“Jukebox” in the context of the Resource Manager means a device that stores a large number of optical disks (compact disks (CDs) or digital versatile disks (DVDs) in something like a rack and inserts a particular disk into a built-in drive upon request. Thus, the term “jukebox” is quite appropriate because it works exactly like its namesake you probably know from places like diners, bars and restaurants. The only difference here is that you don’t have to insert a nickel into the Resource Manager. What is important is that a jukebox usually contains dozens or hundreds of disks in special racks, but it only has a few disk drives at its disposal, some jukeboxes even have only one. This means that only a few or even just one disk can be read at the same time. The jukebox acts like a robot-DJ in that it has to remove a disk from the drive in order to put another disk in. Figure 3 illustrates this concept: A jukebox with its sets of disks, it’s drive(s) and a mechanism for moving disks between drives and disk containers. The Matrixware Resource Manager lets you remotely control an arbitrary number of such robots.

Figure 3: The jukebox as a disk robot
The containers with disks are called magazines, each space for one disk is called a slot. A slot in a magazine is just a place that can hold exactly one disk. It can be empty. A jukebox might contain multiple magazines. Both slots and magazines are enumerated, so that you precisely address which slot in which magazine you mean want to work with. Figure 4 shows a two photographs of an open jukebox, magazines and slots.

Figure 4: A photograph of an open jukebox and its components
The Matrixware Resource Manager can control a large number and large variety of jukeboxes. Those jukeboxes are connected to the Resource Manager and its user in a jukebox network. Figure 5 illustrates the concept of such a jukebox network — the Resource Manager server, running the Resource Manager service, acts as a middleman between the users and the jukeboxes in the jukebox network.

As you might guess, retrieving data from a disk in the jukebox might be slow if the disk has to be moved into the drive first. What’s more, optical disks cannot be read as swiftly as harddisks. On the other hand CDs and DVDs have the advantage of being reliable, cheap and easy to make by the thousands. They can be sent in the mail and filed away in drawers and boxes. So if you want to access particular CD- or DVD data frequently, it is convenient to store them on a harddisk. The Resource Manager is able to copy entire disks into a so-called “virtual” magazine. These virtual magazines contain “virtual” disks — copies of actual disks the Resource Manager has created and stored on its (large) harddisk, more precisely, in a shared Microsoft Windows-folder. This way the Resource Manager server itself becomes a very large and very fast jukebox. The difference is that the “disks” reside on the Resource Manager server’s harddisk. Figure 5 illustrates this concept.

Figure 5: Physical disks in physical magazines in jukeboxes; virtual disks in virtual magazines on the harddrive

In addition to copying disks to shared folders for faster access, the Resource Manager supports copying small disks to larger disks. You can save slots in your jukebox by copying 6 CDs to a single DVD, for example.

All these facilities for managing disks in multiple ways and the resulting plurality of existence of disk data make the usual terms like “disk” and “disk data” problematic because their meaning is not specific enough in the context of the Resource Manager. This is why we will use more precise terms for the rest of this document:

• ISO image. An ISO image is a file that contains all the bits of an entire disk (CD or DVD) as a single file. It is called an ISO image because it is encoded in compliance with the ISO 9660 standard. You can think of an ISO image as a “pickled” disk: not only the actual information on what is stored in the ISO image, but also how. This makes it possible to make an identical copy of the original disk from an ISO image. This is very practical for storing “disembodied” disk data on a hard disk or send it over a network without giving up the option of re-creating an exact copy of the original disk. The Resource Manager makes good use of ISO images. Instead of “virtual disk”, we will use the term “ISO image” from now on.
• Volume. A volume is a physical disk or an ISO image, so it is a generic term for anything that can be treated like disk data, be it an actual disk or a mere ISO image. A volume is atomic in the sense that it cannot be divided in a way that makes sense for the Resource Manager. In other words, the Resource Manager cannot look into a volume, it can only operate on volumes on the whole. This observation is in contrast to a medium — see the next entry.
• Medium. A medium is physical disk, but since it might contain more than one ISO image, it is a special type of volume. A medium is typically a DVD containing multiple CDs as ISO images.
• Virtual Magazine. Like a medium, a virtual magazine is a container for more than one volume. The difference from a medium is that a medium is an optical disk with limited capacity, but a virtual magazine is a shared folder somewhere in the jukebox network and might contain an arbitrary number of volumes (ISO images).

As you can see, the jukebox network is highly hierarchical: The network contains jukeboxes, the jukeboxes contain magazines and drives, the magazines contain slots, each slot can contain a volume. Virtual magazines and media contain ISO images. Figure 6 illustrates this concept of hierarchical containment.

Figure 6: The jukebox network

An important feature of every volume is its label. This is something like its name and is used to identify a particular volume, thus it is embedded in the volume’s bits. Technically, the label is not a filename and not necessarily identical to an ISO image’s filename. The Resource Manager will always try (and succeed) in making the filename identical to the label of the ISO image, but this is a deliberate convention. Identical copies of volumes have identical labels. This means that if you and your neighbour get the same CD-ROM catalogue from ACME Fine Porcelaine in the mail, both disks, and the disks of all customers receiving their copy, for that matter, have the same label. In other words, the label only identifies an issue of volume, not a particular copy. An important task for the Matrixware Resource Manager is to collect the labels of all disks in a jukebox or magazine in order to create a catalogue of disks. This operation is called indexing.

Note: The term “indexing” might be misleading because in computing it has several other meanings, one of those is: To survey a large data repository for fast retrieval later on. This is not the responsibility of the task manager.

Brief term summary

• jukebox — a device for managing large sets of optical disks and providing their data upon request
• magazine — a rack for storing optical disks inside a jukebox
• slot — a place for one disk in a magazine
• virtual disk — Introductory term for a copy of an actual optical disk in a shared folder. The more technical term is “ISO image”.
• virtual magazine — a collection of ISO images in a shared folder.
• Resource Manager server — the computer running the Resource Manager service.
• Resource Manager service — the software interacting with both the user and the jukeboxes, thus enabling the user to control the jukeboxes
• jukebox network — the setup connecting the Resource Manager server, the jukeboxes and the users’ computers with each other and the virtual magazines.
• label A snippet of data embedded in a volume (ISO image or physical disk) naming that volume.
• indexing — Reading all labels from the volumes in the jukebox network and creating a catalogue of these volumes.