Simplest (practical) file system?

Sean 'Captain Napalm' Conner wrote: 1. The smallest ammount of data read or written to disk is 1024 words. This value is used due to the HP 1000's paged memory design on all CPU's, as well as the virtual memory scheme on the late model 21MX processors. All disk drivers 'translate' hardware tracks and sectors into 1024 word 'blocks', so all O/S level disk address calculations are indentical to VM page address calculations. (in fact, they are the very same routines) Data is always word-aligned, although 21MX CPU's do support byte (limited) addressing. As for 'placement' issues, HP's can only 'see' the current 1024 word 'page', and page zero, not unlike a 16-bit PDP-8 with larger pages and extra registers. There are only 32 pages at a time, but you can have 2 mappings of physical memory (up to 1024 K words) to logical memory (the 32 pages). Transfers to and from disk do not need to be block boundry aligned. The current plan (quickly evolving) is to support two disk buffers, each of 1024 words. Only two files can be attached at one time without thrashing, but a rather unique method of saving the file access pointer for each file in the directory structure. This was a file can be opened, accessed, then closed, and re-opened at the point of last access + 1, or you can open the file at the start and seek to any point in the tranditional method. Your getting to the real issues here! First, the average file size, I do not beleive we really know at this point. Lets look at the file types first, and then look at the relative file sizes. The first, and most primative file type the O/S understands is an ABS binary image. This is a variable length string of 8-bit bytes in a blocked, raw binary format with checksums and block addresses. These images describe an absolute addressed binary image which cannot hold more than 32K words. So the maximum practical ABS file size is somewhere around 75 kb. But ABS images must be processed on the fly, during load time, so DMA is not an option. The result is that ABS files are not a practical disk format. But ABS is the format HPdistributed their early software in (like HP Basic, etc). ABS is really a paper-tape format, best used with hardware emulators as ultra-fast boot devices. Once an ABS image is loaded into memory, it can be saved directly to disk in a raw binary format for fast DMA transfers. These ram binary image files are never longer than 32K words. This is the disk boot format. So once you boot either an ABS image from a paper tape reader emulator, or a raw binary file from a disk device and you have the programming language / operating system running we have a bare-bones system with free memory. At this point you can load IPL source code into the comand line interpreter and 'compile' definitions in the dictionary to provide new keywords for hardware device drivers, floating point package, or other optional and customized functions to taylor the running image for your application. So once the engine is loaded into memory and running it needs to read a series of 'library' files. These are ASCII IPL source code files and are generally a few K bytes at most. It may be practical to place many named definitions inside one disk 'file', and then call them by name from a common library file. Of course we want to support general data files for the programmers use at well.