Main memory and DASD

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Main memory and DASD

Postby silambarasan » Sun Jun 26, 2011 2:23 pm

we have 16EB main memory then why we need DASD ?
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Re: Main memory and DASD

Postby BillyBoyo » Sun Jun 26, 2011 2:49 pm

1) It is unlikely that you have all that memory.
2) What if someone powers down.
3) Why hold long-term storage in short-term storage area.
4) etc.
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Re: Main memory and DASD

Postby NicC » Sun Jun 26, 2011 10:46 pm

Do you know what 'DASD' is?
The problem I have is that people can explain things quickly but I can only comprehend slowly.
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Re: Main memory and DASD

Postby steve-myers » Mon Jun 27, 2011 9:30 am

silambarasan wrote:we have 16EB main memory then why we need DASD ?
You may have that much virtual storage, but is unlikely you have more than a few dozen gigabytes real storage.

The problem with most real storage is its contents won't survive losing power. In fact most real storage is DRAM, which only retains data for a few seconds. There is a constant background process running all the time to read DRAM and immediately restore what was just read. That's what DASD is for: to retain data for the long term.

There has been some talk on the trade press about holding data in storage rather than on disk, and this reduces the need for data base management systems. Nonsense. The database management works somewhat differently, but it's still there.
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