Lunar Lander? - That was a long, long, long time ago.
The guidance computer on Apollo 11's Eagle had 24k of ROM and only 1k of RAM with a clock speed of 1Mhz and could multitask. On descent to the Lunar Surface, the computer threw up a 1201 alarm. It had effectively run out of memory. It came up a second time (if memory serves me correctly) before throwing up a 1202 alarm. With 30 seconds of fuel, they had to use another piece of equipment to confirm their height. Then they spotted that the landing area had too many rocks, so Neil switches to manual, maintains height to fly past the boulder field and lands with 2 (IIRC) seconds of fuel left.
The computer was operated by entering verb noun pairs and running them. This was similar to @ULITE offering so I ran with the memory.