Computer system hardware includes the CPU and its associated input and output devices. Input and output devices, separate from the CPU itself, are called peripheral equipment. The CPU communicates with each peripheral device through input and output channels. To operate an electronic-imaging workstation, you must have a general understanding of CPU primary and secondary storage, peripheral devices, input and output channels, and modems.

CPU PRIMARY AND SECONDARY STORAGE

The CPU contains circuits that control and execute instructions by using some type of MEMORY. Memory is referred to by size, such as 16K, 32K, 64K, and so on. The "K" represents the value of 1,000. Therefore 16,000 is 16K.

Semiconductor memory consists of hundreds of thousands of tiny electronic circuits etched on a silicon chip. Each of these electronic circuits is called a BIT CELL and can be in either an OFF or ON state to represent a 0 or 1 bit. This state depends on whether or not current is flowing in that cell. Another name used for semiconductor memory chips is integrated circuits (ICs). Developments in technology have led to large-scale integration (LSI) that allows more and more circuits to be squeezed onto the same silicon chip.

Some of the advantages of semiconductor storage are fast internal processing speeds, high reliability, low power consumption, high density (many circuits), and low cost. However, there is a drawback to this type of storage. It may be VOLATILE, which means it requires a constant power source. When the power for your system fails and you have no backup power supply, all of the stored data is lost.

Primary Storage

Two classifications of primary storage with which you should become familiar are read-only memory (ROM) and random-access memory (RAM).

READ-ONLY MEMORY (ROM).-In computers, it is useful to have instructions that are used often, permanently stored inside the computer. ROM enables us to do this without loosing the programs and data when the computer is powered down. Only the computer manufacturer can provide these programs in ROM; once done, you cannot change it. Consequently, you cannot put any of your own data or programs in ROM. Many complex functions, such as translators for high-level languages, and operating systems are placed in ROM memory.

Since these instructions are hardwired, they can be performed quickly and accurately. Another advantage of ROM is that your imaging facility can order programs tailored for its specific needs and have them installed permanently in ROM. Such programs are called microprograms or firmware.

RANDOM-ACCESS MEMORY (RAM).-RAM is another type of memory found inside computers. It may be compared to a chalkboard on which you can scribble down notes, read them, and erase them when finished. In the computer, RAM is the working memory. Data can be read (retrieved) or written (stored) in RAM by providing the computer with an address location where the data is stored or where you want it to be stored. When the data is no longer requited, you may simply write over it. Thus you can use the storage location again for something else.

Secondary Storage

Secondary storage, or auxiliary storage, is memory external to the main body of the computer (CPU) where programs and data can be stored for future use. When the computer is ready to use these programs, the data is read into primary storage. Secondary storage media extends the storage capabilities of the computer system. Secondary storage is required for two reasons. First, the working memory of the CPU is limited in size and cannot always hold the amount of data required. Second, data and programs in secondary programs do not disappear when the power is turned off. Secondary storage is nonvolatile memory. This information is lost only when you erase it. Magnetic disks are the most common type of secondary storage. They may be either floppy disks or hard disks (hard drives).