The Apollo missions had technology no more complicated than a pocket calculator. 

From link [**here**](http://www.hq.nasa.gov/alsj/a11/a11.1201-fm.html), there's an information about Apollo Guidance Computer (AGC)

> 
> The on-board Apollo Guidance Computer (AGC) was about 1 cubic foot with 2K of 16-bit RAM and 36K of hard-wired core-rope memory with copper wires threaded or not threaded through tiny magnetic cores. The 16-bit words were generally 14 bits of data (or two op-codes), 1 sign bit, and 1 parity bit. The cycle time was 11.7 micro-seconds. Programming was done in assembly language and in an interpretive language, in reverse Polish.
> 
> 
> 

So, I've stumbled upon some source code when I researched what was up there, and I've noticed great comments (eg. TEMPORARY, I HOPE HOPE HOPE)

```
VRTSTART    TS  WCHVERT
# Page 801
        CAF TWO     # WCHPHASE = 2 ---> VERTICAL: P65,P66,P67
        TS  WCHPHOLD
        TS  WCHPHASE
        TC  BANKCALL    # TEMPORARY, I HOPE HOPE HOPE
        CADR    STOPRATE    # TEMPORARY, I HOPE HOPE HOPE
        TC  DOWNFLAG    # PERMIT X-AXIS OVERRIDE
        ADRES   XOVINFLG
        TC  DOWNFLAG
        ADRES   REDFLAG
        TCF VERTGUID

```

The actual programs in the spacecraft were stored in [core rope memory](http://www.hq.nasa.gov/alsj/a11/a11.1201-fm.html), an ancient memory technology made by (literally) weaving a fabric/rope, where the bits were physical rings of ferrite material. "Core" memory is resistant to cosmic rays. The state of a core bit will not change when bombarded by radiation in Outer Space. 

**[Virtual Apollo Guidance Computer (AGC) software is also on GITHUB!](https://github.com/rburkey2005/virtualagc)**

[Some part of documentation is here.](http://www.ibiblio.org/apollo/)

Another sample of source code with great comments.

```
033911,000064: 32,3017    06037        FLAGORGY        TC       INTPRET      #  DIONYSIAN FLAG WAVING

    034090,000243: 32,3241    13247        BZF      P63SPOT4               #  BRANCH IF ANTENNA ALREADY IN POSITION 1
    034091,000244: 
    034092,000245: 32,3242    33254        CAF      CODE500                #  ASTRONAUT:     PLEASE CRANK THE
    034093,000246: 32,3243    04616        TC       BANKCALL               #                 SILLY THING AROUND
    034094,000247: 32,3244    20623        CADR     GOPERF1                               
    034095,000248: 32,3245    16001        TCF      GOTOP00H               #  TERMINATE
    034096,000249: 32,3246    13235        TCF      P63SPOT3               #  PROCEED        SEE IF HE'S LYING

    034101,000254: 32,3251    04635        TC       POSTJUMP               #  OFF TO SEE THE WIZARD ...
    034102,000255: 32,3252    74126        CADR     BURNBABY

```

My question here is this:

* How were the teams writing this much code able to make it functional given the tools at the time?

Because if you compile so much code that was used on Apollo 11... it'd take days, even weeks. I seriously doubt that programmers back then left everything to happen by chance.