3.3.3 Layout of Major Components

including the CPU, memory, motherboard chip set, IDE, PCI, USB, boot drives, plug-n-play capability, and power control interfaces.
3.6 Secondary Storage
With the exception of the BIOS ROM, all information in memory is lost during power cycling except for that provided by a set of external (to the motherboard) devices that fall under the category of secondary storage. Of these, disk drives, floppy drives, and CD-ROM drives are most frequently found on Beowulf nodes. Disk and floppy drives are spinning magnetic media while CD-ROM drives (which are also a spinning media) use optical storage to hold approximately 650 MBytes of data. The newer DVD technology is likely to replace CD-ROM in the near future. Besides persistence of storage, secondary storage is characterized by very high capacity and low cost per bit. While DRAM may be purchased at about $1/MB, disk storage costs 2 or 3 cents per MByte and the price continues to fall. For the particular case of Beowulf, these three modes of secondary storage play very different roles.
CD-ROMs provide an easy means of installing large software systems but are used for little else. Even for this purpose, only one or two nodes in a system are likely to include a CD ROM drive because installation of software on most of the nodes is performed over the system area network.
Floppy discs are fragile and slow and don't hold very much data (about 1.44 MByte). They would be useless, except that they were the primary means of persistent storage on early PCs, and PC designers have maintained backward compatibility that allows systems to boot from a program located on floppy disk. Occasionally, something goes terribly wrong with a node (either due to human or system error), and it is necessary to restore the system from scratch. A floppy drive and an appropriate "boot floppy" can make this a quick, painless and trouble-free procedure. Although other means of recovery are possible, the small price of about $15 per node for a floppy drive is well worth the investment.
The hard drive serves three primary purposes. It maintains copies of system wide programs and data so that these do not have to be repeatedly acquired over the network. It provides a large buffer space to hold very large application data sets. And it provides storage space for demand paging as part of the virtual memory management system. When the user or system memory demands exceed the available primary memory, page blocks can be automatically migrated to hard disk, making room in memory for other information to be stored.

 



How to Build a Beowulf
How to Build a Beowulf: A Guide to the Implementation and Application of PC Clusters (Scientific and Engineering Computation)
ISBN: 026269218X
EAN: 2147483647
Year: 1999
Pages: 134

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