) More whitepapers on GIS and document management, classes, and updates at [http://www.ArchiveBuilders.com]

Published Wednesday, January 29th, 2003

Written by Steve Gilheany

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