Host servers

      Servers are computers which store and process digital objects as well as facilitate the communication between the server and the end-user. Server configurations can range from a single PC-based computer, to clusters of networked workstations, to multiple-processor mainframe systems. The base computations within a computer are accomplished within the central processor(s) of the server. Processors are rated according to the clock speed (i.e. Megahertz or MHz) at which they can manipulate data. The requirements for servers processing plain text are relatively low. However, to process and serve audio and video formatted digital objects may require fast, dedicated multimedia servers.

      The capacity to process data is determined by the amount of primary or main memory called RAM (random access memory) available to the processor to complete the base computations. Memory is measured in bytes – typically one byte is equivalent to one typewriter keystroke. In recent years the engineering of server hardware has advanced the standard configuration of RAM from megabytes (million bytes) to gigabytes or one billion bytes of RAM capacity.

      Auxiliary or secondary memory is secure disk storage within the server. Unlike RAM where the total memory capacity is accessible to the processor at the same time, disk memory must be accessed through a movable magnetic head device. Digital collections are commonly stored within the secondary or disk storage devices and then called into RAM for processing. RAID arrays (Redundant Array of Independent Disks) provide for uninterrupted operation and rapid restoration in the event of disk failure.

      The third form of storage is the remote or offline storage such as tape, Zip disk, CD-ROM or DVD. Historical data files or backup files are captured on these remote storage devices.  Noerr (2000, p. 58) provides examples of storage requirements for a small 100,000 text document collection, audio and video collections.

      A network card installed in the server is required to connect to the global or local network. In some specialized applications where communication speed is critical, dedicated network servers are recommended.

      Dramatic increases in the implementation of e-business applications have contributed to the technological advances that directly benefit the infrastructure also needed to support digital libraries. Overall hardware costs continue to decline, however, demands for computing capacity continue to increase whether for processor speed, memory or network connectivity. In planning for the implementation of a digital library, expandability, flexibility and redundancy are key requirements of a robust and secure server platform. No matter how carefully planned at the beginning, demands for increased processor speed and capacity for RAM and storage upgrades are inevitable.

      Any discussion of hardware requirements for a production server must include security and backup systems. Ideally the server should be placed in a secure room with supplemental cooling. Systematic procedures should be outlined and followed to insure that regular backups of data are performed (daily, weekly and monthly). Those backup tapes or disks should be stored offsite in the event of an environmental disaster effecting the physical location of the server. Hardware can be replaced, however, the investment in data creation and maintenance can span years and in some cases could never be restored or replaced if no backup copies exist. An uninterruptaple power supply (UPS) provides consistent electrical current to the server and in the event of power loss will initiate a controlled shutdown which will protect data and hardware.