GO.COM contained no program bytes at all – it was entirely empty. However, because GO.COM was empty, but still a valid program file as far as CP/M was concerned (it had a directory entry and file-name ending with .com), the CP/M loader, the part of the OS whose job it is to pull programs off disk and slap them into the TPA, would still load it!
So, how does this help? Well, using the scenario above:
the user exited WordStar
the user ran DIR (or whatever else they needed) and at some future point would be ready to re-run Wordstar
the user now ‘loaded’ and ran GO.COM
the loader would load zero bytes of the GO.COM program off disk into the TPA – starting at address 0100h – and then jump to 0100h – to run the program it just loaded [GO.COM]!
result – it simply re-ran whatever was in the TPA when the user last exited to DOS – instantly"
It also wasn't unusual to try and recover data from memory after a program crashed by launching a small program that dumped memory to disk. 100% reliable? No, but it was the best one sometimes had.
GO.COM contained no program bytes at all – it was entirely empty. However, because GO.COM was empty, but still a valid program file as far as CP/M was concerned (it had a directory entry and file-name ending with .com), the CP/M loader, the part of the OS whose job it is to pull programs off disk and slap them into the TPA, would still load it!
So, how does this help? Well, using the scenario above:
the user exited WordStar the user ran DIR (or whatever else they needed) and at some future point would be ready to re-run Wordstar the user now ‘loaded’ and ran GO.COM the loader would load zero bytes of the GO.COM program off disk into the TPA – starting at address 0100h – and then jump to 0100h – to run the program it just loaded [GO.COM]!
result – it simply re-ran whatever was in the TPA when the user last exited to DOS – instantly"
It also wasn't unusual to try and recover data from memory after a program crashed by launching a small program that dumped memory to disk. 100% reliable? No, but it was the best one sometimes had.