Chapter III, Desktop Imaging Systems and Issues: Lesson II Storing Image Data http://www.kodak.com/country/US/en/digital/dlc/book3/chapter3/deskImgM2_1.shtml

                             Imaging files place great demand on storage for processing, for transfer to a service bureau or printer, and for backup and archival storage.

                             Efficient processing of images requires enough RAM to hold multiple copies of the image in process. For example, when an image is edited, new changes are stored separately from the previous state of the image. This allows one to undo a change, if necessary.

                             For instance a 2k by 3k resolution color image requires 18 megabytes of storage when opened for editing. When using software such as Photoshop, about 36 megabytes are needed to edit efficiently. Insufficient RAM can lead to severe performance limitations. Virtual memory is often used to compensate for lack of RAM.

                             Virtual memory schemes use part of the hard disk as RAM. This may be done either by the operating system or the application software. Virtual memory is much slower than RAM since the contents of RAM must be swapped to disk to free RAM for working on other parts of the image.

                             The easiest and least expensive way to upgrade a computer's image handling performance is to increase RAM. An adequate amount of RAM reduces the number of times the computer needs to access the hard drive for image data.

                             Images usually require temporary storage during processing. For instance, when compositing several images, you may need quick access to each image component. A dedicated hard drive provides quick access as well as very high transfer rates.

                             A disk array is an alternative which provides drive performance almost as fast as RAM. Two or more fixed drives working in parallel virtually double the speed of individual drives. Because of their cost, disk arrays are typically found on high end systems such as SGI's (Silicon Graphics Workstations and Servers).

                             Another image storage need is for transferring completed image files to a service bureau or to a printer.

                             Removable magnetic media, such as SyQuest and Bernoulli cartridges in a variety of storage capacities, are commonly used for this kind of image file transfer.

                             Advances in the manufacture of SCSI (Small Computer Systems Interface) hard drives have made large-capacity external SCSI drives another affordable image transfer option.

                             Magneto optical drives also provide high capacity/low volume erasable optical storage.

                             An emerging transfer alternative is the PCMCIA hard drive. These small drives currently store more than 100 megabytes, and will soon be in the 1 gigabyte range.

                             The PCMCIA drive is becoming a preferred option for digital cameras because of the ease with which it can transfer image data to a computer for processing.

                             Original and processed images often need to be stored for future use or for archival purposes.

                             File servers equipped with large hard disks provide quick access to shared image files.

                             For longer term storage, data tape provides a low cost, high reliability option. But since tape is a serial medium, data is written and accessed sequentially rather than randomly as with other media. This makes retrieval slow.

                             Writable CD is a long term storage alternative which offers random access as well as high capacity and ease-of-use. Since Writable CD is appendable, additional image files can be added or deleted at different times.

                             Compact disc libraries, or jukeboxes, in combination with Writable and Photo CD, provide handy access to a collection of archived images. This jukebox can store up to 10,000 16base resolution Photo CD images in a fraction of the space required by an equal-capacity file server.