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A front panel was used on early electronic computers to display and allow the alteration of the state of the machine's internal registers and
memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembe ...
. The front panel usually consisted of arrays of indicator lamps, digit and symbol displays,
toggle switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type o ...
es, dials, and push buttons mounted on a sheet metal face plate. In early machines,
CRT CRT or Crt most commonly refers to: * Cathode-ray tube, a display * Critical race theory, an academic framework of analysis CRT may also refer to: Law * Charitable remainder trust, United States * Civil Resolution Tribunal, Canada * Columbia ...
s might also be present (as an oscilloscope, or, for example, to mirror the contents of Williams–Kilburn tube memory). Prior to the development of CRT
system console A computer terminal is an electronic or electromechanical computer hardware, hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. Most early computers only had a front panel to ...
s, many computers such as the
IBM 1620 The IBM 1620 was a model of scientific minicomputer produced by IBM. It was announced on October 21, 1959, and was then marketed as an inexpensive scientific computer. After a total production of about two thousand machines, it was withdrawn on N ...
had console typewriters. Usually the contents of one or more
hardware register In digital electronics, especially computing, hardware registers are circuits typically composed of flip-flops, often with many characteristics similar to memory, such as: * Using an memory or port address to select a particular register in a ma ...
s would be represented by a row of lights, allowing the contents to be read directly when the machine was stopped. The switches allowed direct entry of data and address values into registers or memory.


Details

On some machines, certain lights and switches were reserved for use under program control. These were often referred to as ''sense indicators'', ''sense lights'' and '' sense switches''. For example, the original Fortran compiler for the
IBM 704 The IBM 704 is the model name of a large digital computer, digital mainframe computer introduced by IBM in 1954. Designed by John Backus and Gene Amdahl, it was the first mass-produced computer with hardware for floating-point arithmetic. The I ...
contained specific statements for testing and manipulation of the 704's sense lights and switches. These switches were often used by the program to control optional behavior, for example information might be printed only if a particular sense switch was set. Operating systems made for computers with '' blinkenlights'', for example,
RSTS/E RSTS () is a multi-user time-sharing operating system developed by Digital Equipment Corporation (DEC, now part of Hewlett-Packard) for the PDP-11 series of 16-bit minicomputers. The first version of RSTS (RSTS-11, #Versions, Version 1) was implem ...
and
RSX-11 RSX-11 is a discontinued family of multi-user real-time operating systems for PDP-11 computers created by Digital Equipment Corporation. In widespread use through the late 1970s and early 1980s, RSX-11 was influential in the development of later ...
, would frequently have an idle task blink the panel lights in some recognizable fashion. System programmers often became very familiar with these light patterns and could tell from them how busy the system was and, sometimes, exactly what it was doing at the moment. The Master Control Program for the
Burroughs Corporation The Burroughs Corporation was a major American manufacturer of business equipment. The company was founded in 1886 as the American Arithmometer Company by William Seward Burroughs I, William Seward Burroughs. The company's history paralleled many ...
B6700 mainframe would display a large block-letter "B" when the system was idle. Switches and lights required little additional logic circuitry and usually no software support, important when logic hardware components were costly and software often limited. While other machines of its day had elaborate front panels to control them, the 6600 has only a ''dead start panel''. There is a dual CRT system console, but it is controlled by operating system code on a peripheral processor and neither controls nor displays the hardware directly. Early
microcomputer A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor. The computer also includes memory and input/output (I/O) circuitry together mounted on a printed circuit board (P ...
s such as the 1975
Altair 8800 The Altair 8800 is a microcomputer introduced in 1974 by Micro Instrumentation and Telemetry Systems (MITS) based on the Intel 8080 CPU. It was the first commercially successful personal computer. Interest in the Altair 8800 grew quickly after i ...
also relied on front panels, but since the introduction of the
Apple II Apple II ("apple Roman numerals, two", stylized as Apple ][) is a series of microcomputers manufactured by Apple Computer, Inc. from 1977 to 1993. The Apple II (original), original Apple II model, which gave the series its name, was designed ...
, TRS-80, and Commodore PET during the home computer boom of 1977, the vast majority of microcomputers came with keyboards and connections for TV screens or other monitors.


Common usage

An operator would use the front panel to bootstrap the computer, to
debug In engineering, debugging is the process of finding the root cause, workarounds, and possible fixes for bugs. For software, debugging tactics can involve interactive debugging, control flow analysis, log file analysis, monitoring at the ap ...
running programs, and to find hardware faults.


Storage alteration and display

Many computers had controls, e.g., buttons, dials, keyboards, toggle switches, for entering addresses, controls for displaying the data at an address and controls for altering storage contents. These were typically used for booting and debugging.


Booting

Typically, the operator would have a written procedure containing a short series of bootstrap instructions to be hand-entered using, e.g., dials, keyboard, toggle switches. First, the operator would, e.g., press the address switch and enter the address. For easier entry and readout, on some computers (such as the DEC
PDP-8 The PDP-8 is a family of 12-bit minicomputers that was produced by Digital Equipment Corporation (DEC). It was the first commercially successful minicomputer, with over 50,000 units sold during the model's lifetime. Its basic design follows the pi ...
or MITS
Altair 8800 The Altair 8800 is a microcomputer introduced in 1974 by Micro Instrumentation and Telemetry Systems (MITS) based on the Intel 8080 CPU. It was the first commercially successful personal computer. Interest in the Altair 8800 grew quickly after i ...
) binary digits were grouped into threes or fours on the front panel, with each group of lights or switches representing a single
octal Octal (base 8) is a numeral system with eight as the base. In the decimal system, each place is a power of ten. For example: : \mathbf_ = \mathbf \times 10^1 + \mathbf \times 10^0 In the octal system, each place is a power of eight. For ex ...
(between 0 and 7) or
hexadecimal Hexadecimal (also known as base-16 or simply hex) is a Numeral system#Positional systems in detail, positional numeral system that represents numbers using a radix (base) of sixteen. Unlike the decimal system representing numbers using ten symbo ...
(between 0 and F) digit. Some decimal computers, e.g.,
IBM 1620 The IBM 1620 was a model of scientific minicomputer produced by IBM. It was announced on October 21, 1959, and was then marketed as an inexpensive scientific computer. After a total production of about two thousand machines, it was withdrawn on N ...
, used
binary-coded decimal In computing and electronic systems, binary-coded decimal (BCD) is a class of binary encodings of decimal numbers where each digit is represented by a fixed number of bits, usually four or eight. Sometimes, special bit patterns are used f ...
for memory addresses. Next the operator would enter the value intended for that address. After entering several of these instructions (some computers had a deposit next button, which would deposit subsequent values in subsequent addresses, relieving the operator of needing to enter subsequent addresses), the operator would then set the starting address of the bootstrap program and press the run switch to begin the execution of the program. The bootstrap program usually read a somewhat longer program from punched paper-tape, punched cards, magnetic tape, drum or disk which in turn would load the operating system from disk. Some machines accelerated the bootstrap process by allowing the operator to set the controls to contain one or two
machine language In computer programming, machine code is computer code consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). For conventional binary computers, machine code is the binaryOn nonb ...
instructions and then directly executing those instructions. Other machines allowed I/O devices to be explicitly commanded from the front panel (for example, "Read-In Preset" on the
PDP-10 Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, especi ...
or the accessing of
memory-mapped I/O Memory-mapped I/O (MMIO) and port-mapped I/O (PMIO) are two complementary methods of performing input/output (I/O) between the central processing unit (CPU) and peripheral devices in a computer (often mediating access via chipset). An altern ...
devices on a
PDP-11 The PDP–11 is a series of 16-bit minicomputers originally sold by Digital Equipment Corporation (DEC) from 1970 into the late 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of a ...
). Some machines also contained various bootstrap programs in
ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * ...
and all that was required to ''boot'' the system was to start it executing at the address of the correct ROM program.


Debugging

Front panels were often used to debug programs when operating support was limited and most programs were run in stand-alone mode. Typically a front-panel switch could cause the computer to ''single-step'', that is run a single instruction and stop until the programmer pressed a button to execute the next instruction. An ''address stop'' could be set to stop a running program when it attempted to execute an instruction or access data at a specified address. The contents of registers and memory would be displayed in the front-panel lights. The programmer could read and alter register contents, change program instructions or data in memory or force a branch to another section of code. When multiprogramming became the norm it was no longer acceptable to tie up an entire machine for debugging, except for special situations. Programs called ''
debugger A debugger is a computer program used to test and debug other programs (the "target" programs). Common features of debuggers include the ability to run or halt the target program using breakpoints, step through code line by line, and display ...
s'' were written which provided the programmer with the equivalent of the front-panel functions without requiring the entire machine.


Entertainment

For fun, bored programmers would create programs to display animated light shows. Front panels in the late 1960s and early 1970s were quite brightly colored. In the late 1970s and early 1980s, bootstrap ROMs became common. Since computers could use them to start themselves without operator intervention, most computers were built without a front switch panel. High-powered calculators, such as the
HP 9830 The HP 9800 is a family of what were initially called programmable calculators and later desktop computers that were made by Hewlett-Packard, replacing their first HP 9100 calculator. It is also named "98 line". The 9830 and its successors were ...
based on
ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * ...
, were among the first computers to do away with front panels and operators. Huge banks of "blinkenlights" and "blowenfuzen" were featured on TV and movies as the popular image of the "computer" during the 1950s to 1970. (A Burroughs B205 was used as a Hollywood prop for many of these shows.)


Example

The following procedure would bootstrap a
PDP-8 The PDP-8 is a family of 12-bit minicomputers that was produced by Digital Equipment Corporation (DEC). It was the first commercially successful minicomputer, with over 50,000 units sold during the model's lifetime. Its basic design follows the pi ...
system from an RK05 moving-head magnetic disk: # Ensure that the machine is halted by lowering and raising the Halt switch; the front panel "RUN" light should then be off. # Set the 12 data switches to 0030 (Octal address 30), depress the Load Address ("ADDR LOAD") switch. The address lights will change to "0030". # Set the switches to 6743, raise the Deposit switch. The data lights will show this instruction. # Set the switches to 5031, raise the Deposit switch. The data lights will show this instruction. # Set the switches to 0030 (Octal address 30), depress the Load Address switch. The address lights will change back to "0030". # Depress the Clear switch. # Depress the Continue switch. The "RUN" light will illuminate and the operating system on the disk will be bootstrapped. This process works by depositing a simple, two-instruction program in memory and executing it. The first instruction commands the disk controller to begin reading the disk from the current disk address into the current memory address. The second instruction is a JMP instruction that jumps to itself endlessly. When "Clear" is pressed, the disk controller's current disk address is set to sector 0 and its current memory address is set to memory location 0000. When the read is commanded, the program stored in disk sector 0 overlays the bootstrap program and, once the JMP instruction is overlaid, the disk program takes control of the machine.


Notes


References

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