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The ID blocks are created at the time the disk is formatted. When a file is deleted, FCS will shuffle down all of the files which come after it in the directory, repacking the directory and transferring the later file contents to fill the created gap. Because it takes quite a lot of cycles to establish that the correct sector was discovered and to modify the state of the write line, there is some ambiguity of when the minimize-over will happen. Because files are solely ever appended to the listing, saving FOO.BAS to disk, editing it a bit, then saving it again will result in two entries: FOO.BAS;1 and FOO.BAS;2. Although it was basically a personality oriented show (not bitmapped), it was potential to combine textual content of two totally different sizes with 128x128 graphics in eight different colors. Because it used the raw 5501 serial knowledge stream, in the worst case there is perhaps eight '0' data bits following the '0' start bit earlier than the final '1' stop bit. In a single mode, the chip operated as meant, and drove the RS-232 serial port, permit the same old range of hyperlink speeds (one hundred ten bps to 9600 bps) and stop bit choices.

The 5501 has a simple RS-232 type serial interface: one start bit, 8 knowledge bits, one stop bit, costing 10 bits per byte. CP/M did not have this and thus it was only a software convention to someway sign the last significant byte of the file, eg -Z in a textual content file. It means the info stream might have long-time period DC content, yet the recording medium is incapable of tracking it; it additionally implies that there are not any unlawful bit encodings, such that there aren't any easy to differentiate encodings to use to sync to; it additionally signifies that the learn logic can't use AGC (automated gain control) and should have an absolute threshold for distinguishing a one bit from a zero bit. Without any simple sync token, how can the system tell the place a sector begins? FCS (the File Control System) routines deal with the disk as 400 sectors, rather than a track/sector addressing scheme. In fact, the person was warned that in the event that they misprogrammed some of the timing registers, it may harm the CRT management electronics. Timing was managed by a SMC 5027 CRT timing controller.

The unit didn't shield the drive at all, putting the r/w head and associated analog amplifier and sign conditioning circuitry inches away from a excessive voltage CRT and likewise the switching power provide. Subsequent write operations overwrite the data block however do not touch the ID block associated with a given sector. Once the best track and sector are discovered, the software switches on the write allow and then writes the info block. To unravel this, the formatter writes three dummy 0xFF bytes between the ID block and the info block. If multiple sector is allotted for the listing (the default is three sectors), every subsequent block contains six file listing entries. The first file seems immediately after the last sector reserved for the listing entries, and is allocated contiguously. The next file seems immediately after that. Instead, it appears to maneuver one file at a time. Instead, a small 32 byte PROM, read in from 8080 input port 0x80 to 0x8F, offered the timing values. FCS views the disk as 400 sectors, sector zero through sector 399. Sector 0 starts with a small descriptor indicating how many sectors are for use for the disk listing, and likewise contains a ten byte quantity label.

All sectors after the final file are "free", and are used when the next file is written. Because there are forty tracks in use and each monitor has 10 sectors per observe, there are four hundred sectors complete. Being a single sided drive with 40 used tracks, the entire capacity of the drive was 51,200 bytes. The disk has 41 tracks, but observe 0 incorporates nothing and is not utilized by the system. If the disk velocity is off by a few p.c, particularly if the system which wrote the sector was different than the system reading it, bits might be dropped or inserted. Most different system have a tiny ROM routine to learn a boot sector from the disk, which then loads in a 2nd stage disk operating system, permitting for bug fixes and enhancements after the actual fact. Each sector begins with about 10 byte instances (a hundred bits, or 130 us) of hole -- nothing however mark ('1') state and no transitions.

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