AMPEX TAPE TRANSPORTS

ring, and a drawing showing the location of the tape markers. Every transport requires a Data General adapter, which is mounted below a TMX or TMZ transport and inside the cabinet of a TM-16 transport. On the adapter are a power button and a thumbwheel switch for selecting the unit address.

The most important consideration in tape operations is cleanliness. Nothing can ruin a tape run more easily than ash, dust or a piece of dirt. The tape path should be cleaned at least once every eight hours.

Cleaning instructions are given in the Ampex manual.

TMZ Transport

Stop 6.4 4 Settle down _{~ ~}

Settle down 20 10 Total 52.2 30

Total 51.6 30.2

For 7-track add 10 6

For 7-track add 6.3 4.2

The rewind and fast forward speed is 150 inches per second; rewinding an entire reel takes about three minutes.

Controls for the transport are located on the adapter and at the upper left on the transport. The file-protect light at the top indicates when the data on the supply reel is protected from action by the program (the write enable ring is not in place). The remaining three controls at the top and bottom of the panel are alternate-action buttons which illuminate when on: POWER allows the operator to control transport power independently of the adapter; pressing REMOTE places the unit on line if the door is closed and tape is properly loaded; pressing STOP-RESET stops the tape and takes the unit off line. With the transport ,off line, holding down one of the four buttons in the center moves the tape at the speed and in the direction indicated; forward motion auto-matically terminates at the EOT marker, reverse motion at loadpoint. At the lower left corner inside the door are the density switch, an interlock, and a LOAD/UNLOAD button. When loading a tape, the operator must set the first switch to the density at which the tape will be processed; the program has no control over the density. Should the door be opened while the unit is running, the interlock stops the tape and takes it off line.

Pulling the switch out overrides the interlock, allowing operation with the door open. The LOAD/UNLOAD button is alternate-action and moves the tension arms to the loading or operating position. Cleaning instructions are given in §3.5.1 of the Ampex manual.

The illustrations below show the loading and operating tape configurations (supply reel at the top). Before loading a reel make sure it has no write enable ring if the data on the tape is not to be changed by the program;

LOADING CONFIGURATION OPERATING CONFIGURATION

otherwise place a ring in the reel so the transport can respond to write commands. To load a reel, tum the retainer knob on the reel hub to its counterclockwise limit, slip a reel onto the hub with the groove toward the tape deck, and holding the reel firmly, tum the retainer knob to its clockwise limit. Unwind about a foot of tape from the supply reel, thread it (as shown in the illustration) under the first edge guide, the tape cleaner head and the read-write head, and over the second edge guide. Bring the tape down and around the capstan and over the third edge guide. Pull the tape to unwind another foot, and wind about three turns around the takeup reeL Press LOAD/UNLOAD to generate tape tension, shut the d,?or, and press FOR WARD to locate the loadpoint; press REMOTE to put the unit on line. To unload the tape press STOP-RESET, rewind the tape to loadpoint, open the door, press LOAD/UNLOAD to release the tension arms, and tum the supply reel by hand counterclockwise to -unwind the rest of the tape. Tum the supply reel retainer knob counterclockwise and remove the reel from the hub.

TMX Tape Transport

This transport accommodates 81h-inch reels containing 1600 feet of tape (7-inch reels can be used, but they have only half the capacity). The tape processing speed is 12.5 inches per second; the time required to process each work at high density is 200 P.s, at low density 288 p.s. Interrecord times for 9-track tape are as follows.

Write interrecord times in ms Read interrecord times in ms

Start 37 Start 60

Last character to stop 12.5 Stop 5.7

Stop 12 Settle down 30

Settle down 30 Total 95.7

Total 91.5 For 7-track add 19

For 7-track add 12.5

The rewind speed is 75 inches per second; rewinding an entire reel takes about four minutes.

Controls for the transport are located on the adapter and on the left and right at the bottom of the trans-port front panel. When loading a tape, the operator must set the left toggle switch to the density at which the tape will be processed; the program has no control over the density. The tape can be threaded when the three-position toggle on the right is hitched into the DISABLE three-position; pressing the toggle to LOAD generates tape tension; it must be latched into RUN for normal transport operation. On the left panel are three lights that indicate when power is on, when the transport is ready for operation, and when the data on the supply reel is protected from action by the program (the write enable ring is not in place). The remaining controls are momentary-contact buttons. Pressing REMOTE places the unit on line if READY is lit; pressing STOP stops the tape and takes the unit off line (in either case the appropriate button is illuminated to indicate the transport condition). With the transport off line, holding down one of the remaining three buttons (on the right) moves the tape at the speed and in the direction indicated; forward motion automatically terminates at the EOT marker, reverse motion at loadpoint. Cleaning instructions are given in §3.5.1 of the Ampex manual.

The illustrations below show the loading and operating tape configurations (supply reel at the left).

Before loading tape make sure there is no write enable ring in the reel if the data on it is not to be changed by the program; otherwise install a write enable ring so the transport can respond to write commands. To load a reel, set the right toggll< switch to DISABLE, tum the retainer knob on the reel hub counterclockwise several turns, slip a reel onto the hub with the groove toward the tape deck, and holding the reel firmly, tum the re-tainer knob to its clockwise limit. Push the tape tension arms as far as they will go toward the center of the tape deck. Unwind about a foot of tape from the supply reel, thread it (as shown in the illustration) by the 4-13

first two tape guides (between them and the supply reel tension arm guide), around the left capstan, over the third guide, between the tape cleaner and photosense heads, over the read-write head and the fourth guide, around the right capstan and by guides 5 and 6 (between them and the takeup reel tension arm guide). Pull the tape to unwind about another foot, and wind about three turns around the takeup reel, making sure the tape is taut against the guides. Hold the right toggle switch to LOAD until tension arm motion ceases, and then set the switch to RUN. Shut"the door and press FORWARD to locate the loadpoint; press REMOTE to put the unit on line. To unload the tape press STOP, rewind the tape to loadpoint, and press REVERSE to wind all the tape onto the supply reel. Open the door, turn the supply reel retainer knob counterclockwise several turns, and remove the reel from the hub.

LOADING CONFIGURATION OPERATING CONFIGURATION

TM-16 Transport

This transport uses lOY2-inch reels and has a tape processing speed of 120 inches per second. The time required to process each word at high density is 21 /-'s, at low density 30 /-,s. Interrecord times for 9-track tape are as follows.

Write interrecord times in ms Read interrecord times in ms

Start 4 Start 6.5

Last character to stop 1.2 Stop .6

Stop 1.2 Settle down 5

Settle down 5 Total 12.1

Total 11.4 For 7-track add 2

For 7-track add 1.2

Rewinding an entire reel takes about 90 seconds.

The entire front of the cabinet is a door that covers the tape deck and vacuum columns, but the operator can gain access to the deck by lowering the window in the door. Controls for the transport are located on the adapter and on a panel at the top of the transport. The upper row on the panel contains three illuminated buttons and the file-protect light, which indicates when the data on the supply reel is protected from action by the program (the write enable ring is not in place). DENSITY is an alternate-action button containing two lights that indicate the density selected by the operator; when loading a tape, the operator must specify the density at which the tape will be processed, as the program has no control over it. The alternate-action POWER button allows the operator to control transport power independently on the adapter. The remaining buttons are all momentary-contact. Pressing REMOTE places the unit on line (lighting the button) if the window is closed

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and tape is properly loaded. Pressing RESET stops the tape and takes the unit off line, enabling the remaining buttons in the bottom row and allowing RESET to be used to raise (close) the window. After a tape has been threaded and attached to the takeup reel, pressing LOAD/REWIND loads it into the vacuum columns and moves it forward to loadpoint; if the tape is already loaded, this button rewinds it to loadpoint. Pressing UNLOAD rewinds the tape, pulls it out of the vacuum columns, winds it entirely on the supply reel, and lowers the window. Holding down either of the remaining buttons moves the tape at normal processing speed in the direction indicated; forward motion automatically terminates at the EOT marker, reverse motion at loadpoint. Cleaning instructions are given in §2.S.1 of the Ampex manual.

The illustration below shows the loading tape configuration (supply reel at the right). Before loading a reel make sure it has no write enable ring if the data on the tape is not to be changed by the program; other-wise place a ring in the reel so the transport can respond to write commands. To load a reel, press UNLOAD to lower the window, press the narrow part of the hub operating lever to release the hub lock, press a reel onto the hub with the groove toward the tape deck, and holding the reel firmly, press the wide part of the lever to lock the hub. Unwind several feet of tape from the supply reel, thread it outside the tape guides as shown in the illustration, and wind about three turns around the takeup reel. Press LOAD/REWIND to load the tape and press RESET to raise the window. Once the tape is in the vacuum columns and positioned properly, press REMOTE to put the unit on line. To unload a tape press RESET, press UNLOAD to lower the window and rewind the tape entirely on the supply reel, press the narrow part of the hub operating lever to release the lock, and remove the reel from the hub.

LOADING CONFIGURATION

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Chapter V Disk

A disk is generally the largest random-access storage device in a computer system (a single disk usually holds more bits than all of core), and it also provides the fastest storage outside of core. This makes the disk exceptionally desirable for backup storage for memory generally, and in particular, for swapping in time-sharing systems: while the currently active user programs are in core, inactive programs are stored on the disk. Unlike magnetic tape, a disk is constantly in motion and has a predetermined format with data blocks of fixed length. Hence reading and writing are the only disk operations, individual data blocks are addressable, and the average random access time is half a revolution. The Data General disk runs at 3600 rpm, giving an average latency time of 8.4 ms. Each disk can store 262,144 16-bit words in blocks of 256 words each. While a block is being processed, data transfers are at the rate of one word every 8 (J.s; the average transfer rate over a number of blocks is 57,835 words per second.

A disk system consists of a control and up to eight disks; each disk is a separate unit, and the control is contained on one standard circuit board that can be mounted in the computer chassis. The program com-municates with the control, which in turn governs all disks over a disk bus but comcom-municates with only one at a time. The control is connected to the data channel, so the program need only set up the disk system for reading or writing, and all transfers to and from memory are then handled automatically. To operate with the data channel the control has an address counter as well as data buffers (since all transfers are of fixed-length blocks, no word counting is necessary). The bus for a group of disks can also be connected to a second control, which in turn is connected to the IO bus and data channel of another computer, thus allowing com-munication between the two computers through disk storage.