DECtape - Revision history

Jnc: New cat

2022-05-30T12:21:57Z

New cat

Jnc: /* External links */ +DECtape documents at BitSavers

2021-10-18T21:22:02Z

‎External links: +DECtape documents at BitSavers

Jnc: Avoid redirs

2021-10-18T13:58:42Z

Avoid redirs

Larsbrinkhoff: Type 555.

2021-08-24T12:49:40Z

Type 555.

Larsbrinkhoff: PDP-6, 7, 9 too.

2021-08-24T12:45:54Z

PDP-6, 7, 9 too.

Jnc: /* External links */ +maintenance issues note

2021-08-24T08:38:00Z

‎External links: +maintenance issues note

Jnc: /* External links */ +3M spec

2021-08-23T20:37:09Z

‎External links: +3M spec

Jnc: +links, better cat

2021-08-22T08:01:15Z

+links, better cat

Jnc: fix link

2019-11-22T21:08:49Z

fix link

Jnc: +cat

2018-12-16T15:25:26Z

+cat

@@ Line 48: / Line 48: @@
 ** [http://www.bitsavers.org/pdf/dec/dectape/3M_DECtape_Spec_Nov66.pdf Scotch<sup><font size="-2">TM</font></sup> Magnetic Tape for Instrumentation]
-[[Category: DEC Tape Drives]]
+[[Category: Magnetic Tape]]
-[[Category: Tape Drives]]
+[[Category: DECtape]]

@@ Line 44: / Line 44: @@
 ==External links==
-* [http://www.bitsavers.org/pdf/dec/dectape/CJL_DECtape_20070117.txt TU55/TU56 issues] - Drive mechanical maintenance issues
+* [http://www.bitsavers.org/pdf/dec/dectape/ DECtape]] - DECtape documents at BitSavers
-* [http://www.bitsavers.org/pdf/dec/dectape/3M_DECtape_Spec_Nov66.pdf Scotch<sup><font size="-2">TM</font></sup> Magnetic Tape for Instrumentation]
+** [http://www.bitsavers.org/pdf/dec/dectape/CJL_DECtape_20070117.txt TU55/TU56 issues] - Drive mechanical maintenance issues
 [[Category: DEC Tape Drives]]
 [[Category: Tape Drives]]

@@ Line 11: / Line 11: @@
 The drive had a single [[head]], and used hydro-dynamic lubrication to reduce wear on the tape; like disk heads, the tape floated on a layer of air while the tape was moving, without touching any metal. (In a test, a tape made 30,000 passes over a head without significant wear.)
-DEC produced two DECtape drives; the single [[TU55]], and the dual [[TU56]]. [[Device controller|Controllers]] for them existed for the [[PDP-7]], [[PDP-8 family|PDP-8]], [[PDP-9]], [[PDP-10]], [[PDP-11]] and [[PDP-15]], among others. The older Type 555 Dual Microtape Transport was used with the [[PDP-1]], [[PDP-4]], [[PDP-5]], and [[PDP-6]].
+DEC produced two DECtape drives; the single [[TU55 DECtape Transport]], and the dual [[TU56 DECtape Transport]]. [[Device controller|Controllers]] for them existed for the [[PDP-7]], [[PDP-8 family|PDP-8]], [[PDP-9]], [[PDP-10]], [[PDP-11]] and [[PDP-15]], among others. The older Type 555 Dual Microtape Transport was used with the [[PDP-1]], [[PDP-4]], [[PDP-5]], and [[PDP-6]].
 ==History==
@@ Line 19: / Line 19: @@
 Although almost compatible (the drives on the [[PDP-12]] could support both LINC tapes and DECtapes), there were minor differences between the two: e.g. the location of the feed and take-up reels were reversed between the two, and the mark track format differed considerably, to support bi-directional read and write (the LINC tape could read and write in the forward direction only).
-DECtape was originally called Microtape.  As a pun on this, IBM 7 and 9 track magnetic tape was sometimes called Macrotape.
+DECtape was originally called Microtape. As a pun on this, IBM 7 and 9 track magnetic tape was sometimes called Macrotape.
 ==Tape format==
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 Since each 'line' on the tape contained only three bits, a 12-bit word took four lines to store, and 16/18-bit words took 6 lines. (16-bit machines used 18-bit words on the tape, but normally ignored two of the bits.) Blocks were potentially of different sizes, but normally were all a single size: 128 12-bit words, 256 16/18-bit, or 128 36-bit words. A tape could hold 184K 12-bit words, or 144K 16/18-bit words.
-The block format included checksums, guard words to protect the block numbers, along with an inter-block zone. The tape format included end zones and extension areas on each end of the tape; the former was to prevent the tape running off the reels, and the latter to allow reel acceleration before reading/writing starts.
+The block format included [[checksum]]s, and guard words to protect the block numbers, along with an inter-block zone. The tape format included end zones and extension areas on each end of the tape; the former was to prevent the tape running off the reels, and the latter to allow reel acceleration before reading/writing starts.
 ==Specifications==

@@ Line 5: / Line 5: @@
 It used 3/4-inch wide [[magnetic tape]] on small 4-inch reels, formatted before use into fixed-sized blocks which could be individually read or written. This differs from conventional magnetic tape, which could only be written at the end of the previously-written area of the tape.
-DECtape was [[random access]], so the [[magnetic tape drive|drive]] had the ability to move forward and backwards to the desired block. The tape format included a block number at the start and end of each block, to help the drive find the desired block. Tapes could be read and written while moving in either direction, which meant that when seeking backwards to the target block, it was not necessary to bring the tape to a halt, and reverse it, before reading the data.
+DECtape was [[random access]], so the [[magnetic tape drive|drive]] had the ability to move forward and backwards to the desired block. The tape format included a block number at the start and end of each block, to help the drive find the desired block. Tapes could be read and written while moving in either direction, which meant that when seeking backwards to the target block, it was not necessary to bring the tape to a halt, and reverse it, before reading the data. Not all DECtape controllers supported reading in the reverse direction, however.
 DECtape also had exceptional reliability; it used a very simple and brute-force mechanism to produce that: it wrote all tracks in duplicate on each half (in width) of the tape. It was possible to punch a hole in a DECtape with a paper punch and leave the tape readable.
@@ Line 11: / Line 11: @@
 The drive had a single [[head]], and used hydro-dynamic lubrication to reduce wear on the tape; like disk heads, the tape floated on a layer of air while the tape was moving, without touching any metal. (In a test, a tape made 30,000 passes over a head without significant wear.)
-DEC produced two DECtape drives; the single [[TU55]], and the dual [[TU56]]. [[Device controller|Controllers]] for them existed for the [[PDP-6]], [[PDP-7]], [[PDP-8 family|PDP-8]], [[PDP-9]], [[PDP-10]], [[PDP-11]] and [[PDP-15]], among others. Not all DECtape controllers supported reading in the reverse direction, however.
+DEC produced two DECtape drives; the single [[TU55]], and the dual [[TU56]]. [[Device controller|Controllers]] for them existed for the [[PDP-7]], [[PDP-8 family|PDP-8]], [[PDP-9]], [[PDP-10]], [[PDP-11]] and [[PDP-15]], among others. The older Type 555 Dual Microtape Transport was used with the [[PDP-1]], [[PDP-4]], [[PDP-5]], and [[PDP-6]].
 ==History==

@@ Line 11: / Line 11: @@
 The drive had a single [[head]], and used hydro-dynamic lubrication to reduce wear on the tape; like disk heads, the tape floated on a layer of air while the tape was moving, without touching any metal. (In a test, a tape made 30,000 passes over a head without significant wear.)
-DEC produced two DECtape drives; the single [[TU55]], and the dual [[TU56]]. [[Device controller|Controllers]] for them existed for the [[PDP-8 family|PDP-8]], [[PDP-10]], [[PDP-11]] and [[PDP-15]], among others. Not all DECtape controllers supported reading in the reverse direction, however.
+DEC produced two DECtape drives; the single [[TU55]], and the dual [[TU56]]. [[Device controller|Controllers]] for them existed for the [[PDP-6]], [[PDP-7]], [[PDP-8 family|PDP-8]], [[PDP-9]], [[PDP-10]], [[PDP-11]] and [[PDP-15]], among others. Not all DECtape controllers supported reading in the reverse direction, however.
 ==History==

@@ Line 11: / Line 11: @@
 The drive had a single [[head]], and used hydro-dynamic lubrication to reduce wear on the tape; like disk heads, the tape floated on a layer of air while the tape was moving, without touching any metal. (In a test, a tape make 30,000 passes over a head without significant wear.)
-DEC produced two DECtape drives; the single [[TU55]], and the dual [[TU56]]. Controllers for them existed for the [[PDP-8]], [[PDP-10]], [[PDP-11]] and [[PDP-15]], among others. Not all DECtape controllers supported reading in the reverse direction, however.
+DEC produced two DECtape drives; the single [[TU55]], and the dual [[TU56]]. Controllers for them existed for the [[PDP-8 family|PDP-8]], [[PDP-10]], [[PDP-11]] and [[PDP-15]], among others. Not all DECtape controllers supported reading in the reverse direction, however.
 ==History==

← Older revision		Revision as of 15:25, 16 December 2018
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	[[Category: DEC Peripherals]]		[[Category: DEC Peripherals]]
		+	[[Category: Tape Drives]]