WHAT DOES THE HFS FILE SYSTEM LOOK LIKE SERIAL
WHAT DOES THE HFS FILE SYSTEM LOOK LIKE CODE

Applications could then make calls to the OS instead of using their own routines to do such things, which reduced programming complexity and probably helped reduce code size or execution time (because those system facilities could be heavily optimized and debugged once after which everyone would benefit). Things like file, disk and printer I/O were probably among the first to be collected into what is now known as an operating system, followed by process scheduling (it's worth noting that the early-1960s Apollo Guidance Computer was a multitasking computer). In the old days, operating systems were simply a collection of those 'useful routines' that each application otherwise would have to rewrite from scratch, and computers were essentially batch processing devices. However, there's no reason why the application that uses those facilities has to be a shell. The shell, whether a graphical shell, command line interpreter or something else, uses the facilities provided by the operating system to do things like read commands, launch processes, do I/O redirection and so on. Take for example the Linux kernel's diagnostic output during the boot and kernel initialization process. As Oliver Salzburg mentions, it would probably just show a blank screen (if it has display output support at all), though there's no reason it'd have to. That's diving into the realm of electronics and I admit I don't know very much about it, except that my GuruPlug comes with one and I can directly program the flash chip on the GuruPlug's board with it - meaning if something kills the bootloader on the GuruPlug, I have a 'CPU independent' way of flashing it back.ДЄn operating system doesn't have to provide a shell as the term is commonly used today (meaning an application which will accept commands interactively from the user), but such an operating system won't really 'look like' anything at all to the user. Terminal emulator or is there no way going behind a shell?

WHAT DOES THE HFS FILE SYSTEM LOOK LIKE SERIAL

Some bootloaders such as U-Boot can be accessed via the serial port.Д«ootloaders don't run 'behind' the OS, they load the OS, hand control to it, and then they are no longer running. Here, pre-boot utilities can exist, or a minimal mechanism for loading such utilities exists. Keep in mind that for a long time most computers have been expected to have ROM or firmware that takes control of the system when it is turned on before it hands it off to an OS. I believe most if not all modern CPUs have a 'JTAG port' which allows the same type of direct operations. I am no expert in this area but old, old computers like the Altair, IMSAI, and PDP-8 and such had front panel switches that directly controlled the CPU and could directly read and write memory without CPU intervention. If a computer cannot even accept commands (there is no command line), If you wanted to run a different program you had to do this over. This is batch processing as opposed to interactive processing. The CPU would run this program, generate its output, and stop. UNIXД®ssentially (and leaving out a lot but this should get you the idea) - You loaded your program, either by flipping switches on a panel or using a paper-tape reader (these devices would write to memory directly without CPU intervention) and then start the CPU with another switch. How were systems used before the first shell was developed (e.g. Many operating systems support outputting boot and diagnostic information to some form of UART, which may somehow be available on the unit even if hidden from the user (google 'Add serial port to DD-WRT' for examples of where manufacturers hide serial ports and how you can get to them).ДЄn OS doesn't have to have an external display at all - it's just another device to the OS.

Some OS's/systems may write diagnostic information to a non-volatile memory that can be accessed by putting the system in developer, debug, or diagnostic mode. It can also be configured to be perfectly silent. Linux can be configured to write boot text to a console device, whether a text mode console, framebuffer console or a serial port. What does an operating system look like before a shell is run?Дepends on the OS and how you configure it.

What does the hfs file system look like