Reconstruct Google Code wiki history from r394 on 2014-01-19.

WebUIUsingTheMagTapeDrive.wiki

@@ -9,7 +9,7 @@ The B5500 supported several 7-track tape drive models, with recording densities
 
 All drives could record in even or odd parity. With even parity (also termed alpha mode), characters were translated to and from BCL (Burroughs Common Language), which was very similar to the character codes used with IBM 1401 tape drives. With odd parity (binary mode), bits were recorded without translation from their internal representation in the B5500 core memory.
 
-A B5500 system could support 16 tape drives, identified as `MTA` through `MTT` (with letters `G`, `I`, `O`, and `Q` not used).
+A B5500 system could support up to 16 tape drives, identified as `MTA` through `MTT` (with letters `G`, `I`, `O`, and `Q` not used).
 
 Here is a view of a B42x-series drive with its front door open, showing the tape head, pinch-roller mechanisms, and tape columns:
 
@@ -24,12 +24,12 @@ The tape drive interface we have developed for the web-based emulator is modeled
 
 The B425 had additional buttons and lights for power on/off, but these controls are not relevant to operation under the emulator.
 
-A 2400-foot reel of tape could hold approximately 2-20 million characters depending on the size of the blocks recorded. A typical capacity was 10-15 million characters.
+A 2400-foot reel of tape could hold approximately 2-22 million characters depending on the size of the blocks recorded. A typical capacity was 10-15 million characters.
 
 Data for tape volumes ("reels") may be maintained externally as ordinary workstation files. Such a file is referred to as a "tape image." This tape drive implementation supports the following tape image formats:
 
     * *"`.bcd`"* -- In this format, each 7-bit frame on the tape is stored in one 8-bit byte. The low-order six bits of the byte contain the data, low-order bit last. The seventh bit is parity. The high-order bit in the byte is a one if this frame starts a physical block on the tape. A tape mark (end-of-file indicator) is represented by a single-frame block with the hexadecimal value 8F (i.e., an even-parity BCL greater-than-or-equal character). The same tape mark encoding is used with both even and odd parity recording.
-    * *Text* -- In this format, the tape image is a standard text file. Each 7-bit frame on the tape is stored as one ASCII character. Each physical tape block is represented as one line of text in the image file. Lines of text may be delimited by a carriage-return, a line-feed (newline), a form-feed, a carriage-return/line-feed pair, or a carriage-return/form-feed pair. A tape image can be loaded into the system as either even or odd parity, but the characters in the text image are represented the same either way. A tape mark is represented by a line with a single "`}`" (greater-than-or-equal) character. Note that in this format, the length of a tape block is determined by the length of its ASCII line of text, so trailing spaces are significant, and tab-compression may not be used.
+    * *Text* -- In this format, the tape image is a standard text file. Each 7-bit frame on the tape is stored as one ASCII character. Each physical tape block is represented as one line of text in the image file. Lines of text may be delimited by a carriage-return, a line-feed (new-line), a form-feed, a carriage-return/line-feed pair, or a carriage-return/form-feed pair. A tape image can be loaded into the system as either even or odd parity, but the characters in the text image are represented the same either way. A tape mark is represented by a line with a single "`}`" (greater-than-or-equal) character. Note that in this format, the length of a tape block is determined by the length of its ASCII line of text, so trailing spaces are significant, and tab-compression may not be used.
 
 Lines of text for a tape image should be composed using the emulator's version of the B5500 64-character set:
 
@@ -47,20 +47,20 @@ Lines of text for a tape image should be composed using the emulator's version o
 The B5500 used five special Algol characters that do not have ASCII equivalents. The emulator uses the following ASCII substitutions for them:
 
     * `~` for left-arrow
-    * `|` for "×" (the multiplication sign)
+    * `|` for "×" (the multiplication sign)
     * `{` for less-than-or-equal
     * `}` for greater-than-or-equal
     * `!` for not-equal
 
 The tape drive interface will translate lower-case ASCII letters to upper case. All other ASCII or Unicode characters will be considered to be parity errors in a tape frame.
 
-By default, the B5500 MCP brackets each file on the tape with 80-character label records. These label records serve to identify the tape reel and file names, and to provide record size and block size information, plus creation and expiration dates for the tape.
+By default, the B5500 MCP brackets each file on the tape with 80-character label records. These label records serve to identify the tape reel and file names, and to provide record size, block size, creation date, and expiration date for the tape.
 
 Tape files have a two-part name, the MFID (multi-file identifier) which is the same for all files on one logical volume, and the FID (file identifier), which is intended to uniquely identify the file within the logical volume. Each of these names can be up to seven characters in length. A logical tape volume can extend across multiple physical reels of tape.
 
 This two-level naming convention was first established for tapes on the B5000, and later carried into the design of the B5500 MCP disk directory. It eventually made its way into the design of the disk directory for Gary Kildall's CPM operating system.
 
-When a tape is mounted on a drive and the drive made ready, the MCP will automatically read the label and automatically assign the drive to a program that has asked for a file by the names specified on the label. If only the MFID matches, the MCP will automatically search up-tape for a file with the matching FID. Unlabeled tapes are also supported by the MCP, but are less convenient, as they usually need to be assigned manually to a program using the SPO `UL` command.
+When a tape is mounted on a drive and the drive made ready, the MCP will automatically read the label and assign the drive to any program that has asked for a file by the names specified on the label. If only the MFID matches, the MCP will automatically search up-tape for a file with the matching FID. Unlabeled tapes are also supported by the MCP, but are less convenient, as they usually need to be assigned manually to a program using the SPO `UL` command.
 
 Tapes marked as "scratch" will be assigned automatically to programs requiring an output tape.
 
@@ -70,18 +70,18 @@ Tapes marked as "scratch" will be assigned automatically to programs requiring a
 The user interface for the emulated tape drive consists of the following controls and indicators:
 
     * *UNLOAD* -- this black button is used to unload a tape image from the drive. This button is active only when an image is currently loaded, the drive is in local status, and the tape is positioned at BOT.
-    * *LOAD* -- this black button is used to load a tape image into the drive as if it were a reel of tape. The button is active only when no image is currently loaded into the drive. Clicking this button will bring up a tape loader dialog to select an image file, as described below.
+    * *LOAD* -- this black button is used to load a tape image file into the drive as if it were a reel of tape. The button is active only when no image is currently loaded into the drive. Clicking this button will bring up the tape loader dialog to select an image file, as described below.
     * *LOCAL* -- this yellow button/indicator lights when the drive is in a not-ready status. The drive becomes ready when a tape image is loaded and the *REMOTE* button is pressed. It becomes not-ready when this button is pressed.
     * *REMOTE* -- this yellow button/indicator lights when the drive is in a ready status. The drive becomes ready when a tape image is loaded and this button is pressed. It becomes not-ready when the *LOCAL* button is pressed.
-    * *WRITE RING* -- This red button/indicator is used to signal and control whether the tape image that is currently mounted is enabled for writing. When this button is activated (the indicator is lit), the image is writable. Writable status can only be set (i.e., the write ring can be inserted) during the process of loading a tape image. Writable status can be reset (i.e., the write ring can be pulled) at any time while an image is loaded, even while it is in use.
+    * *WRITE RING* -- This red button/indicator is used to signal and control whether the tape image that is currently mounted is enabled for writing. When this button is indicator is lit, the image is writable. Writable status can only be set (i.e., the write ring can be inserted) during the process of loading a tape image. Writable status can be reset (i.e., the write ring can be pulled) at any time while an image is loaded, even while it is in use.
     * *REWIND* -- pressing this black button will rewind the tape image to its load point at the beginning of the image. The button is active only when a tape image is loaded into the drive and the drive is in local status.
 
 When a tape image is loaded into the drive, an icon representing a reel of tape will appear next to the rewind button.  While not shown on the picture above, there are white annunciators along the right edge of the panel showing the status of the tape image:
 
     * *UNLOADED* -- indicates that no tape image is currently loaded into the drive.
     * *AT BOT* -- indicates that a tape image is loaded and is currently positioned at the beginning of the tape or "load point."
-    * *AT EOT* -- indicates that a tape image is loaded and is currently positioned at its end. No tape movement forward from this position is permitted.
-    * *REWINDING* -- indicates that the drive is currently rewinding to the load point of the image.
+    * *AT EOT* -- indicates that a tape image is loaded and is currently positioned past the reflective end-of-tape marker.
+    * *REWINDING* -- indicates that the drive is currently rewinding to the load point (BOT) of the image.
 
 Below the buttons is a text area. This is initially blank, but after a tape image is loaded into the drive it will display either the name of the image file that was loaded, or "`(blank tape)`" if a blank image was loaded.
 
@@ -96,7 +96,7 @@ Before a tape drive can be assigned to a user program or the MCP, a tape image m
 
 There are two types of tape images that can be loaded into the drive: an image from an existing file, and a blank image.
 
-    # To load an image from an existing file, use the file picker control at the top of the dialog to select the file from your local file system. The interface will infer the type of image format from the file name extension:
+    # To load an image from an existing file, use the file picker control at the top of the dialog to select the file from your local file system. The interface will infer the type of image format from the file name extension as follows:
         * "`.bcd`" implies a ".bcd" tape image.
         * Anything else implies and "ASCII Odd Parity" text image.
     # To load a blank image into the drive, do not use the file picker control. Select "`(blank tape)`" from the *Format* drop-down list. This is the default setting when the loader dialog opens.
@@ -110,24 +110,28 @@ Once a tape image is selected, there are two optional controls that you may use:
     * *Write Ring* -- checking this box will make the image writable and illuminate the Write Ring button on the tape drive window. When loading a blank tape image, this setting will be forced.
     * *Tape Length* -- selecting an item from this drop-down list will specify the total length of the tape image. This is significant only when the *Write Ring* box is checked and the image is to be writable. The drop-down list of tape lengths is disabled otherwise. There are three choices for length: 600 feet, 1200 feet, and 2400 feet (the default), corresponding to the most common reel sizes that were used for 7-track magnetic tape. If an image file is larger than the selected length, the actual image length plus 20 feet will be used instead.
 
-You can select only one file at a time to load into the drive. The drive does not attempt to verify that any file you load is a valid tape image. An invalid image file or a mismatch between the selected format and the image data will generally result in parity errors during read operations.
+You can select only one file at a time to load into the drive. The emulator does not attempt to verify that any file you load is a valid tape image. An invalid image file or a mismatch between the selected format and the image data will generally result in parity errors during read operations.
 
 Once you have the parameters for the tape image specified, click the *OK* button to complete the load process, or click *Cancel* to abort the load and leave the drive in an unloaded state. Clicking either of these buttons will cause the loader dialog to close.
 
+After the tape image is loaded into the drive, the drive will remain in the local (not-ready) state. You must press the *REMOTE* button to make the drive ready and available to the MCP.
+
 
 == Unloading a Tape Image ==
 
-If you load a tape image into the drive with its write ring enabled, and the system actually writes on that image, then when you unload the image from the drive the emulator will offer you the option to save the image.
+If you load a tape image into the drive with its write ring enabled, and the system actually writes on that image, then when you unload the image from the drive the emulator will offer you the option to save the image. Note that when the write ring is enabled, any writes to the tape do not affect the file from which you loaded the tape image. All tape operations affect only the internal tape image data resident in memory.
 
 If the image is read-only or has not been written to, clicking the *UNLOAD* button will simply discard the internal image data and leave the drive in an unloaded state.
 
-If the image has been written to, clicking the *UNLOAD* button will cause a dialog box to open, asking whether you want to save the image data. If you click *Cancel* on this dialog, the internal image data will be discarded and the drive set to an unloaded state, as above.
+If the image has been written to, clicking the *UNLOAD* button will cause a dialog box to open, asking whether you want to save the image data. 
 
-If you click *OK* on this dialog, the emulator will open a blank window and format the final contents of the internal tape image to that window as an ASCII text image. For full tape images, this conversion from the internal .bcd format to ASCII text may take several seconds. Once the tape image data is displayed in the window, you may save the contents to a text file on your local workstation or copy/paste the text into another program, such as a text editor. If you choose to do the latter, you should disable any options in your editor that will trim trailing blanks from lines or compress multiple spaces using tab characters, as these may corrupt the image.
+    * If you click *Cancel* on this dialog, the internal image data will be discarded and the drive set to an unloaded state, as above.
+    * If you click *OK* on this dialog, the emulator will open a blank window and format the final contents of the internal tape image to that window as an ASCII text image. For full-tape images, this conversion from the internal ".bcd" format to ASCII text may take several seconds. 
+    * Once the tape image data is displayed in the window, you may save the text to a file on your local workstation or copy/paste the text into another program, such as a text editor. 
+    * If you choose to paste the text into another program, you should disable any options in that program that will trim trailing spaces from lines or compress multiple spaces using tab characters, as these may cause the image to become corrupted.
+    * Once you have saved or copied the tape image data, simply close the window that was opened by the *UNLOAD* button.
 
-Once you have saved or copied the tape image data, simply close the window with the tape image data.
-
-Note that regardless of the format of the image you loaded into the drive, unloading and saving the internal image data will always be done using the ASCII text format. Other formats involve binary data with non-printing characters, which at present is not practical to output from a web browser.
+Note that regardless of the format of the image you loaded into the drive, unloading and saving the internal image data will always be done using the ASCII text format. Other formats involve binary data with non-printing characters, which at present is not practical to output from a web browser to your local environment.
 
 
 = Operating the Magnetic Tape Drive =
@@ -138,9 +142,9 @@ Tape output is generally possible only to "scratch" volumes, which may be create
 
 You can stop the drive at any time and make it not-ready by pressing the *LOCAL* button. Restart it by pressing the *REMOTE* button. Whenever the drive is in a not-ready status, you can rewind or unload the tape image.
 
-We now recommend that, when using the Cold Loader script to initialize the emulator's disk subsystem, you load only the minimum necessary set of system files to disk using the Cold Loader, and load any additional files using Library/Maintenance once the MCP is up and running. The MCP does a much better job of disk space allocation and directory maintenance than the Cold Loader. In particular, the MCP will replace existing files safely. It will also try to evenly distribute files across the available disk EUs, which will tend to more evenly distribute I/Os across the EUs and enhance throughput by increasing the probability of multiple simultaneous I/Os taking place.
+When using the [WebUIGettingStarted#Cold-starting_the_System Cold Loader script] to initialize the emulator's disk subsystem, we now recommend that you load only the minimum necessary set of system files to disk using the Cold Loader, and load any additional files using Library/Maintenance once the MCP is up and running. The MCP does a much better job of disk space allocation and directory maintenance than the Cold Loader. In particular, the MCP will replace existing files safely. It will also try to evenly distribute files across the available disk EUs, which will tend to more evenly distribute I/Os across the EUs and enhance throughput by increasing the probability of multiple simultaneous I/Os taking place.
 
-Library/Maintenance is the portion of the MCP that manages disk files and maintains the disk directory. Among its features is the capability to dump disk files to and load disk files from magnetic tape. This was typically used for file backup, archiving, and transferring files among systems.
+Library/Maintenance is the portion of the MCP that manages disk files and maintains the disk directory. Among its features is the capability to dump disk files to and load disk files from magnetic tape. This is typically used for file backup, archiving, and transferring files among systems.
 
 Disk files can be loaded from Library/Maintenance volumes such as the `SYSTEM`, `SYMBOL1`, and `SYMBOL2` tape images using the `LOAD` and `ADD` control card commands, e.g.,