OPERATING CHARACTERISTICS
Magnetic tape is normally used as an auxilliary storage device. In this capacity, large amounts of data may be stored for future reference and can be considered as permanent storage. Approximately 12 to 15 million 7 bit characters at high density can be stored on a 2400 ft. tape.
The B422 Magnetic tape units have a capstan speed of 120 inches/second and allows reading or writing at high or low densities. A special modification kit is
available to allow the 120 inch per second tape units to operate at 800 BPI. The character transfer rate is 96.0 KC.
The B423 tape units also have a capstan speed of 120 inches/second but the low density switch is locked in the low density position.
The B424 tape units have a capstan speed of 83.4 inches/s.econd and the density
$ele~t switch is locked in the very high density position. An interim B425 which is no longer available had a tape speed of 83.4 inches per second. Three tape densities were available.
The B425 tape units have a capstan speed of 90 inches/second and have a three
pos~tion density switch to allow character packing densities of low density, high density or very high density.
B421 Magnetic tape units have a capstan speed of 90 inches/second with high or low packing densities selection available to the operator.
Usually all tape units connected to the B5500 system have the same capstan speed even though different model numbers may be intermixed. Any I/¢ control may access anyone of 16 tape units. All tape units must function identically with any I/¢ control because only one set of tape control mu;Lti's for each density are contained in the I/¢. Tape units operating at 83.4 inches per second and tape units operating at 120 inches per second can be intermixed on the same system.
If this is done, the 120 inch per second units can operate only at 200 BPI or 555 BPI. In this case the set of 800 BPI multi's are adjusted to read tape with a capstan speed of 83.4 inches per second. These same multi's must be readjusted if 800 BPI are to be read when using a tape capstan speed of 120 inches per second. This is why one set of multi's cannot be used to read 800 BPI at two different tape speeds at the same time.
When mounting a tape reel, the operator must use the density select switch to select the corresponding density at which the tape read or write is to be per-formed. Consistent parity errors result on a tape read operation if the operator selects a density other than what the tape reel had previously been
written. Figure 5-1 shows the character transfer rate at different capstan speeds.
All tape units rewind 2400 ft., of tape in less than 90 seconds.
Printed in U.S. America 1-15-69 For Form 1036993
5-2
Burro-ughs - B5500 Input(Output Contro1l'raining ManualTAPE SPEED 90IPS 120lPS 83.41PS 83.4IPS 90IPS
200 BPI 18.0KC 24.0KC - 16.7KC 18.0KC
555 BPI 50.0KC 66.7KC - 46.3KC 5O.OKC
800 BPI - - 66.7KC 66.7KC 72.0KC
CHANNELS 7 7 7 7 7
MTU B 421 B422 B424 B425 B425
B9390 B9396 INTERMEDIATE 89391
FIGURE 5-1 TAPE TRANSFER RATE OPTIONS
The magnetic tape format uses standard 1/2 inch magnetic tape for data storage.
The physical placement of information in character form is shown in Figure 5-2.
READ
.005" @ 200 BPI .0018" @555.5 BPI .0012" @ 800 BPI
1 - - - -RECORD - - - I
1 - - - 6 " - - " ,
(67 MS)
SIDE CLOSEST TO OPERATOR
LONGITUDINAL PARITY GAP IS 4 1/2 CHARACTER FRAMES
1 - - - 3 / 4 " - - - . 1
RECORD GAP
- - - - T A P E MOTION WITH OXIDE SIDE Ur
FIGURE 5-2 MAGNETIC TAPE FORMAT INFORMATION CHARACTERISTICS
The tape format consists of 7 tracks, one of which is used fo.r vertical parity checking. Each vertical frame (7 tracks) comprises a character that may be.
written in three densities; low, high, or very high. A frame refers t.o a one bit space in each of seven channels. In alpha mode each frame represents an
Burroughs - B5500 Input/Output Control Train:ing Manual
alpha character (BCL code) of 6 bits plus an even parity bit. In binary mode each frame represents a binary character (internal code) of six bits plus an odd parity bit.
Alpha information is represented by character in the B5500. Each character consists of six bits: B, A,
4,
2, 1. With these six bits, there is a possible combination of bits to form 64 characters. These 64 characters are the alpha-betic characters A-Z, the numeric characters 0-9 and special characters.When information is represented internally, as Binary information, eight characters make up a IIwordll • The word is referred to in this way only since eight characters have a total of
48
bits, a word has48
bits, and a character is not split between words. Alpha information is thought of as a number of characters grouped together in successive words to form a IIstring.1I The first character of a string is in the lowest memory location. The character in a string succeeding a character which occupies the last character position of a word is the first character in the word with the next higher memory location.Information is recorded in variable length groups with blank spaces of tape between each group. These groups of information are called records. Each
record is written entirely in either Alpha or Binary mode. The length of a binary coded record may be from I to 1023 words. The alpha write operation may be terminated by a group mark detected in the W-register or when" the word
counter has been counted down to zero. A tape write instruction can only be executed in the forward direction.
The longitudinal parity character is written four and 1/2 character frames after the last character of every record. A series of records followed by an End of File character is called a file. An End of File character is a BCL II>" and is the only valid one character record. All other alpha records must be-at least
7
characters in length. All Binary records must be from 1 word to 1023 words long. An End of File character has the same bit configuration for both alpha and binary mode. Refer to Figure 5-3.FILE LONGITUDINAL
PARITY CHAR.
LABEL
~~ ~~
RECORD ~ ~
INTER
I
RECORD
Il.l.:~
END OF FILE CHARACTERGAP 4 BCL~=OOl1l1
BI NARY ~ = 00 1111
ONLY VALID 1 CHAR. RECORD
FIGURE 5-3 TAPE FILE PHYSICAL AND DIMENSIONAL CHARACTERISTICS
Magnetic tape is made with iron oxide powder mixed with a binder which holds it to a plastic base. If the oxide is held between two layers of plastiC, it is
5-3
Printed in U.S. America 1-15-69 For Form 1036993
$-4 Burroughs - B$500 Input/Output Control Training Manual
called a sandwich tape. The magnetic tape units use non-sandwich type magnetic tape. Burroughs supplies an oxide coated tape with a 1. $ mil Mylar base.
Acetate based tape (of the same size) used by some tape units can be accepted.
The Burroughs tape is wound on a plastic reel with a hub diameter of 3.7 inches which fits an expandable type reel lock.
The marker strip, on the Mylar side, is placed at approximately 11 feet from the beginning of the tape. Another marking strip, on the same side, is placed
approximately 1$ feet from the end of the tape. These marker strips are reflective pieces of aluminum foil which are used in sensing the beginning (BOT) and end (EOT) of the tape. Refer to Figure
$-4.
BASE CASTING
~ 1~ d
CAPSTAN 32 HEAD
FORWARD ]
-+-_--ll-FT 1---15-FT....---t
PHYSICAL END OF TAPE PHYSICAL BEGINNING OF TAPE
FIGURE
5-4
POSITIONING BOT AND EOT MARKER STRIPSTwo leaders are used with the TTU. A female leader, constructed of magnetic tape, is attached to the take-up reel. It is attached so that the mylar side runs next to the magnetic head. The total length of this leader is normally about 1$ feet as shown in Figure $-$. A reflective marker strip is applied to the oxide side of the leader and appears approximately 63 inches from the
junction end of the leader. This marker strip is used for the unload operation and is positioned in a manner that allows it to be s.ensed by the EOT (End-of-Tape) sensor.
A 6-inch male leader is spliced to the file tape. This leader is constructed of non-magnetic black Mylar film. It is inserted into the female leader slot by compressing the edges.
A SECOND EOT STRIP TO MARK UNLOAD POINT IS APPROVED BUT NOT REQUIRED·
---., ,...---'.
L~.QJJ L~Q!J T
(MYLAR SIDE UP
1 - - - 6 3 - I N - - - I ... - - - APPROX. 15 H . - - - i
FEMALE LEADER
FIGURE
5-5
POSITIONING UNLOAD .MAEKERSTRIPSWord
5 ...
6 Burroughs - B5500 Input/Output Control Tl'~JJiing~anualMAGNETIC TAPE WRITE (Always performed ifi the forward direction) D48,47 ifistruction used primarily by MCP.
=
1 No Data Transfer (Erase or Space Operation) XX (integer, contifiuity bits)=
0 Alphanumeric WriteWords are written from successively higher memory addresses.
MAGNETIC TAPE READ
D29,28 D27 D26 D25
D24
Burroughs - B5500 Input/Output Control Training Manual
=
xx (Integer Continuity bits)MAGNET TAPE WRITE RESULT DESCRIPTORS The basic
5-8 Burroughs - B5500 Input/Output Control Training Manual
D20 = 1 A vertical character parity error from tape to I/O on either a longitudinal parity error has been detected. In model III rio's a drop-out being detected forces the set of the parity error flag.
D2l = 1 An End-of-file character (a BCI ~ = Q9 1111) has been detected in
the IB register.
D22 Not used in a read result descriptor D23 Not used
D24 -c-D30 See Figure 5-6 .
D3l, D32, D33 Contains the contents of the character counter at End-of-operation (EOPS) time.
FORWARD: If D3l ~ 33
=
0, the last word read was a full word.If D3l ~ 33
r
0, then the number of characters read in the last word is contained in D3l ~ 33.BACKWARD: D3l => 33
=
7 the last word read was a full word. If D3l => 33r
7 then the contents of D3l ~ 33 subtracted from 7 equals the number of characters stored in the last partial word.D34, D35, D36, D37 and D46 along with D19 are utilized the same as in a write operation.
TAPE OPERATIONS CONTAINING QUESTION MARKS CHARACTER COUNTER: ________
~~~~~~~~~~~~~~~~~
W-REGISTER:---f~~~~~~~~~~~~~~~~
INFORMATION IN MEMJRY:/