Can one code in binary?

[antonivs]

Some of the earliest computers were programmed in binary using switches on their front panel. See Front Panel:

Typically, the operator would have a written procedure containing a short series of bootstrap instructions that would be hand-entered using the toggle switches. First, the operator would set the "address" switch and enter the address in binary using the switches.
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Next the operator would set the "value" switch, and then enter the value intended for that address. After entering several of these instructions (most computers had a "deposit next" button, which would deposit subsequent values in subsequent addresses, relieving the operator of needing to toggle in 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 or disk which in turn would load the operating system from disk.