Front panel

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The front panel is used on the earliest electronic computer to display and allow changes to the internal register status and the machine's internal memory. The front panel usually consists of an array of indicator lights, toggle switches, and push buttons mounted on the metal sheet plate. In the initial machine, CRTs may also be present (as oscilloscopes, or, for example, to reflect the contents of the Williams-Kilburn tube memory). Prior to the development of the CRT system console, many computers like the IBM 1620 had a typewriter console.

Usually the contents of one or more hardware registers will be represented by a row of lights, allowing the content to be read directly when the machine is stopped. Switches allow direct entry of data and address values ​​into registers or memories.

Video Front panel

Detail

On some machines, certain lights and switches are provided for use under the control of the program. This is often referred to as the sensory lamp and the sensory switch . For example, the original Fortran compiler for IBM 704 contains specific statements for the testing and manipulation of lamps and 704 senses switches. These switches are often used by programs to control optional behavior, for example information may be printed only if a certain flavor switch is set.

Operating systems created for computers with blinkenlight , for example, RSTS/E and RSX-11, will often have idle jobs that flash a panel light in some recognizable mode. System programmers often become very familiar with these light patterns and can tell from them how busy the system is and, sometimes, exactly what it is doing right now. Master Control Program for Burroughs Corporation B6700 mainframe will display the uppercase "B" when the system is in idle state.

Switches and lights require little additional logic circuits and usually no software support, which is important when expensive hardware logic components and software are often limited.

This baroque front panel style began to go off in 1964 when Seymour Cray designed its CDC 6600 supercomputer with a very simple and elegant display console containing only two CRT screens and a keyboard, replacing all the hundreds of flashing switches, buttons, and lights. The 6600 has the support of ten "peripheral processors" supporters whose job includes reading the keyboard and moving the graphic display.

Early microcomputers such as the 1975 Altair 8800 also rely on the front panel, but since the introduction of the Apple II, TRS-80, and Commodore PET during the home computer boom of 1977, most microcomputers are equipped with keyboards and connections for screen TVs or other monitors.

Maps Front panel

General use

An operator will use the front panel to bootstrap the computer, to debug the running program, and to find hardware errors.

Boot

Normally, the operator will have a written procedure that contains a series of short bootstrap instructions that will be entered manually using the toggle switch. First, the operator will set the switch "address" and put the address in binary using the switch. For easier entry and readings, on some computers (such as the DEC PDP-8 or MITS Altair 8800 binary digits) are grouped into three sections on the front panel, with each light or switch group representing an octal number between 0 and 7. Decimal computers like the IBM 1620 use decimal-coded binaries for memory addresses.

The operator will then set the "value" switch, and then enter the value intended for that address. After entering some of these instructions (most computers have a "next deposit" button, which will store the next value at the next address, reducing the operator that needs to switch in the address), the operator will then assign the start address of the bootstrap program and press "run" button to start program execution. The bootstrap program usually reads programs that are somewhat longer than hollow paper, hollow cards, magnetic tapes or disks which in turn will load the operating system from the disc.

Some machines speed up the bootstrap process by allowing the operator to set the switch to load one or two machine language instructions and then immediately execute the instruction. Other machines allow I/O devices to be explicitly instructed from the front panel (eg, "Read-In Preset" on the PDP-10 or accessing memory I/O devices in PDP-11). Some machines also contain various bootstrap programs in ROM and all that is required for the system boot is running it in the correct ROM program address.

Debugging

The front panel is often used to debug programs when support operations are limited and most programs run in stand-alone mode. Usually the front panel switches can cause a one-step computer, which runs a single instruction and stops until the programmer presses a button to execute the next instruction. A stop address can be set to stop running programs while trying to execute instructions or access data at a particular address. The contents of the register and memory will be displayed on the front panel lights. The programmer can read and change the contents of the register, change the program or data instruction in memory or force the branch to another part of the code.

When multiprogramming becomes the norm it is no longer acceptable to bind the entire machine to debugging, except for special situations. Programs called debugger are written which provides programmers with equivalent front panel functionality without requiring the whole machine.

Entertainment

For fun, a bored programmer will create a program to display an animated light show. The front panel in the late 1960s and early 1970s was quite brightly colored. When the bootstrap ROM enabled the computer to start itself without operator intervention in the late 1970s and early 1980s, most computers were built without a front-panel switch. High-powered calculators, such as the ROM-based HP 9830, are among the first computers to get rid of the front panel, and the operator.

The big banks "blinkenlights" and "blowenfuzen" were featured on TV and movies as popular images of "computers" during the 1950s to 1970s. (A Burroughs B205 is used as a Hollywood supporter for many of these events.)

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Example

The following procedure will bootstrap the PDP-8 system from the moving-magnetic disk of RK05:

1. Make sure that the machine is stopped by lowering and raising the Stop switch; "RUN" front panel lights should be turned off.
2. Set 12 data switches to 0030 (Octal address 30), press the Load Address ("ADDR LOAD") button. The address light will change to "0030".
3. Set the switch to 6743, raise the deposit switch. The data light will show this instruction.
4. Set the switch to 5031, raise the switch Deposit . The data light will show this instruction.
5. Set the switch to 0030 (Octal address 30), press the Load Address button. The address light will change back to "0030".
6. Press the Clean button.
7. Press the Continue button. The "RUN" light will be lit and the operating system on the disk will bootstrap.

This process works by depositing a simple two-instruction program in memory and executing it. The first instruction instructs the disk controller to start reading the disk from the current disk address to the current memory address. The second instruction is a JMP instruction that jumps to itself nonstop. When "Delete" is pressed, the current disk controller disk address is set to sector 0 and the current memory address is set to memory location 0000. When the read command, the program stored in the disk sector 0 overlays the bootstrap program and, once the JMP instruction is overlayed, take control of the machine.

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References

Source of the article : Wikipedia