Hardware and Software Concepts:Firmware.

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Firmware

In addition to hardware and software, most computers contain firmware, executable instructions stored in persistent, often read-only, memory attached to a device. Firmware is programmed with microprogramming, which is a layer of programming below a computer’s machine language.

Microcode (i.e., microprogram instructions) typically includes simple, fundamental instructions necessary to implement all machine-language operations.62 For example,a typical machine instruction might specify that the hardware perform an addition operation. The microcode for this instruction specifies the actual primitive operations that hardware must perform, such as incrementing the pointer that references to the current machine instruction, adding each bit of the numbers, storing the result in a new register and fetching the next instruction.63, 64

Professor Maurice Wilkes, the creator of the early EDSAC computer, first introduced the concepts of microprogramming in 1951.65 However, not until the IBM System/360 appeared in 1964 was microcode used on a wide scale. Machine instruction sets implemented in microcode reached a peak with the VAX operating system, but have declined in recent years, because the execution of microcode instructions limits a processor’s maximum speed. Thus, operations formerly per- formed by microcode instructions are now performed by processor hardware.66 Today, many hardware devices, including hard drives and peripheral devices, con- tain miniature processors. The instructions for these processors are often implemented using microcode.67

Self Review

1. (T/F) There are no instructions smaller than machine-language instructions.

2. Describe the role of firmware in a computer system.

Ans: 1) False. Microcode specifies a layer of programming below a processor’s machine language. 2) Firmware specifies simple, fundamental instructions necessary to implement machine-language instructions.

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